ASE 8 - Engine Performance. Module 9 Ignition Systems

Transcription

1 ASE 8 - Engine Module 9

2 Acknowledgements General Motors, the IAGMASEP Association Board of Directors, and Raytheon Professional Services, GM's training partner for GM's Service Technical College wish to thank all of the people who contributed to the GM ASEP/BSEP curriculum development project This project would not have been possible without the tireless efforts of many people. We acknowledge: The IAGMASEP Association members for agreeing to tackle this large project to create the curriculum for the GM ASEP/BSEP schools. The IAGMASEP Curriculum team for leading the members to a single vision and implementation. Direct contributors within Raytheon Professional Services for their support of translating a good idea into reality. Specifically, we thank: Chris Mason and Vince Williams, for their leadership, guidance, and support. Media and Graphics department under Mary McClain and in particular, Cheryl Squicciarini, Diana Pajewski, Lesley McCowey, Jeremy Pawelek, & Nancy DeSantis. For their help on the Engine curriculum volume, Subject Matter Experts, John Beggs and Stephen Scrivner, for their wealth of knowledge. Finally, we wish to recognize the individual instructors and staffs of the GM ASEP/BSEP Colleges for their contribution for reformatting existing General Motors training material, adding critical technical content and the sharing of their expertise in the GM product. Separate committees worked on each of the eight curriculum areas. For the work on this volume, we thank the members of the Engine committee: Jamie Decato, New Hampshire Community Technical College Lorenza Dickerson, J. Sargeant Reynolds Community College Marvin Johnson, Brookhaven College Jeff Rehkopf, Florida Community College at Jacksonville David Rodriguez, College of Southern Idaho Paul Tucker, Brookdale Community College Kelly Smith, University of Alaska Ray Winiecki, Oklahoma State University - Okmulgee

3 Contents Overview... 4 Primary Circuit... 5 Triggering... 5 Secondary Circuit... 5 Coil... 5 The Principle of Mutual Induction... 6 Types of Systems... 7 Distributor Ignition... 7 DI Secondary Operation... 8 Spark Plugs... 9 Electronic Ignition (EI)...11 EI Secondary Operation Types of Systems IC Timing Triggering Devices Permanent Magnet (PM) Generator Integrated Direct Ignition (IDI) Up-Integrated Direct Ignition (UIDI) L, 4.6L Direct Ignition System (DIS) Hall Effect Switch Computer Controlled Coil Ignition (C31) C31 Crank and Cam Sensors C31 Type 1 & 2 Fast Start Crankshaft Sensor Adjustment Single Shot Sensor Adjustment Ignition Control / X Reference Low Camshaft Position (CMP) Sensor Magneto Resistive Sensors... 32

4 HVS Distributor Ignition System Overview Ignition Control Camshaft Retard Offset Adjustment (Truck V8) Coil-Near-Plug Crankshaft Position Sensor and Reluctor Wheel Camshaft Position Sensor Ignition Coils/Modules Optical Pick-Up Sensor Opti-Spark Ignition System Noteworthy Ignition Information Diagnosing Coil-On-Plug Ignition System Spark Plugs Powertrain Control Module Dual Knock Sensors Crankshaft Position (CKP) Sensor Camshaft Position (CMP) Sensor... 52

5 Overview Ignition systems have changed significantly in recent years. They have gone from mechanically driven distributors with breaker points, to an electronically controlled distributorless system (Figure 8-1). Emissions and fuel economy requirements, together with changing engine designs and packaging needs, have all contributed to these changes. As a result of the combustion characteristics of today's engines (high swirl/ turbulence), and the dilution of the mixture due to EGR gases, the energy requirements of the ignition system have increased significantly. To meet these requirements, today's ignition systems are capable of producing voltages greater than 1 00,000 volts. At the same time, these newer systems require little or no maintenance, as compared to the older mechanical systems. This section will describe the different types of ignition systems currently being used. It will cover the components and operation of the most commonly used GM systems. Figure 8-1, Typical Ignition System While discussing ignition secondary systems, we will use electron flow instead of conventional current flow. Conventional flow is from positive to negative; electron flow is from negative to positive. On conventional distributor ignition systems, the center terminal of the plug is always negative. That is, the electrons leave from the center electrode and arrive at the outer electrode. The electrons return through the block and other circuitry to the source, the secondary coil winding. Consider the secondary winding as a source in itself; the energy does not have to be common to the 12 volt source at any point to operate properly. All ignition systems are made up of three sections or sub-groups (Figure 8-2): Primary Triggering Secondary 9-5

6 Figure 8-2, Ignition System Basics Primary Circuit The primary section of the ignition system includes all of the components and wires operating on low voltage (12 volts or system voltage). The primary circuit includes the ignition switch, coil primary windings, a switching device (ignition module), and all associated wires and connectors. Triggering All ignition systems require a circuit to turn on and off the current flow in the primary winding of the ignition coil. The triggering section is considered to be any form of signal that is an input to the ignition module or PCM for switching of the coil. Examples of triggering signals are pickup coil signals, CKP sensor signals, and ignition module inputs to and from the PCM, such as reference high and Ignition Control (IC). There are four categories of triggering devices: Permanent Magnet (PM) Generator (also known as Variable Reluctance Sensor), Hall Effect Switch, Optical Pickup, and Magneto Resistive (MR). Ignition systems using each type of these devices will be covered in detail later in this section. Secondary Circuit The secondary circuit of the ignition system is the high voltage section (up to 1 00,000 volts) - It consists of the: ignition coil(s), plug wires, and spark plugs. In the case of a DI system, there is also a distributor cap and rotor. Coil The coil is a major component of the secondary circuit. It provides the voltage required to overcome the resistance of the secondary circuit. The coil is designed to take a small amount of voltage, volts, and step it up to a much higher voltage. In these ignition systems, secondary voltage requirements can be anywhere from 6,000 volts (6kV) up to 1 00,000 volts (1 OOKV). The coil is a type of step-up transformer and can greatly increase secondary voltage (Figure 8-3). The coil is part of both the primary and secondary circuits. When the primary coil switches open, the magnetic field collapses and secondary voltage is induced in the secondary coil windings. 9-6

