ATASA 5 TH Study Guide Chapter 31 Pages 922 948 47 Points Please Read The Summary
1. Troubleshooting EFI systems requires step by step test procedures mostly due to the many interrelated components and sensors. Computer Systematic Automatic
2. The vast majority of complaints about driveability, performance, fuel mileage, roughness, hard starting or no starting are due to the computer itself (PCM). True or False
3. Sensors are often condemned as defective when the real problem is the engine mechanical condition (known as base engine ) or the wiring to & from the sensors and the PCM. True or False Note: Always verify Base Engine operation before condemning sensors
4. Before testing EFI & EEC systems verify that the, & systems are functioning properly. Check all fuses connections. Verify MIL operation. The engine should be in good condition, with a quality supply that is not contaminated. Battery, Starting, Charging Mechanical, Fuel A scan tool alone cannot pin point problems with every little wire or connection or even every sensor A thorough working knowledge And proper use of the DMM is a necessary for troubleshooting
The battery, charging & starting systems, fuel system, vacuum lines, oil & coolant levels, thermostat operation, spark timing and the quality of the fuel all have a direct influence on how the electronic engine control system functions.
5. Sources of heat or sparks that could ignite fuel must be prevented. True or False
6. The EFI system must have good communication with the (Controller Area Network). MAN CAN TAN
7. The absence of a DTC means the fuel system is operating normally. True or False
8. Observing with a scan tool is a good starting point when diagnosing EFI systems. Fuel Trim Fuel Rim Fuel Brim
9. Lean engine conditions result in FT. Rich engine conditions result in FT. A cars computer (PCM) can make adjustments to the amount of fuel delivered to it's engine by varying the amount of fuel trim given to an injector pulse. Fuel trim is a percentage of positive or negative correction of fuel delivered, and it is used to keep the optimum fuel ratio to air. Short Term Fuel Trim (STFT) is based off of the Oxygen Sensors reporting of the current Air:Fuel ratio. Long Term Fuel Trim (LTFT) is used by the PCM to keep the STFT as close to zero as it can. These Trims are reported on a per engine bank basis. http://www.obd2scanners.com/ http://www.youtube.com/watch?v=y4eayyi67cw Positive, Negative Negative, Positive
10. V type engines will have a Bank 1 & Bank 2 HO 2 S and Bank 1 & Bank 2 Fuel # s. Trim Rim Brim PCM
11. An oxygen sensor can show a False Lean reading due to a cylinder. Campfire Re fire Misfire
12. If a HO 2 S response & cycling is slow, the sensor is called and should be replaced. Motivated Lazy Achiever
13. HO2S voltage stuck low results in fuel trim being. (+%) (lean exhaust = rich command) Richened Neutralized Leaned Blue Line = Normal Lavender Line = Lean Exhaust
14. HO2S voltage stuck high results in fuel trim being out. ( %) (rich exhaust = lean command) Richened Neutralized Leaned Blue Line = Normal Red Line = Rich Exhaust
15. Air that is unmetered, unmeasured or unaccounted for by the MAF causes a A/F ratio. Rich Neutral Lean
16. ratio sensors are different than oxygen sensors. They will display 2.4 to 4.0 volts. Oil Air Air Fuel Air Exhaust
The operating principle of a titania lambda sensor is entirely different from that of a zirconia lambda sensor. A titania lambda sensor works like a coolant sensor. It changes resistance as the air/fuel ratio goes from rich to lean; but instead of a gradual change, it switches very quickly from low resistance (less than 1000 ohms) when the mixture is rich to high resistance (over 20,000 ohms) when the mixture is lean. The input end of the titania sensor is fed from a fixed 1 volt supply, and the output end is pulled towards 0 volts by a fixed resistor. As the resistance of the titania sensor varies, so does the voltage at its output. When the fuel mixture is rich, the resistance of the sensor is low and so its output voltage is high. When the fuel mixture is lean, resistance shoots up and the voltage signal drops.
17. An air fuel sensor voltage INCREASE with a lean exhaust & DECREASE with a rich exhaust. Zirconia Sensor Titania Sensor When the fuel mixture is rich, the resistance of the sensor is low and so its output voltage is high. When the fuel mixture is lean, resistance shoots up and the voltage signal drops.
