Index Emission Testing with Modern European Equipment 01) Introduction...2 02) Petrol Emission testing...3 02a) Catalytic converter...4 02b) Oxygen sensor...4 02c) E- OBD vehicles...5 02d) Non OBD vehicles...5 03) Emission tester...6 03a) Preparations for the emission test...7 03b) Calibration...9 03c) Leak check...10 04) Hook up...12 04a) RPM with DiSpeed...12 04b) RPM with Trigger clamp...16 04c) RPM through OBD connector...18 04d) Engine temperature sensing...19 04d) E-OBD temperature sensing...21 05) Official 2 speed idle Emission testing...25 05a) Outside testing limits...32 05b) Official 2 speed idle Emission testing with E-OBD compliant vehicle...34 06) Diesel emission testing...37 06a) Engine temperature...37 06b) Engine speed...38 06c) Official Diesel emission test...40 1
01) Introduction. The following presentation will be based around the AVL DiX 480 series emission testers. It is meant to give you a good insight into the current European emission testing protocol, and how the operator and equipment deals with the tests. AVL DiX 650 with Scantool, Oscilloscope, 5 gas petrol emission tester and Diesel Opacity tester. 02) Petrol Emission testing Emission testing in all European countries and many countries outside the European union is done using a two speed idle test. The two speed idle test is used to simulate congested urban traffic (idling in traffic jams) and low load (<20% throttle), running as what would happen in built up areas. Urban areas have the highest density pollution, so pose the greatest health cost risks to society. Admittingly, with small throttle openings a low volume of exhaust gas is passing through the catalytic converter, so even a worn (coated) converter or a slow oxygen sensor would still produce good emissions at the tail pipe. 2
02a) Catalytic converter The cold cylinder walls of the combustion chamber quench the flame on the fringes of the combustion area, affecting the chemical reaction between the fuel (Hydro Carbons like Octane C 8 H 18 ) and oxygen (O 2 ). This happens under all circumstances, hot and cold, low load and high load. An oxygen storage catalytic converter captures unused oxygen out of the emissions and reduces NO x to N 2 and O 2. The stored oxygen will react with the partially burned fuel (CO) and unburned fuel (HC s of various combinations) when the catalyst is over approximately 300 C. The HC s and CO s together with the oxygen (O 2 ) will be converted in the cat into H 2 O and CO 2 under the most common conditions: operating temperature and part load. On Euro 3 designed systems the emissions should be reduced by the cat at idle and part load. Euro 4 rules tightens up the cold start high emissions by having a quick response system, one that warms up quicker so that only during approximately the first 20 seconds or less emissions are more or less uncontrolled. A catalytic converter (cat) can get coated by for example fuel additives, prolonged rich running of the vehicle, oil consumption and by sediment (gum) from the fuel, loosed up by for example injector cleaner added to the fuel. A cat can get mechanically damaged by engine misfire (only a few seconds of medium load full misfire is enough) or by for example hitting objects on the road. A worn or else damaged cat has a lesser conversion surface area. During low load the lesser active surface area will still convert the relative small amount of HC s and CO s with the oxygen (O 2 ) into H 2 O and CO 2. During high load running (throttle angle >50%) the converter gets flooded with either too much oxygen or too much rich mixture. The converter will cool down (the flame will extinguish) and the harmful HC s and CO gasses will pass straight trough. 02b) Oxygen sensor The oxygen sensor will get coated over a certain period of time. The active surface will be harder to reach for oxygen, so the ECU will over compensate before it sees that the mixture status has changed. This will result in slower mixture changes, which will result in a cat that gets flooded with too much rich and too much lean mixture. Again at part to high load the cat will cool down and the harmful HC s and CO gasses will pass straight through. 3
02c) E- OBD vehicles E-OBD vehicles were built from Jan 2000 (new models), and Jan 2001 existing models. European On Board Diagnostics era vehicles have a cat downstream oxygen sensor. This sensor will start responding when the cat looses its temperature. The ECU of such vehicles is programmed to see the rear oxygen sensor cycle during warm-up for a set period of time, and than more or less flat line. Small deviations are allowed as long as they stay within certain voltage parameters. Removing a cat or replacing the cat with one of a different volume or with different warm up characteristics (e.g. for example substrate thickness) will certainly result in a fault code with a limp home situation triggered. Limp home is usually reduced power output to about 60%. E-OBD vehicles are NOT fail safe. An E-OBD vehicle has more closed loop systems and check functions. On E-OBD vehicles if something goes wrong in the mixture preparation process within the programmed parameters the up and down stream oxygen sensors will be happy and letting high emissions through. There seems to be a misconception that E-OBD vehicles do not need to be emission tested. This is largely based on the fact that in some European countries (Germany and next year more countries will follow) an EOBD scantool needs to poll the ECU for emission related fault codes before the emission test. Also these vehicles have during the emissions test their engine temperature and RPM measured via the E-OBD connector, which is a great time saver. 