7 The Principle of Mutual Induction A current flow through a primary coil winding produces a magnetic field through a second coil winding, wound around a common steel core. When the primary coil current is shut off, the magnetic field collapses and current is "induced" in the secondary windings. Figure 8-3, Basic Induction Principles Coil output is affected by three factors. The first is the amount of current that can flow through the primary winding. The more current that can flow then the stronger the magnetic field will be. The second is the number of turns of wire on the secondary side. The more turns, the higher the voltage output. The third is the diameter of the wire used. These factors together dictate the coils output (Figure 8-4). Several factors limit ignition coil output. When a coil steps up voltage, the amperage is proportionally decreased. If the current flow through the coil primary winding is low, the current on the secondary side may be significantly lower. If secondary resistance becomes excessive, there may not be enough energy to jump the spark plug gap. This could cause a misfire, or possibly damage the coil or ignition module. Figure 8-4, Cross-Section of Remote Mounted Ignition Coil 9-7

8 Types of Systems Although there are many variations of ignition systems currently being used, they all fall into two major categories: Distributor Ignition (DI) systems and Electronic Ignition (El) systems. Distributor Ignition Distributor Ignition (DI) systems with electronic controls have been used on GM engines since the midseventies, Since that time, they have been constantly refined and improved. Ignition systems have evolved and today are highly sophisticated electronic systems with fewer moving parts and minimal adjustments. Timing is computercontrolled and better meets the changing conditions of the engine. The most common form of DI is the Figure 8-5, Distributor Assembly High Energy Ignition system (HEI). Some advantages of the HEI system are: The ability to fire EGR diluted mixtures under high swirl/turbulence conditions Extended spark plug life Fewer moving parts with reduced service The signal for ignition timing can be precisely controlled by the PCM Coil primary current is controlled electronically by solid-state circuitry Components The typical HEI system contains: Distributor Assembly (Figure 8-5) Pickup Coil Ignition Module Ignition Coil Cap and Rotor 9-8

9 DI Secondary Operation Distributor Cap and Rotor On DI ignition systems, a cap and rotor distribute (or route) the secondary voltage to the correct spark plug at each cylinder (Figure 8-6). Since air gaps are present between the rotor and cap contacts, arcing occurs. On HEI distributors, the arcing has the tendency to erode and deteriorate the contacts and, therefore, Figure 8-6, Distributor Cap and Rotor inspecting the cap should be part of normal system maintenance. On HVS distributors, significant improvements have eliminated the need for routine inspection. Spark Plug Wires Spark plug wires carry the high secondary voltage from the coil, or distributor cal), to the spark plugs. They are made of silicone rubber with a fiber core that acts as a resistor to reduce secondary current. This cuts down on radio and television interference (TVRS), and Figure 8-7, Spark Plug Wire Resistance reduces spark plug wear. The insulated boots at the end of the wires strengthen the connections to the plug and keep out dust and moisture, as well as prevent voltage loss. Typically, the resistance of a spark plug wire should be less than 30,000 ohms (Figure 8-7). Refer to the Service Manual for specifications on each model. High resistance can cause a misfire and possible coil damage. The wire can be damaged if it is not carefully removed from the plug. Twist the boot to loosen, or use removal tool J to remove wires. If the boot is equipped with aluminum heat shields, make sure that the shield is properly seated when the boot is installed. IMPORTANT Never puncture a spark plug wire or its boot to test the ignition system. Damage caused by puncturing spark plug wires may lead to a misfire condition, coil failure or ignition module failure. 9-9

10 Spark Plugs The spark plug provides an air gap through which the secondary voltage arcs and ignites the air/fuel mixture in the engine (Figure 8-8). The basic plug consists of a ceramic insulator, and a pair of electrodes. Most plugs have a resistor which, like the wires, reduces current in the secondary system. Spark plugs must be the correct size, reach, and heat range for a specific Figure 8-8, Spark Plug application. It is important to use the spark plug specified for a particular engine. Spark plug electrodes are subjected to extreme heat, pressure, and corrosion. As a result, they should be included in normal maintenance. Arcing tends to deteriorate the electrodes over time, so a higher spark voltage is required to jump the gap. Fouling may provide an alternate path for the spark, which causes misfires. Wetting of the plug may also short out the electrodes. Cracked insulators, carbon tracking, burned electrodes, and improper torque can all lead to undesirable performance and premature failure. Extended Life Spark Plugs The extended life spark plug has a nickel plated shell to improve resistance to corrosion for the life of the vehicle. It uses a copper core center electrode to improve resistance to low speed carbon fouling. Platinum tips are used on the center electrode and side electrode to prevent spark erosion (which contributes to gap growth). The tip also minimizes ignition demand voltage due to a smaller surface area. Figure 8-9, Extended Life Spark Plug (Advanced Composition Igniter Series) 9-10

11 Hi-Efficiency Life Spark Plug The Hi-Efficiency spark plug has a fine wire center electrode. The center electrode contributes to a more efficient transfer of electrical energy to thermal energy by allowing more flame kernel growth before contact with the other relatively cold spark plug features. In this way, more of the spark energy is converted to burn energy. Other features include: Fine wire platinum electrodes that are extremely resistive to wear A nickel plated shell for resistance to corrosion A ribless insulator design that provides a better seal with the secondary boot A larger gap than conventional plugs, which enhances burn characteristics Figure 8-10, Hi-Efficiency Spark Plug (Platinum Tip Spark Plug Series) AC Spark Plug Numbering System IMPORTANT In order to prevent any confusion or misapplication of the spark plugs, a numeric identification code was developed. The numeric code does not in any way correspond to the heat range of the spark plug. Therefore, selection of a spark plug with a different code number is not recommended. The heat ranges may be drastically different between the two different plugs and engine damage or poor performance may result. Figure 8-11, AC Spark Plug All Numeric Identification Code 9-11

12 Electronic Ignition (EI) The Electronic Ignition (EI) system was designed to replace the mechanical Distributor Ignition (DI) system. EI eliminates many of the mechanical parts of a DI system that could possibly fail. Components The components that make up a typical El system are listed below (Figure 8-12): Ignition Module Ignition Coils Crankshaft Sensor Camshaft Sensor (in some applications) Interrupter or Reluctor Advantages Fewer moving parts Figure 8-12, EI Components More compact mounting Remote mounting capability Elimination of mechanical timing adjustments Less maintenance No mechanical load on engine Increased available coil saturation time (dwell time) More coil cool down time between firing events The terms that are used when referring to the Electronic Ignition (EI) System are determined by the actual vehicle application of the system. The EI systems currently used are: Computer Controlled Coil Ignition (C31) Direct Ignition System (DIS) Integrated Direct Ignition (IDI) Up-integrated Direct Ignition (UIDI) Coil Per Plug (CPP) 9-12