18. Peak heater amperage of an A/F sensor can be checked with Mode on the scan tool. (< 6 amps) $02 $04 $06
19. An air leak after the sensor will cause an overly lean A/F ratio & positive fuel trim #. IAT MAF ECT
20. Never soak or immerse the to clean it. Use a special MAF spray cleaner. IAT MAF ECT
21. If the MAF hot wire is dirty, check the relay or observe the burn off cycle. Burn off Turn off Rip off
22. Vacuum leaks in a MAP speed density system can be verified by watching counts. (counts are steps open from the closed position) IAC MAP MAF
The number of counts indicates how many steps out from the closed position the IAC is positioned at to by pass air for idle
23. Throttle, IACs, and intake manifold runners may need to be cleaned of deposits. Plates & Bores Angles Angels
24. fuel pressure can cause no start or poor run conditions. High fuel pressure = rich run.restricted return line too. Low Medium High
25. A injector can be diagnosed with a warm engine shut off, an exhaust analyzer probed into the intake plenum area. A high HC reading that does not drop indicates injector leaks. Short Leaking Clogged
26. An injector circuit can be checked for voltage switching with a light or logic probe. Noid Thyroid Droid
27. Injector coils can be tested with an ohmmeter for & opens. tests will help identify a restricted injector. A stethoscope can also be used to listen for the click. Shorts, Bleedown Blockage, Bleedown Leaking, Bleedown
28. A lab scope can be used to closely observe injector waveforms & ramps. Resistance, Current Voltage, Current Wattage, Current
28. A lab scope can be used to closely observe injector waveforms & ramps. Check the Vertical Axis Resistance, Current Voltage, Current Wattage, Current
Be able to sketch an injector scope pattern and label the points of turning on, turning off, the inductive kick, and the pulse width or on time. Inductive Kick Charging Voltage On Zero Volts Pulse Width (on time) Off
Inductive Kick Charging Voltage On Zero Volts Pulse Width (on time) Off If Injector does not pull down to zero line, There is a ground side voltage drop either in the PCM or the injector circuitry.
29. Injectors can be by running a chemical through them to dissolve deposits. Cleaned Deodorized Sanitized
30. During cleaning procedures, cleaning pressure should be about psi under fuel system psi. 5 psi 20 psi 50 psi
31. After cleaning injectors, drive the vehicle to allow memory to relearn trims. Adaptive Reactive Permanent
32. When replacing injectors, all o rings should be lightly lubricated with engine. Coolant Oil Fuel
33. After fuel rail R & R and injector replacement start the engine & check for. Ohms Volts Leaks
34. An electronic throttle control system has 2 sensors, 2 sensors, and 2 driver circuits for the throttle actuator motor one that opens the plate & one that closes it. TP, APP TP, BPP TP, FTP Accelerator Pedal Position Sensors Throttle Position Sensors
35. mode on electronic throttle control holds the throttle open slightly with a spring. In the case of a failure this allows the vehicle to run at a fast idle & pull off of the road. Fail Safe Tennis Shoe Limp Home
36. If the battery is disconnected & reconnected, the PCM will go through an idle procedure automatically. If the PCM is replaced, the relearn procedure may be more extensive. Re Calibration Re Learn Re Tool
37. The (Idle Air Control Motor) automatically adjusts idle speed as conditions demand on SFI. IAC IATN IAT
38. Scan tools can bi directionally control the IAC & pintle to verify operation. Motor Armature Rotor
Diagnostic Trouble Codes are read with scan tools or on some OBD I vehicles, can be read by counting the blinking MIL when put into the field service mode.
GM Ford Dodge Toyota
Lean exhaust due to Large amounts of oxygen produces Low voltages at the EGOS. (.1 to.4).450 volts or 450 millivolts is the middle range for an EGOS. It s also the PCM generated voltage during open loop until the HO2S becomes responsive.
Rich exhaust due to small amounts of oxygen produces high voltages at the upstream HO 2 S. (.5.9 volts ) or (500 to 900 millivolts)
The activity or switching of an oxygen sensor can be best monitored with a Lab Scope. A slow responding or lazy EGOS is hard to detect with a scan tool lab scopes rule for this! (also called DSO s Digital Storage Oscilloscopes
Injector pulse width is adjusted in response to upstream HO2S readings. This adjustment to injector on time, expressed in percentage of fuel added or subtracted from the norm is known as fuel trim. STFT = integrator & LTFT = block learn
Block learn & integrator have a normal # of 128 with a # closer to 256 meaning the PCM is richening the pulse width and a # closer to 0 meaning the PCM is leaning the A/F ratio. Block Learn is Long Term Fuel Trim Integrator is Short Term Fuel Trim
A restricted injector can cause a lean misfire, resulting in EGOS stuck low, rich command from the PCM, a CO problem, and a HC problem due to lean misfire condition in the cylinder. (tough logic to follow!)
An injector balance test is done using a pressure gauge & an EFI pulse tester. Injectors can also be diagnosed by listening to their operation with a technician s electronic stethoscope.
Note: Too much alcohol ethanol in fuel may cause lack of power, stumble or hesitation on acceleration, frequent engine stalling & no start conditions.
EFI fuel pressure is checked with a gauge connected to the shrader valve, Which is usually located on the fuel rail.
Some EFI systems, especially TBI types, use a pulsation damper to control fluctuations. The fluctuation is due more to the single injector opening & closing than the fuel pump operation.
Remember: A vacuum sensitive fuel pressure regulator increases the psi as the engine vacuum drops more psi @WOT!
Be able to explain in your own words why engine vacuum is lower under heavy acceleration or WOT: Vacuum is caused by the intake strokes pulling against a closed throttle plate. If the throttle plate is open for acceleration, the vacuum is more like atmospheric pressure. A vacuum gauge reading is a comparison of engine pressure to atmospheric pressure. With the throttle plate open, the pressures are closer to equaling each other. This causes a closer to zero pressure difference, or in other words zero vacuum.