02d) Non OBD vehicles Temperature measurement For non OBD Petrol vehicles (which includes vehicles up to 2000 or some even newer, like Australian sourced vehicles) the temperature of the engine needs to be measured with an oil temperature probe inserted into the dipstick tube. The oil temperature needs to be greater than 70 C before the test can commence. The reason for including the temperature pick up in the test is that a cold piston will have high HC s and high CO s as result. The combustion will not extend into the fringes (cold areas) of the cold combustion chamber. Therefore a large number of vehicles could fail the test. RPM measurement The engine speed needs to be measured during an emission test. In many early to late 90 s engine management systems the mixture control will go into open loop at idle. Also every engine management system will enter into a different mixture/ emission control cycle as soon as the accelerator is 4
released (idle). As stated before most urban vehicle emissions are emitted during idle and low part load. The emission tester needs to recognise the operating status of the engine, so that it can produce an objective two speed idle emission test result. The tester will indicate to hold the engine speed between 2500 and 3500 RPM and will wait until it senses that the engine is between those two speeds, this is called high idle. The high idle emission values are being stored if the engine speed is between those two values for a period of time. After the high idle test is finished an idle test has to be performed. The emission tester will sense that the RPM is low, between 500 and 1000 RPM and that the idle speed is stable for a period of time. The emission tester will store the idle speed emission results. On vehicles that are in a poor state of repair it is some times impossible to hold the RPM at a stable level. A slow responding (worn) oxygen sensor, incorrectly adjusted TPS, or seized idle control motor are just a few examples that will cause unstable engine speeds. These vehicles inevitably will fail the emission test. 03) Emission tester The emission tester will have to be stabilised and zero calibrated. Three gasses of the emissions are measured with an infrared gas bench. For this reason the emission tester has to go through a warm up procedure. The most efficient for any workshop is to turn the emission tester on in the morning and let it run all day. The emission tester is ready to go and maintains a stabilised temperature constantly. The side effect is that it will cause moisture resulting from changing ambient temperatures to settle down on the tester internals. 5
03a) Preparations for the emission test Switch the tester on and let it go through its automatic warm up procedure of several minutes. During the warm-up and stabilisation 6
the tester will regulate the current to the IR light source so that light source intensity fluctuations do not have an effect on the actual emission values. 7
The emission values of HC, CO and CO 2 gasses are measured by light absorption in the IR spectrum. The sensed quantity of light is a measure of the volumetric percentage of gas or the molecular percentage of HC s. The Oxygen and Nitrous oxides are measured with galvanic cells. The conductivity of the gas is a measure of that volumetric quantity of gas the Oxygen sensor is sensitive to oxygen and the NO x cell is sensitive to mainly NO. During the HC residue check the tester will draw clean air through the test probe to see if perhaps carbon contamination has fouled the sampling tube. This is to prevent incorrect readings of HC s. 03b) Calibration During the warm up the tester will perform an automatic zero calibration. The pump will draw clean air filtered through an active carbon filter through the test bench. The air entering the tester is now used to reset the zero measuring point of all measured gasses and the 20.8% vol oxygen content point. The zero calibration filter is a carbon canister that takes any HC s out of the atmospheric air surrounding the emission tester. A contaminated or saturated carbon canister will shift the zero points. An incorrect zero calibration will have incorrect measurement values as results. The carbon canister needs to be replaced under normal circumstances every 12 months. Carbon canisters can be the cause of problems when for example the tester is placed near a high source of HC s like an open vat of fuel or paint, or when the canister has been used to feed the tester with calibration gas or emissions. The tester will return incorrect readings when the canister has been removed. Carbon canisters cannot be recycled by for example blowing air through them in reversed direction. Calibration graphs: A = incorrect offset calibration (service dealer only!) B = Correct calibration C = Incorrect zero calibration (e.g. carbon canister) 8