13 EI Secondary Operation In an EI System, a spark plug is attached to each end of the ignition coil secondary. Each coil of the system fires the plugs in two companion cylinders (Figure 8-13). These are cylinders that reach Top Dead Center (TDC) at the same time. The cylinder that is at TDC on the compression stroke is referred to as the "event" cylinder while the cylinder at TDC on the exhaust stroke is the "waste" cylinder. When the coil discharges, both plugs fire at Figure 8-13, Companion Cylinders the same time to complete the series circuit. Since the polarities of the ignition primary and secondary windings are fixed, one plug always fires in a forward direction, while the other always fires in reverse (Figure 8-14). This arrangement requires somewhat more energy than conventional systems. Coil design, saturation time and primary current flow on El systems are able to produce the necessary energy to accomplish this. Since both plugs in companion cylinders fire at the same time, it Figure 8-14, EI Current Flow is not necessary for the module to recognize which cylinder is on which stroke. Because of lower pressure in the cylinder on the exhaust stroke, its plug requires less voltage to produce an arc. Therefore, most of the available voltage is used to fire the plug in the cylinder that is on the compression stroke. CAUTION No ignition coil is designed to be run with the secondary unloaded. However, this is particularly true with distributorless ignition systems. The high voltage produced by these systems can cause personal injury and/or system component damage. 9-13

14 IMPORTANT A spark tester that requires 25,000 volts is required to adequately load the secondary portion of the ignition system (ST-1 25, J-26792). Other spark testers may not require 25,000 volts and therefore could lead to misdiagnosis. Types of Systems So far, we have covered two types of ignition systems; Distributor Ignition (DI) systems and Electronic Ignition (EI) systems. These can be further broken down into two sub-categories: Up-Integrated Systems Bypass Systems Up-Integrated Systems In an up-integrated ignition system (figure 8-16), all ignition coil timing is controlled by the PCM. The triggering signal, from either the crankshaft position (CKP) sensor or the pickup coil, is a direct input to the PCM. The PCM processes the triggering signal, along with other inputs, and provides the ignition control module with an ON/OFF signal. Based on the ON/OFF signals from the PCM, the ignition control module turns the coils on and off, providing secondary voltage for the spark plugs to fire. The main function of the ignition control module in an up-integrated system is to: Turn the coils on and off based on IC signals from the PCM Limit primary current flow (in some applications) In some cases, the ignition control module still receives the CKP signal. The ignition control module, in these cases, is just a processor for the CKP signal. It passes the signal to the PCM, sometimes converting it from an AC signal to a DC signal, but has no control of ignition timing. Figure 8-16, Up-Integrated System 9-14

15 Bypass Systems In a bypass system, the ignition control module processes the triggering device signal. Because the triggering device signal can be either an AC signal from a PM Generator, or a DC signal from a Hall Effect Switch or Optical pickup, the module sometimes must convert the signal from an AC signal to a DC signal. The ignition control module provides an ignition control (IC) reference signal to the PCM based on the signal from the triggering device Primary coil current is controlled by either one (DI), two (EI, 4-cylinder), three (EI, 6-cylinder), or four (EI 8-cylinder) circuits in the ignition module. These circuits complete the ground path for the ignition coil primary current. The timing and the sequencing of the coil drivers are determined by several circuits within the module and the external triggering devices. IMPORTANT Because of the high current requirements of the primary ignition circuit, the ICM must have a good ground. Check all module ground connections, including the distributor housing to engine block on DI systems. Another function of the ICM is to control the bypass mode of the ignition system. In a bypass type of system there are two modes of operation: bypass and ignition control (IC, formerly called EST). Bypass can be thought of as ignition control module (ICM) controlled timing and is normally used when the engine is cranking and running below a certain rpm, or during a default mode due to a system failure. In ignition control (IC) mode, the PCM controls the timing instead of the ignition control module. During the bypass mode of operation, base timing may not be fixed. Depending on the application, some timing advance may be engineered into the ignition control module during this mode. The pickup coil or Crankshaft Position sensor (CKP) provides the signal necessary for the ignition coil to fire. When the engine is cranking below the "run threshold" (usually between 400 rpm and 600 rpm, depending on the engine), ignition timing is controlled by the ICM (Figure 8-17). Figure 8-17, Bypass Mode Timing 9-15

16 IC Timing When the engine reaches the run threshold, the PCM applies a 5-volt signal to the ICM bypass circuit. The 5-volt signal switches off the bypass circuit and switches on the IC circuit for primary ignition coil triggering. In other words, instead of using the signal that was developed by the pickup coil or CKP to fire the coils directly, the PCM adjusts this signal in relation to engine needs and uses this alternate IC signal to control the spark. Now spark timing is controlled by the PCM based on information being received from the MAP or MAF sensor, BARO, ECT, TPS and the Reference Signal (Figure 8-18). Figure 8-18, IC Timing Triggering Devices As we discussed earlier in this section, there are four categories of triggering devices: Permanent Magnet (PM) Generator (also known as Variable Reluctance Sensor), Hall Effect Switch, Optical Pickup, and Magneto Resistive (M.R.). The rest of this section will cover, in detail, examples of different ignition systems, grouped by the type of triggering device that is used. Figure 8-19, Permanent Magnet (PM) Generator (Variable Reluctance Sensor) 9-16

17 Permanent Magnet (PM) Generator The PM generator uses the principle of induction to develop an AC signal. In the example of the crank sensor, Figure 8-19, wire is coiled around a permanent magnet. By rotating a reluctor, which has notches cut into it at precise locations, the magnetic field moves back and forth across the wire winding. This produces an AC voltage signal in the wire. The ends of the wires are connected to either the ICM or the PCM. The signal is converted to an ON/ OFF reference and used as the base triggering for the primary circuit. For the crankshaft position sensor to work, it must have a.050" (±.020") air gap between the sensor and the reluctor. On El systems the sensor is mounted in the block or the Figure 8-20, Pickup Coil Operation front cover and is non-adjustable. On a DI system, the pickup coil operates similarly. A magnetic field increases and decreases as the teeth of the timer core and the pole piece move in and out of alignment (Figure 8-20). This induces an alternating current flow through the pickup coil, which is the triggering signal to the ICM. Law of Induction "Electricity creates magnetism, and magnetism creates electricity..." In other words, current flowing through a conductor creates a small magnetic field around the conductor. And conversely, any time a magnetic field is allowed to cut through a conductor, current flow is produced in the conductor. It is this principle that is used in PM Generators. 9-17

18 PM Generator output voltage varies with engine speed. Typical values range from approximately 500 millivolts at cranking speeds to 100 volts at high rpm, depending on the application. When measuring the output from a magnetic crank sensor, the voltmeter should be set on an appropriate AC scale. The output from a PM Generator in a given engine will vary based upon the following: Cranking speed Air gap of sensor to reluctor Resistance of sensor windings Temperature of sensor Strength of magnet EI systems use a PM Generator and a reluctor that is part of the crankshaft. The design of the Figure 8-21, Reluctor/Sensor Triggering (4 and 6 Cylinder Engines) crankshaft reluctor is an important consideration when diagnosing these systems. Crankshaft reluctors on most four- and six-cylinder engines have seven notches that each send voltage signals to the ignition module for every revolution of the crankshaft. Six of the notches are equally spaced at 60-degree intervals around the crankshaft. The seventh notch is positioned 10 degrees from the sixth notch. The signal from the seventh, or "SYNC," notch synchronizes the coil firing sequence with crankshaft position (Figure 8-21). On four-cylinder engines, the ignition module is programmed to recognize the sync notch, count notch number 1 and accept notch 2 as the signal to fire the 2-3 companion cylinders. Next, the module counts notches 3 and 4, then accepts the number 5 notch signal as the signal to fire the 1-4 cylinder pair. The 6 and 7 notches are then counted and the process begins again. Note that the coil pack for the second cylinder in the firing order always fires first during start-up. 9-18

19 On 60-degree V6 engines, the module skips the number I notch after the sync signal, and fires the 2-5 cylinders on the signal from notch 2. Notch 3 is skipped and notch 4 fires the 3-6 cylinder pair. Finally, notch 6 is used to fire the 1-4 pair. See Figure 8-22 for a scope pattern display of the sensor output. Figure 8-22, Crankshaft Reference Pulses Integrated Direct Ignition (IDI) Integrated Direct Ignition (IDI) is used exclusively on the 2.3/2.4L SOHC/ DOHC family of engines. This system is similar to the DIS system in operation, with some additional advantages. Like DIS, this system uses a magnetic crank sensor and a reluctor on the crankshaft. Most other components of the system, including the module, coils, and spark plugs, are contained in one assembly (figure 8-23). There is lower secondary circuit resistance since this system uses a boot instead of a carbon resistor wire to the spark plug. The IDI system has gone through several changes since it was first introduced. Although the module may look identical, it may not be interchangeable from one model year to another because of internal operation. Also, the coils have been upgraded several times. Check service bulletins to make sure you get the correct part number. Figure 8-23, IDI Components 9-19

20 Figure 8-24, 2.4L Ignition System 9-20

21 Up-Integrated Direct Ignition (UIDI) Another variation to the IDI system is the Up-integrated Direct Ignition (UIDI). This system no longer has bypass timing control in the ignition module. Instead, all timing control is up-integrated to the PCM (Figure 8-25). Because of this, there are fewer pins on the module than on past models. Figure 8-25, UDI Circuit 9-21

22 4.0L, 4.6L Direct Ignition System (DIS) The 4.0/4.6L V8 DIS has dual variable reluctance crankshaft sensors with one reluctor ring to monitor crankshaft position (Figure 8-26). The reluctor ring has 24 evenly spaced notches and 8 unevenly spaced notches. With one sensor mounted 271, of crankshaft revolution behind the other, a unique pattern of pulses is created that allows the ignition to synchronize and fire the first coil in less than 1/2 (18011) crankshaft revolution. The ignition module accomplishes this by monitoring the pulses it receives from each crankshaft position sensor. The ignition module counts the number of "B" pulses between "A" pulses. The pattern on the reluctor ring allows 0, 1, or 2 B's between A's. When the module recognizes one of four patterns of B's between A's (0112, 01012, 0ll11, ), the crankshaft position is known and the ignition system is synchronized. The ignition can synchronize at four different crankshaft positions. Therefore, the first cylinder fired at engine start-up will depend on where, or what position, the engine stopped at the previous key-off. The system also uses a magnetic camshaft position sensor for fuel control and misfire diagnostics. Figure 8-26, 4.0L/4.6L Crankshaft Position Sensors 9-22

23 Hall Effect Switch The Hall Effect Switch is an electronic device that produces a voltage signal controlled by the presence or absence of a magnetic field in an electronic circuit. The Hall Effect Switch is used on several EI applications. A regulated signal voltage from the ignition module is passed through a semiconductor wafer in the Hall switch. A permanent magnet mounted beside the semiconductor induces Hall voltage across the semiconductor (Figure 8-27). The crank sensor is positioned so that metal blades or "vanes" of an interrupter ring, mounted on the crankshaft harmonic balancer/damper pass between the semiconductor and the permanent magnet. When a metal vane comes between the magnet and the semiconductor, the magnetic field is interrupted and Hall voltage drops off (Figure 8-28) Hall voltage is amplified and routed to the base of a transistor which controls the ground on the signal voltage from the ignition module. When full Hall voltage is present (no vane inside sensor), the transistor is ON and the signal from the module is grounded (pulled low to volts). When Hall voltage drops (vane inside sensor), the transistor turns OFF and the signal returns to the high state. As the interrupter rotates, signal voltage alternates between high and low states, generating a square-wave with the same "pattern" as on the interrupter vanes. Note that it is the module supply voltage that is pulled low by the sensor. Figure 8-27, Hall Effect Switch ON Figure 8-28, Hall Effect Switch OFF 9-23