Every twelve months the tester s offset has to be calibrated by an authorised calibration facility. Many testers faults are the result of incorrect calibration or the lack of calibration. All testers will have some drift over time. Drift is where the actual measured gas quantity is not displayed correctly anymore for a multitude of reasons. The drift needs to be calibrated away to be sure that the actual displayed value is true, with certified calibration gas. 03c) Leak check The tester will perform a leak check in official measurement mode to make sure that the gasses sampled are not diluted with air, upsetting the lambda and gasses figure. The tester will prompt the user to close the probe. A piece of silicon hose is usually good enough. The tester will draw vacuum with its gas pump. The pressure is being monitored after the pump has been switched off. 9
Leak test being executed After the tester has seen that the pressure in the pneumatic circuit has not risen outside parameters it will class the circuit as okay. These checks will set the tester up for the day. 10
04) Hook up Select what type of probes need to be used to connect to the vehicle. 04a) RPM with DiSpeed The DiSpeed is an RPM sensor that is attached to the engine with a magnet. The sensor measures vibrations and sounds. The electronics will filter out one repetitive pulse and take that as one revolution. 11
The LED in the magnet is red when the automatic calibration has not been performed yet, or when there are no vibrations (engine off). As soon as the sensor picks up a pulse its LED will turn orange. 12
A single point calibration has been performed and the tester display will already indicate RPM. To have accurate RPM s displayed a two point calibration is necessary, for this the engine speed needs to be raised to about ¾ of maximum speed. The LED will turn green when the calibration has been completed. It is important to know that no cylinder quantity selection is necessary and that the calibration process takes only about 10 seconds or so. 13
Signal filtering of the AVL DiSpeed. 14
The screen will display the engine speed. Selectable are 4 wheel vehicle and 2 wheel vehicle (motor bike) as the sensitivity (engine inertia) for both vehicles are very different. In this screen a different type of RPM measurement can be selected. 04b) RPM with Trigger clamp For example Trigger clamp. You need to connect a pick up lead to the tester: And you need to connect an inductive pick up to the engine. You can connect to an ignition HT lead. 15
Or to a coil primary wire while the earth clamp is connected to ground: All you have to do is identify the type of coil and amount of pulses per revolution. You will be able to see the RPM in the screen when the engine is running for confirmation. 16
04c) RPM through OBD connector Also from this screen you can select to have the engine speed taken by serial communication from the vehicle s E- OBD system (if the vehicle is E-OBD compliant). This is by far the most modern option, as it means that you can leave the bonnet down. You need to connect the integrated DiOBD880 scantool to the serial connector of the vehicle: And select in the screen the OBD option. 17
Again the engine speed can be seen in the screen. - Also an optical sensor, where a reflective surface needs to be attached to the crankshaft. The light sensor will trigger when the reflective surface returns the light beam. This option is often used when access to the crankshaft pulley is easy. - A brand specific special TDC connector can be chosen from this screen. This option is used mainly by franchise dealers like VW/Audi, BMW, Mercedes Benz, etc. 04d) Engine temperature sensing The emission tester needs to measure the engine temperature, to ensure consistent results. To be able to measure the engine temperature there are several options. Oil temperature sensor An oil temperature sensor can be connected to the emission tester The oil temperature sensor needs to be inserted in to the dipstick tube so that the tip of the sensor cable that contains a thermo couple touches the engine oil. For this the sensor s length needs to be adjusted. 18
Remove dipstick Adjust the length of the sensor, so that the sensor can t enter the engine too deep. Push the bung firmly onto the dipstick tube, so no air can enter the engine through the crankcase ventilation, upsetting the mixture. Select the type of temperature sensor if it differs from the last time when the emission tester was used. 19
In the screen the actual value can be seen, so you know the sensor is operational. 04d) E-OBD temperature sensing It is also possible to take the engine temperature from the vehicle s E- OBD system. This is providing that there are no electronic faults in the vehicle s temperature sensor circuit. Connect the DiOBD880 to the vehicle s diagnostic connector Select from the screen the OBD option if it was not selected during the previous test. 20
With F5 (connect) the scantool is prompted to establish communication with the vehicle and poll it for temperature data. While it is making connection with the vehicle and collectss data the above screen is displayed. 21
Once communication has been established, the actual value will be show in the screen for confirmation. Click F8 to carry on into the emission tester screen. Standard Emission Test The screen will show all relevant data, a tester with the NO measurement option included will show NO in the same screen. Display on the actual Digas480 emission tester. The values can be read and digested, they can be used for diagnostics and for testing after a repair. - The RPM shows a slightly elevated RPM, as if the engine is in warm up mode. - The engine temperature shows 63 degrees, confirming that the engine is not up to operating temperature yet. 22
- CO 2 of 14.8 vol% is a little low for a vehicle which is E-OBD compliant, but normal to good for an engine which is in its warming up phase. The cat might not be operational yet (too cold), and therefore the CO s,hc s and oxygen have not reacted with each other in the cat, yet as a result of the cold engine there will be an abundance of those gasses. - The O 2 of 0.81 vol % is a bit high, it shows that there is plenty of air that is unused (from the fringes of the combustion process) coming out of the engine, and flowing straight through the cold cat. - HC of 93 Parts Per Million (PPM) shows that there is unused fuel coming out of the engine and straight through the cold cat. The value is not excessively high, indicating that engine has passed the cold start enrichment stage but that the fringes of the combustion process are too cold. - A CO of 0.57 Vol % is the key indicator that the cat is not operational. - A Lambda of 1.017 indicates a slightly lean mixture, typical for an engine just coming of cold start enrichment. 23
05) Official 2 speed idle Emission testing. During official emission testing the type of vehicle needs to be entered so that the emission tester can use that data to select the correct type of emission test. Data source in manual mode means that you have to manually insert the vehicle details. The registration date (year of manufacturing) of the vehicle will determine the pass and fail standards. The Engine type will determine firstly if the Opacity tester or the gas analyser will be used. In this case the gas analyser will be selected. From the submenu, petrol engine you can select if the engine has; 1) A catalytic converter (cat), 2) A cat with E-OBD for getting the scantool ready for RPM and temp, 3) No cat, for older vehicles with lower pass and fail standards. After confirming the details the vehicle is entered in the memory of the tester, so that after the test the data of the vehicle gets used in the printout. On the menu of the screen you can now select the OM option, which stands for Official Measurement. 24
As soon as the official measurement is chosen the 4/5 gas analyser gets activated out of stand by mode. In most countries it is a legal requirement that an HC and leak check is being performed before every check, so the following will happen: The screen will prompt to close the probe. When the pressure rise is within limits the tester will show the passed message. After the leak check an HC test will check for hose contamination. After the HC check has passed the tester will automatically move to the next screen, prompting to insert the probe and to start the engine. 25
After a short stabilisation time the tester will indicate what it wants you to do. In this screen the tester prompts the operator to accelerate, while at the same time it shows which values are outside acceptable limits. The most important values to watch at this moment are the engine temperature and CO value. 26
The engine temperature (43 C) indicates that the engine is cold and that therefore the test would not be realistic. The CO figure of 4.81 Vol% indicates that the catalytic converter is not operational yet. From a large distance the Yellow arrow pointing to the right is always an indication that acceleration is required. When the required idle speed has been reached the blue square with the two yellow arrows will light up, indicating to hold the speed steady. The bandwidth of engine speed variation is indicated by the horizontal bar graph on the right hand side of the screen. A counter will start as soon as the RPM value falls with in the bandwidth, this is to show how much longer that the rev s need to be kept at that level. The rev s need to be kept constant to give the engine management the opportunity to stabilise the mixture after for example acceleration enrichment. The timer will reset if the RPM fall outside the bandwidth. 27