24 "The Hall Effect" When a magnetic field is introduced perpendicular to a current flowing through a semiconductor, a measurable voltage is induced at the sides of the semiconductor, at right angles to the main current flow (figure 8-29). Figure 8-29, Hall Effect Pull-UP/Pull-Down Hall Switching Hall Effect switches can be either "pull-up" or "pull-down." In other words, the hall effect switch may be switching an internally sourced voltage (from module) to ground, or switching an externally sourced supply voltage to the module. Always refer to the appropriate service manual electrical schematics when performing diagnosis on ignition systems. It is important to know if the circuit you are diagnosing is pull-up circuit or a pull-down circuit, especially in an ignition system. Remember: A "pull-up" circuit (Figure 8-30) has a power source outside the PCM. The PCM does not provide the reference voltage signal. When the switch is closed, external source voltage provides a high reference signal to the PCM. An open switch, 6n the other hand provides a low reference signal. A "pull-down" circuit (Figure 8-31) is provided with a reference voltage signal from the PCM. The power source for the circuit is internal to the PCM. When the switch is closed, source voltage is pulled low to an external ground. The PCM registers a low voltage reference signal. When the switch is open, the PCM registers a high reference signal. Figure 8-30, Pull-Up Circuit Figure 8-31, Pull-Down Circuit 9-24

25 Computer Controlled Coil Ignition (C31) The EI system known as C31 is used on the 3.OU3300 and the 3.8U3800 V6 engines. This system has Hall Effect switches for crank and cam position with the interrupter ring mounted on the back side of the harmonic balancer, an ignition module, and a coil pack assembly (Figure 8-32). There are two coil pack designs, Type I and Type 11, which are interchangeable on some models (Figure 8-33). A variation to this system, known as the Fast Start, uses a unique interrupter ring which gives more precise crank information. This system provides faster starts by supplying information for correct cylinder firing without relying on the cam signal. Figure 8-32, C31 Components Figure 8-33, Type I and Type II Coil Packs Figure 8-34, Ignition System Resistance Tests 9-25

26 C31 Crank and Cam Sensors 3.0-liter, 3.8-liter, 3300 and 3800 V6 engines use Hall Effect switches for both the crankshaft signal and the camshaft signal. The crankshaft position (CKP) sensor on the 3.0-liter engine is located adjacent to the crankshaft harmonic damper. Two concentric rings on the back of the damper pass on each side of the Hall Effect magnet. The inner ring has three evenly spaced vanes and windows, which send identically timed signals of the same duration. The outer ring has only one window. This single pulse acts as the synchronize signal to set up the logic for triggering the correct ignition coil (figure 8-36). On the 3.8-liter SFI and SFI Turbo engines, the synchronize signal is determined by a separate camshaft sensor. The magnet is mounted in the camshaft sprocket (figure 8-37). The cam sensor signal identifies cylinder sequence for injector firing on Sequential Fuel Injection systems, as well as the "sync" signal for the ignition module. Figure 8-35, Crankshaft Sensor, 3.8L V-6 LG2 Engine Figure 8-36, 3.0L v-6 Crankshaft Position Signal Figure 8-37, 3.8L SFI Crankshaft Position Signal 9-26

27 C31 Type 1 & 2 Fast Start 3800 Engine The C31 Fast Start system on the 3800 and engines use a dual crankshaft sensor and a separate cam sensor. Advantages of the Fast Start system are: Faster start-up Walk-home protection in the event of cam sensor malfunction More precise measurement of crankshaft sensor signals On the Fast Start (pre 1993) systems, the dual crank sensor is mounted on the front of the engine beside the harmonic balancer/crankshaft pulley. The cam sensor is mounted on the timing cover beside the cam sprocket. The arrangement of the interrupter rings on the harmonic balancer is different than on the other V6 engines. First, the outside ring has 18 evenly sized and evenly spaced interrupter blades to produce 18 pulses per crankshaft revolution. These pulses are known as the 18x signal. The inside ring has three interrupter blades with gaps (or windows) of 10, 20 and 30 degrees. These gaps, in turn, are spaced 100, 90 and 110 degrees apart respectively. These pulses are referred to as the 3x signal (Figure 8-38). With this interrupter ring arrangement, the ignition module can identify the proper cylinder pair to fire within as little as 120 degrees of crankshaft rotation. The module can also fire any cylinder pair reaching TDC first without waiting for the cam or sync. signal. The 1-4 cylinder pair reaches TDC 75 degrees after the trailing edge of the 10 degree window. TDC of the 6-3 pair is 75 degrees after the trailing edge of the 20 degree window. TDC of the 2-5 cylinders occurs 75 degrees after the trailing edge of the 30 degree window. The trailing edges of the windows are each 120 degrees apart. Figure 8-38, 3800 V6 Crankshaft and Camshaft Signals 9-27

28 Figure 8-39, 3.8L Ignition System 9-28

29 Crankshaft Sensor Adjustment 3.0L, 3.8L, 3300, 3800 V6s Use the crankshaft sensor adjusting tool (J-37089) to ensure accurate positioning of the sensor, and to maintain proper clearance between the interrupter vanes and the sensor. The tool is also used to check interrupter rings for out-of-round. The procedure for using adjusting tool J (Figure 8-36) is as follows: 1. Loosely install crankshaft sensor on pedestal. 2. Position sensor, with pedestal attached, on adjusting tool J Position adjusting tool on crankshaft. 4. Install bolts to hold pedestal to block face, torque to Nm (30-35 lb. ft.). 5. Torque pedestal pinch bolt to 3-4 Nm (30-35 lb. in.). 6. Remove adjusting tool J Place adjusting tool J on harmonic balancer and turn (Figure 8-40). The tool should turn freely without contacting any of the interrupter ring vanes. If any vane touches the tool, replace the harmonic balancer. Adjusting tool J can be used to adjust all crankshaft sensors, with the exception of the Delco single-slot design sensor and late model 3800s. Figure 8-40, Crank Sensor Adjustment Using J

30 Single Shot Sensor Adjustment Single slot design crankshaft sensors (Figure 8-41) are adjusted using the Kent-Moore feeler gage style adjusting tool, J36179 as follows (Figure 8-42). 1. Rotate the harmonic balancer with a 28mm socket and a pull handle, until the interrupter ring fills the sensor slot and the edge of interrupter window is aligned with the edge of the deflector on the pedestal. 2. Insert adjustment tool (J or equivalent) into gap between sensor and interrupter on each side of interrupter ring. If gage does not slide past the sensor on either side of interrupter ring, the sensor is out of adjustment or the interrupter ring is bent. This clearance should be checked at three positions around the outer interrupter ring, approximately 120 degrees apart. 3. Loosen the pinch bolt on sensor pedestal. Insert adjustment tool (J or equivalent) into the gap between the sensor and interrupter on each side of the interrupter ring (Figure 8-42). 4. Slide the sensor into contact against gage and interrupter ring. 5. Torque the sensor retaining pinch bolt to 3.4 Nm (30 in. lbs.) while maintaining light pressure on the sensor against the gage and interrupter ring. Check again at three locations approximately 120 degrees apart. If the interrupter ring contacts the sensor at any point during harmonic balancer rotation, the interrupter ring has excessive runout and must be replaced. Figure 8-41, Single Shot Design Crankshaft Sensor Figure 8-42, Crank Sensor Adjustment Using J