The tester will clearly indicate that the revs are outside the bandwidth. The counter has restarted and counts down again to let the emissions settle as soon as the RPM falls within the bandwidth. 28
After the counter has finished the emission gas values will be stored in the tester s memory, and the tester will indicate to decelerate to idle. The tester will show the idle bandwidth and live emission values. 29
It will show a message to hold the engine speed stable. Once the gas values are accepted to be stable the tester will carry on, which can be bypassed by the operator (F8). Automatically a report will be generated, and shown ready for a printout. Function Key F4 will activate the printing process. 30
05a) Outside testing limits When the emission values are outside of legal parameters the bad values will be shown in red. At raised idle the CO, HC and Lambda values are compared to standards. The mixture is too lean as one of the injectors is disabled. HC is low enough and the CO is low enough. At idle the Lambda is not monitored as many older vehicles enter open loop running at idle. 31
In the printout the fail levels will be shown in red. In this case the mixture is overly rich as a result of an airmass sensor problem. The CO indicates very rich and turns red. The HC s are high but not 32
outside parameters. The lambda figure shows very rich, but is not monitored at idle under the used test protocol. 05b) Official 2 speed idle Emission testing with E-OBD compliant vehicle. In the official emission testing selection menu where the type of vehicle that can be chosen the option exist to choose a vehicle with CAT and OBD. The tester sets it self up for the 2 speed emission test with the RPM and engine temperature measured via serial communication (scantool). After selecting the vehicle details the tester will prompt the inspector to check if the Malfunction indicator light is working, and to perform a visual inspection. 33
After clicking the next button (F8) the tester prompts the inspector to connect the E-OBD connector, and to insert the probe into the exhaust. An ecu readiness test and fault code check is then carried out before the official measurement commences. After which the same procedure (as with non E-OBD vehicles) needs to be completed, with the high idle and idle stabilisation of values. 34
In the Previous picture it is clear to see that this car is running very efficiently, and that the cat is working correctly. The CO value of 0.01 vol% is very low, indicating that the cat is working very well, reducing further an already very low CO reading. The HC of 8 PPM is also very low. Again the cat is reducing an already very low level of unused fuel. The CO 2 of 15.4 vol% is high, this means that the content of completely burned fuel in the emissions is high, indicating an efficient combustion process. The Lambda value of 0.999 indicates an almost stoichiometric mixture. This also indicates that the low CO and low HC are not the result of a lean running condition, verified by the CO 2 percentage and the lack of oxygen in the emissions (0%). 35
06) Diesel emission testing. Diesel emission testing is performed very differently from petrol emission testing. The Diesel emission tester check s the emissions opacity, by means of light absorption. 06a) Engine temperature. The engine needs to be up to operating temperature. The temperature of the engine needs to be measured during the emission test. To bring an engine up to operating temperature (oil temp of more than 60 C) can take, from cold, up to 4 minutes. Best is to have the vehicle tested straight after a test drive or when the vehicle is presented to the workshop hot from the street. Fuel is made out of Hydro Carbons (HC s). The average chemical formula for common diesel fuel is C 12 H 26, ranging from approx. C 10 H 22 to C 15 H 32. Air consists out of Nitrogen (N 2 +/- 79%) and Oxygen O 2 +/-20.8%). During the combustion process the Oxygen (O 2 ) from the air reacts with the Hydrogen (H) and with the Carbon (C) from the fuel. The ideal out come from this chemical reaction is: C 12 H 26 + O 2 + N 2 = CO 2 + H 2 O + N 2 + Heat How ever all conditions need to be ideal for this, the mixture, the mechanical condition of the engine, the temperature in the combustion chamber and the fuel quality. Cold cylinder walls of the combustion chamber quench the flame on the outside of the combustion process, affecting the chemical reaction between the fuel (HC) and oxygen (O 2 ). The HC will fall apart into H and C as a result of the pressure. The H will find O 2 and forms water, but the C (carbon) will exit the exhaust as black soot, it needs the high temperature to form a bond with oxygen. The carbon, which is a solid will bond together and forms particles. The particles are the cause of the black smoke we see from Diesel engines. The smaller the droplets of fuel entering the combustion chamber (common rail), the smaller the soot particles. The smaller the soot particles the greater the health risks. Particulate filters are the one way to reduce the amount of emitted particulates. The DPF will capture the particulates. The captured solid carbon flakes will be burned off when the filter pressure difference gets too great. The carbon reacting with oxygen forms CO 2, which is a gas, which exits the filter without any obstruction. Particulate emissions are higher on a cold engine. 36