31 Ignition Control /3400 The 3100/3400 ignition system is a hybrid ignition system that uses two crankshaft position sensors. The 24X (Hall Switch) CKP signal is directly input to the PCM, while a 7X (Permanent Magnet Style) CKP signal is input to the ignition control module. The ignition control module sends a 3X signal to the PCM. The 3X signal is a conditioned signal (by the ignition control module) based on the 7X CKP signal. Below 1250 RPM, the PCM controls ignition timing and idle speed using the CKP 24X signal. Minor changes in idle speed are corrected by the PCM with spark control, known as "dynamic spark" Major changes are handled by the IAC motor (Figure 8-43). Figure 8-43, Closed Loop Idle Control Figure 8-44, 24X Crankshaft Position Sensor 9-31

32 X Reference Low The PCM uses the 3X signal from the ignition control module to calculate engine speed and crankshaft position over 1250 RPM. If the PCM receives no pulses on this circuit, DTC P 1374 sets and the PCM uses the 24X reference signal circuit for fuel and ignition control. Camshaft Position (CMP) Sensor The CMP sensor (Figure 8-45) sends a cam position signal to the PCM, which uses it as a sync pulse to trigger the injectors in proper sequence. The PCM uses the CMP signal to indicate the position of the #1 piston during its intake stroke. This allows the PCM to calculate true Sequential Fuel Injection (SFI) mode of operation. If the PCM detects an incorrect CMP signal while the engine is running, DTC P0341 sets. If the CMP signal is lost while the engine is running, the fuel injection system shifts to a calculated sequential fuel injection mode based on the last fuel injection pulse, and the engine continues to run. The engine can be restarted and runs in the calculated sequential mode as long as the fault is present, with a one in six chance of injector sequence being correct. Refer to DTC P0341 for further information. Figure 8-45, Camshaft Position Sensor 9-32

33 Figure 8-46, 3100 Ignition System 9-33

34 Magneto Resistive Sensors The CKP sensor (Figure 8-47) on late model General Motors trucks is a magneto-resistive (MR) sensor that generates a digital signal. The MR sensor is similar in operation to a Hall Effect switch. Both sensors require a magnetic field to operate, have three wires, and output a digital signal. A permanent magnet is located inside the sensor end nearest the crankshaft reluctor wheel (Figure 8-48). The magnet is positioned between two magnetic reluctance pickups, MR1 and MR2. The magnetic field changes in the area of MR1 and MR2 as the reluctor wheel passes. Each tooth of the reluctor wheel reaches MR1 first, then MR2. Both MR1 and MR2 produce identical voltage signals, but the MR2 signal is just a fraction of a second later than the MR1 signal because of its location to the approaching reluctor wheel. Both the crankshaft position sensor and the reluctor wheel should be handled carefully. Any dents or other imperfections in the wheel can cause excessive crankshaft position sensor noise. A damaged reluctor wheel or crankshaft position sensor may cause improper operation of on-board diagnostics, such as the misfire diagnostic. Figure 8-47, Crankshaft Position Sensor, 1995 S/T Utility/Pickup (L35 Engine with HVS Ignition) 9-34

35 Figure 8-48, Crankshaft Reluctor Wheel, 1995 S/ T Utility/Pickup (L35 Engine with HVS Ignition) Signals from MR1 and MR2 cause a differential amplifier to produce the MR differential output (Figure 8-49). This signal is used to switch a Schmidt Trigger on and off. The sensor output is then like that of a Hall Effect switch. One difference from most Hall Effect switches is that the VCM does not supply a pulled up signal wire for the sensor to toggle to ground. Instead, the MR sensor pulls up the signal wire to 5 volts and toggles it to ground. A Figure 8-49, Magneto Resistive Crankshaft Position Sensor Operation 9-35

36 Figure 8-50, 6 Cylinder Cam and Crank Signals HVS Distributor Ignition System Overview The ignition system used on late model truck applications, called the HVS Distributor Ignition System, features a high energy ignition coil and ignition coil driver module (Figure 8-51). Each engine application of this enhanced ignition system has a unique distributor. 4.3L V6 non-adjustable 6.0 and 5.7L V8 adjustable* 7.4L V8 adjustable* *Adjustable to eliminate the chance of crossfire only, not for timing adjustment. Trigger information for ignition timing is supplied by a Crankshaft Position (CKP) sensor. The CKP sensor is located in the timing chain cover. The CMP sensor is located in the distributor base, and is used to sequence the fuel injectors and for on-board misfire diagnostics. Figure 8-51, High Energy Ignition Coil and Driver Module Figure 8-52, Truck Distributor 9-36

37 Ignition Control The High Voltage Switch distributor appears similar to a typical distributor, but key operational features make it very different (Figure 8-52). The HVS distributor does not provide engine position information for spark delivery. Therefore, rotating the HVS distributor does not change ignition base timing. The VCM contains the base timing information within its calibration. Figure 8-53, 6 and 8 Cylinder Radial Secondary Towers The ignition coil driver module is mounted with the high energy coil (Figure 8-54). The Vehicle Control Module (VCM) controls the coil driver module. The coil driver module, in turn, controls current through the primary winding of the coil. Note that the coil driver module has no backup (bypass) mode. Base timing is not adjustable because the crank sensor, not the distributor, determines base timing. This makes it the main sensor for fuel and spark. As a result, the engine will not run without a crankshaft position sensor signal, because the ignition coil driver module doesn't have system trigger information. The crank sensor is located on the front of the engine in the timing cover. The HVS Distributor Ignition system uses crankshaft and camshaft position signals as inputs to the VCM. The VCM then uses the Ignition Control (IC) circuit to signal the coil driver module to control spark timing (Figure 8-55): The Crankshaft Position (CKP) sensor signal is used to determine engine position and speed. The Camshaft Position (CMP) sensor signal (.5X signal) identifies piston position. The CMP sensor is used to sequence the fuel injectors and detect misfire for OBD 11 diagnostics. The VCM uses the IC signal to control advance and retard based upon engine load, atmospheric pressure, rpm, and engine temperature. Since the distributor has no influence on base timing, turning it will not modify base timing in any way. However, the distributor on V8 applications is adjusted to eliminate the chance of crossfire at an adjacent terminal. Distributor terminal crossfire can be evident by poor performance, as the control module will reduce the operating window for spark advance and retard. 9-37

38 Figure 8-54, HVS Distributor System 9-38

39 Figure 8-55, 4.3L Ignition System 9-39

40 Camshaft Retard Offset Adjustment (Truck V8) Test Procedure The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To ensure proper alignment of the distributor, perform the following: 1. With the ignition OFF, install a scan tool to the DLC. 2. Start the engine and bring to normal operating temperature. IMPORTANT Cam Retard Offset reading will not be accurate below 1000 RPM 3. Increase engine speed to RPM 4. Monitor the Cam Retard Offset. 5. If the Cam Retard indicates a value of 0 ± 2, the distributor is properly adjusted. 6. If the Cam Retard does not indicate 0 ± 2, adjust the distributor. Adjusting Procedure 1. With the engine OFF, slightly loosen the distributor hold-down bolt. IMPORTANT Cam Retard Offset reading will not be accurate below 1000 RPM 2. Start the engine and raise engine speed to RPM. 3. Using a scan tool monitor Cam Retard Offset. 4. Rotate the distributor as follows: 5. To compensate for a negative reading, turn the distributor counterclockwise. 6. To compensate for a positive reading, turn the distributor clockwise. 7. Repeat step 4 until 0 ± 2 is obtained. 8. Turn off the ignition. 9. Tighten the distributor holddown bolt to 3 Nm (25 lb. ft.) 10.Start the engine, raise engine speed to 1000 RPM and check Camshaft Retard Offset again. Figure 8-56, Truck V8 Crossfire Limits 9-40

41 Coil-Near-Plug Another ignition system that uses a magneto resistive crankshaft position sensor is the coil-near-plug system used on the LS1 engines starting in The coil-near-plug system consists of the following components/ circuits: Eight Ignition Coils/Modules Eight Ignition Control (IC) Circuits Camshaft Position (CMP) Sensor.5X Camshaft Reluctor Wheel Crankshaft Position (CKP) Sensor 24X Crankshaft Reluctor Wheel Related Connecting Wires Powertrain Control Module (POM) Crankshaft Position Sensor and Reluctor Wheel The dual magneto resistive Crankshaft Position (CKP) sensor is located in the right rear of the engine, behind the starter. The CKP sensor works with a 24X reluctor wheel (Figure 8-57). The reluctor wheel is mounted on the rear of the crankshaft. The 24X reluctor wheel has two different width notches that are 15 degrees apart. This Pulse Width Encoded pattern allows cylinder position identification within 90 degrees of crankshaft rotation. In some cases, cylinder identification can be located in 45 degrees of crankshaft rotation. The reluctor wheel also has dual track notches that are 180 degrees out of phase. The dual track design allows for quicker starts and accuracy. The CKP signal must be available for the engine to start. The CMP signal is not needed to start and operate the engine. The PCM cannot determine when a particular cylinder is on either compression or exhaust stroke by the 24X signal. The CMP sensor is used to determine what stroke the engine is on. If the Cam Sensor fails, the system will attempt synchronization by firing one of two companion cylinders, and look for an increase in the RPM. An increase in the RPM signal indicates that the correct cylinder was fired, and the engine has started. If the PCM does not detect an increase RPM signal, a re-sync will occur to the opposite cylinder. A slightly longer ranking time may be a symptom of this condition. Figure 8-57, Crankshaft Position Sensor and Reluctor Wheel ( LS1) 9-41

42 Camshaft Position Sensor The Camshaft Position (CMP) sensor is mounted through the top of the engine block at the rear of the intake valley cover (Figure 8-58). The CMP sensor works in conjunction with a.5x reluctor wheel. The reluctor wheel is located at the rear of the camshaft. The CMP sensor is used to determine whether a cylinder is on the compression or the exhaust stroke. As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The CMP sensor internal circuitry detects this and produces a square-wave signal which is used by the PCM. The PCM uses this signal in combination with the CKP 24X signal to determine crankshaft position and stroke. Figure 8-58, Camshaft Position Sensor ( LS1) Figure 8-59, Ignition Coils/Modules Ignition Coils/Modules The coil-per-plug system has eight ignition coils/modules individually mounted above each cylinder on the rocker covers (Figure 8-59). The secondary ignition wires are short compared with a distributor ignition system wire. The coils/modules are fired sequentially. There is an Ignition Control (IC) circuit for each ignition coil/module. The eight ignition control circuits are connected to the PCM. All timing decisions are made by the PCM, which triggers each coil/module individually. The ignition coil/ modules have the following circuits attached to them: Ignition Feed Circuit Ignition Control Circuit Ground Circuit Reference Low Circuit The ignition feed circuits are fused separately for each bank of the engine. The two fuses also supply the injectors for that bank of the engine. Each coil/module is serviced separately. This system puts out very high ignition energy for plug firing. Because the ignition wires are shorter, less energy is lost to ignition wire resistance. Furthermore, no energy is lost to the resistance of a waste spark system. 9-42

43 Module 9 Figure 8-60, LS1 Ignition Control ( 1 of 3) 9-43

44 Figure 8-61, LS1 Ignition Control (2 of 3) 9-44

45 Figure 8-62, LS1 Ignition Control (3 of 3) 9-45

46 Optical Pick-Up Sensor The optical pick-up was first used in 1992 on the second generation small block V-8 engines, specifically the LTI 5.7L found in Corvettes, and later in other applications. The pick-up is part of the distributor assembly that is located on the front of the engine, and is driven directly by the camshaft. The optical pick-up system provides actual crankshaft position, in degrees, to the PCM. This is possible by using a flat disk with two rows of notches cut around its circumference. One row has 360 notches, each 111 wide, while the other row has eight notches. These eight notches are arranged with the following widths: 2, 7, 2, 12, 17, 2, 22 (Figure 8-63). Figure 8-63, Optical Pick-Up Sensor Circuits and Signals The optical sensor (Figure 8-64) uses an infrared light source and receiver. When the camshaft turns, the optical pick-up produces two digital signals. The 360 notches produce a high resolution signal, while the eight notches produce a low resolution signal. Both signals are sent directly to the PCM, therefore, this is an up-integrated system with no bypass mode. The low resolution signal is used for rpm reference. Without the low resolution signal, there is no spark or fuel delivery. The high resolution signal is used to fine tune the engine's timing, especially at higher rpm. The engine will start and run without the high resolution signal, but a long crank complaint along with reduced performance could be noticed. The engine will not run without the low Figure 8-64, Optical Pick-Up Sensor resolution signal present. 9-46