06b) Engine speed. The engine speed needs to be measured during an emission test. The emission tester needs to recognise the operating status of the engine, so that it can produce a subjective snap acceleration emission test result. The construction of the Diesel injection mechanism requires that the accelerator gets depressed fully to get a full quantity of Diesel injected (minus the turbo compensation). The quantity of Diesel injected combined with the amount of air entering into the combustion chamber and the volatility of the process gives a representation of what will be happening on the road during most operating circumstances. Accelerating slowly will never achieve the full delivery of the injection pump, so a false pass could be the result on a true smokey vehicle. The tester will measure the time it takes to accelerate from a stable idle speed to cut off speed. The acceleration time will be compared from three tests ( acc. t.). It is virtually impossible to slowly accelerate the engine three times with the same acceleration time (for example to try to fool the test). The large difference in acceleration time will create in the tester a failed test result. Sudden deceleration of a Diesel engine as a result of its high compression can have a slipped timing belt as a result of the force on the belt being inverted and the belt tensioner now acts as an idler. A spring loaded or damaged hydraulic tensioner or a tensioner which is slack gives the belt room to move. Before a test is performed a visual check needs to be made on the state of maintenance of the engine. For example an oil leak from the timing belt cover weakening the timing belt, or a vehicle with an unknown maintenance record should have a disclaimer signed for the test or have the test skipped due to maintenance issues. The mechanical condition of the Diesel engine can have a huge impact on its emissions. In many circumstances it is more than one problem. Below is a short list of possible and common problems. Pre combustion chambers Cracked pre combustion chambers in the cylinder head disturbs the gas flow and mixing of Diesel with air. Poor combustion with high emissions is the result. Damaged piston crowns Damaged piston crowns as a result of for example valve interference disturbs the gas flow in the cylinder head and mixing of Diesel with air. Poor combustion with high emissions is the result. Low compression Low compression has low temperatures in the combustion chamber as result. Low temperatures cause a poor chemical reaction between air and the Diesel. A poor chemical reaction equals high emissions. Also 37
the intensity of the explosion on the piston is now reduced, to achieve the same road speed the accelerator has to be depressed further, increasing the emissions even further. Worn injectors A poor spray pattern from worn injectors create pockets of very rich mixture (unburned fuel in the exhaust) and pockets of very lean mixture which are not taking part into putting pressure onto the piston. The accelerator needs to be depressed further to make up for the reduced pressure on the piston. Altered fuel quantity Some DIY Diesel tuners think that they can better the engine by changing the fuelling of the engine. This is under all circumstances an increase of Diesel delivery, (with out timing compensation) this results in high emissions. Worn turbo seals The high speeds with which a turbo charger rotates demands high quantities of oil to lubricate the turbine shaft. The seals on that shaft are prone to wear. High quantities of oil will find their way into the combustion chamber when seals are worn. Engine oil does not have the same ignition characteristics as Diesel, plus it is un-metered fuel. The result is always high emissions. Air filter The air intake of a Diesel engine needs to be clean and un obstructed. The mechanical Diesel engine could create smoke under high airflow conditions as a blocked air cleaner restricts the airflow. The mechanical Diesel pump does not compensate for the quantity of air entering into the combustion chamber, it just assumes that all is well. Most electronic controlled Diesel engines measure the air quantity or the manifold pressure and adjust the injected Diesel quantity accordingly. An electronic controlled Diesel engine usually does not smoke as a result of a blocked air cleaner, it will just have a lack of high end power. Alternative Fuels An engine that is designed for a certain fuel of a certain viscosity will respond different with alternative fuels. Note for your information: It should be noted that not one manufacturer of Diesel equipment (Denso, Delphi, Bosch) allow Bio Diesel to be used in their equipment. Many horrible expensive repairs have been the result of using bio Diesel in modern Diesel engines. Some good results have been reported from using bio Diesel in older low pressure mechanical Diesel engines although the difference in viscosity has uncontrolled timing issues as result on a mechanical controlled diesel engine. 38