47 Opti-Spark Ignition System The ignition system that uses the optical pick-up sensor is called Opti- Spark. Opti-Spark is a distributor ignition system that consists of the following components (Figure 8-65): Distributor housing Cap and rotor Optical position sensor Sensor disc Pickup assembly Distributor Driveshaft Figure 8-65, Opti-spark Distributor Assembly 9-47

48 Figure 8-66, 5.7L LTI Ignition System 9-48

49 Noteworthy Ignition Information There are several important considerations to remember where servicing the ignition system. The following list will help you in servicing the ignition system. The ignition coils secondary voltage output capabilities are very high - more than 40,000 volts. Avoid body contact with ignition high voltage secondary components when the engine is running, or personal injury may result. The crankshaft position sensor is the most critical part of the ignition system. If the sensor is damaged so that pulses are not generated, the engine will not start. Crankshaft position sensor clearance is very important. The sensor must not contact the rotating interrupter ring at any time, or sensor damage will result. Ignition timing is not adjustable. There are no timing marks on the crankshaft balancer or timing chain cover. Be careful not to damage the secondary ignition wires or boots when servicing the ignition system. Rotate each boot to dislodge it from the plug or coil tower before pulling it from either a spark plug or the ignition coil. Never pierce a secondary ignition wire or boot for any testing purposes. Future problems are guaranteed if test probes are pushed through the insulation for testing. Diagnosing Ignition system malfunctions can be categorized as either misfire or incorrect timing. Each requires a different approach to repair. Once diagnosis has lead to the ignition system, start looking for some telltale signs of the problem. In the case of misfires, look for the following: Plug wire disconnected Carbon tracking on coils and plugs Cracked insulators Rubbing plug wires Arcing to the block 9-49

50 Listen for the snapping of a strayed spark to the block, or use the time tested procedure of spraying down the components with water in an effort to provide alternate ground paths. The use of an ignition scope can be a valuable source of information concerning the condition of the ignition system. Misfires can occur at different times in the operation of the vehicle: all the time, at idle only, and under load only. These are all clues as to the possible source of the problem. Section 6 of the service manual usually includes a misfire detection chart that tries to isolate the source of the misfire. Part of this chart requires the use of an ST-125 that loads the ignition system by adding a specific resistance. It requires approximately 25kV to fire the ST Therefore, if the coil can consistently fire the ST-1 25, the coil is functioning normally. Another way to load the ignition system would be to perform the following Cranking Ignition Load Test: 1. Disable fuel delivery. 2. Set throttle to WOT. 3. Crank engine (for no more than 15 seconds at one time). Monitoring the ignition system on a scope while performing this test will show coil output well above 30 kv. Any secondary malfunctions normally will show up under these conditions. Incorrect timing typically is caused by an incorrect base timing setting. But systems such as the Knock Sensor (KS) circuit and some traction control inputs can cause the timing to be incorrect as well. The computer assumes that base timing has been set correctly. Therefore, it controls the timing assuming a proper starting point. If this is not the case, the timing the computer wants, and the timing that the engine is running at can be two different things. Of course, this is a moot point on El systems or "Net Build" systems such as the Opti-Spark where there is no base timing adjustment. Incorrect timing can cause sluggish operation, pinging, poor gas mileage, overheating, and high exhaust emissions. Therefore, proper base timing is critical. 9-50

51 Coil-On-Plug Ignition System In keeping with GM's most recent electronic ignition technology, the Vortec 4200 features a Coil-On-Plug Ignition system. This provides the highest energy spark and the most precise ignition timing. An integral coil and driver module is provided for each of the six cylinders (figure 8-67). Each coil has a power feed, a ground circuit and an ignition control circuit. The use of individual coil drivers allows coils more cooldown time between firing events and increases the available coil saturation time. The module mounting bolt acts as redundant ground path. Figure 8-67, Coil-On-Plug Ignition Coil Module Figure 8-68, Ignition System Schematic 9-51

52 Spark Plugs Platinum-tipped spark plugs (figure 8-69) are used for maximum performance and durability Powertrain Control Module Figure 8-69, Platinum-tipped Spark Plug The 4200 PCM, mounted on intake manifold (figure 8-70), is an advanced Tech 2000 with three 65 pin connectors. The PCM includes an internal knock sensor module. Figure 8-70, PCM Mounted on Intake Manifold 9-52

53 Dual Knock Sensors The Vortec 4200 uses two knock sensors (figures 8-71 and 8-72) mounted at the front and rear on the intake side of the engine. Figure 8-71, Dual Knock Sensors Figure 8-72, Knock Sensor Wiring 9-53

54 Crankshaft Position (CKP) Sensor As with other ignition systems, the PCM uses crankshaft (CKP) and camshaft position (CMP) sensors for precise ignition timing. The crankshaft position sensor is mounted in the left rear side of the block (figure 8-73). The reluctor wheel on the rear of the crankshaft has six, equally-spaced, notches and a synch notch. Figure 8-73, CKP Sensor Camshaft Position (CMP) Sensor The camshaft position sensor is mounted on the head, near the Camshaft Position Actuator Solenoid Valve. The cam sensor reluctor ring is actually part of the hub of the Exhaust Camshaft Position Actuator. The camshaft position sensor sends position information to the PCM during each revolution of the camshaft. Using the combined signals from the crankshaft and the camshaft position sensors, the PCM can determine engine position with great accuracy. If either the crankshaft or camshaft position sensor signal is lost for any reason, the engine can run using the remaining signal alone. The MIL will illuminate to indicate that a DTC has set. Figure 8-74, CMP Sensor 9-54