06c) Official Diesel emission test. After the vehicle is selected and the OM (official measurement) is chosen the tester will show to what limits it will test, this is country and engine type depending. 39
The inspector can choose the type of test (also country depending). a) One time test is just one measurement, its up to the inspector not to fool the machine by slowly accelerating. b) Quick test is a cycle of three tests. The machine will average the results of the three tests and will not look at acceleration time bandwidth. c) A complete test is where the machine will perform between 6 and 10 measurements. It will look at acceleration time and smoke bandwidth, to see if the inspector is making testing procedure mistakes. And also to check if for example sudden dislodging of oil from the intake manifold sends the average emission values over the limit. The tester will progress to the next screen: 40
The type of temperature sensor can be selected. - Manual input can be selected if there is no other way to test the temperature of the engine. You have to type the measured (with for example infra red) engine temperature in by hand. - Temperature sensor needs to be selected when the oil temperature sensor is being used in the oil dipstick tube (see illustration). - E-OBD lets the tester take the signal from the ECU via the connected scantool. 41
The tester will wait until the engine has exceeded 60 degrees before it allows the test to commence. A soon as the temperature has reached 60 degrees a timer will start (bottom RH corner), during this period the opacity chamber is stabilising. 42
The tester will monitor the engine s idle speed during a period of time, in order to store the idle speed in its memory. After the tester has memorised the idle speed of the engine it will ask for an acceleration to cut off speed. This to record into the memory the maximum engine speed. 43
The idle speed and cut off speed are memorised so that the tester can detect the time it takes to accelerate. The acceleration time will be measured from when the engine speed moves just over the recorded idle speed to when it reaches the recorded cut off speed. The acceleration time of each acceleration will be compared to make sure the testing is done consistently. To depress the accelerator slowly makes any Diesel smoke less than under full acceleration on the road. Fully accelerating without load simulates most operating conditions for a brief period of time, although on some electronic controlled Diesel engines the lack of vehicle speed signal puts it into a different fuelling mode, on some brands this seems done just to pass any future emission test. Any vehicle type approval takes the different emissions produced during a drive cycle and the emissions produced during a snap acceleration emission test into consideration. The snap acceleration test will therefore be still a good emissions indicator even on electronic controlled Diesel vehicles. 44
During the acceleration and deceleration the tester will clearly indicate what it expects from the operator. On this picture the tester wants you to hold the idle speed stable, the timer will indicate for how long. After which it wants to see a full acceleration to cut off speed, indicated by the arrow up. 45
In this screen it wants you to hold the engine at cut off speed for around 1 second. It then demands deceleration. 46
The display will show the test results. Explanation of values in the screen: 1) The sensed and recorded Idle speed (700 RPM) 2) The achieved Cut off speed (4690 RPM) 3) The Absorption coefficient or K value (0.35 m -1 ) 4) The Acceleration time, the time it takes to move from the idle trigger to the cut off speed trigger (1.3 seconds) 5) The Engine temperature (70 C) as recorded by the temperature probe or via the E-OBD connector. After the test cycles are completed the tester will proceed to a print function or in some countries it will establish contact with for example the ministry of transport data base via the internet, to report the emission results linked to the licence plate of the vehicle. Printed, the results looks as follows: 47
The average K value is calculated and results of each acceleration are printed. The tester also clearly indicates a pass or fail result. 48