With Federal Emissions (Emissions Code D3)
POOR ACCELERATION, LACK OF POWERPreconditions
^ DTCs in Motronic 4.3 ECM absent.
^ DTCs in AW 50-42 TCM absent.
^ Engine is hot.
^ Fault is permanent.
Fault Sources
^ Timing retarded due to knock.
^ Defective rotor/distributor cap.
^ Damaged ignition leads.
^ Blocked air cleaner (ACL) or air intake.
^ Uneven compression.
^ Low fuel pressure.
^ Blocked exhaust system.
^ Faulty sensor signals.
TESTING PROCEDURE
Checking the Air Intake
^ Check the air intake in front of the radiator, air duct, ACL housing and cleaner insert for signs of blockage (leaves, paper etc).
If OK:
- Check the Mass Air Flow (MAF) Sensor.
If blocked:
- Rectify as necessary.
Checking the MAF Sensor
^ Ignition ON.
^ MAF sensor connected.
^ Connect a voltmeter between MAF sensor's connectors 2 and 4.
The voltmeter should show 0.1 - 0.2 Volts.
If the value is OK:
- Check the ignition leads.
If the reading is incorrect:
- Fault trace the MAF sensor. See: Testing By Trouble Code / DTC 1-2-1 MAF sensor signal.
Checking the Ignition Leads
^ Remove all the ignition leads.
^ Check the ignition leads for signs of damage, cracks or flashover.
^ Then measure the resistance of each ignition lead.
Resistance should read 1.5 - 4.5K Ohms depending on length, at 20° C (68° F).
If ignition leads are OK:
- Check the distributor cap and rotor.
If the ignition leads are not OK:
- Rectify as necessary.
Checking the Distributor Cap and Rotor
^ Remove the distributor cap.
^ Check the distributor cap/rotor for signs of damage, cracks and flashover.
If the distributor cap/rotor are OK:
- Check the spark plugs.
If the distributor cap/rotor are not OK:
- Replace all damaged parts.
Checking the Spark Plugs
^ Remove all the spark plugs.
^ Check if one of the spark plugs is lighter in color than the others.
If one plug is lighter than the others:
- This indicates that this cylinder is receiving too little fuel.
- Test with a new injector.
If all the spark plugs are the same color:
- Check the compression.
Checking the Compression
^ Carry out a compression test.
If the compression is OK:
- Check the fuel and residual pressure.
If the compression is uneven:
- Rectify as necessary.
Checking the Fuel and Residual Pressure
^ Check the fuel and residual pressure.
If the fuel and residual pressure are OK:
- Check the Engine Coolant Temperature (ECT) Sensor.
If fuel and residual pressure are not OK:
- Rectify as necessary.
Checking the Engine Temperature
^ START the engine and let it run at idling speed.
^ Read the ECT parameter.
Engine coolant temperature should be approx 80 - 105°C (176 - 221°F), when the engine is hot.
If the value is OK:
- Check retardation resulting from knock.
If the reading is incorrect:
- Check the ECT sensor.
Checking the Engine Coolant Temperature Sensor
^ Ignition ON.
^ Connect multimeter P/N 9996525 to temperature box P/N 9995281 and ECT sensor P/N 9995282.
^ Carefully take the cover off the expansion tank.
CAUTION: The water may be extremely hot.
^ Disconnect the hose between the rear of the engine and the radiator.
^ Insert the ECT sensor into the hose.
^ Refit the hose and expansion tank cover.
^ START the engine and let it idle.
^ Check that the Scan Tool (ST) shows the correct engine coolant temperature. There may be a difference of a couple of degrees owing to the location of the ECT sensors.
If the ST shows the correct engine coolant temperature:
- Check the engine cooling system.
If the ST shows the incorrect engine coolant temperature:
- Replace the ECT sensor.
Checking Timing Retardation Due to Knock
^ START the engine.
^ Test drive the car on the road and watch parameter "KN.IGN.RET".
^ If timing retardation due to knock constantly exceeds 10° while the car accelerates poorly or lacks power, it is probably because of this timing retardation.
If the timing retardation constantly exceeds 1O°:
- Proceed to: Checking for Knock section below.
If timing retardation does not constantly exceed 10°:
- Connect the break-out box.
Connect the Break-Out Box
^ Connect the break-out box and check the ground connectors.
^ Connect the ECM.
^ Check all the signals to and from the ECM.
Checking for Knock
^ Abnormal knock may be due to any one of the following reasons (which are not listed in any particular fault tracing order).
Oil Carry-Over
Combustion will be poor, resulting in knock, if the engine draws in oil through the crankcase ventilation system (possibly due to high oil level in engine).
Defective Spark Plugs/Ignition Leads
May cause poor combustion, resulting in knock.
Detective Distributor Cap/Rotor
May cause poor or faulty combustion, resulting in knock.
Loose/Defective Knock Sensor
May provide the ECM with faulty knock-related information.
Incorrect Fuel Grade
May cause poor combustion, resulting in knock.
Extremely High Engine/Air Temperature
May cause poor combustion, resulting in knock.
Incorrectly Adjusted Camshafts
The intake and exhaust valve opening times will be incorrect if the camshafts are incorrectly adjusted. The timing will also be faulty since the distributor is mounted at the rear of the camshaft. This may cause poor or faulty combustion, leading to knock.
Mechanical Knock
Mechanical knock may also be caused by worn mechanical components resulting in excessive bearing play, excessive piston clearance, valve rattle (faulty hydraulic tappets).
Checking the TWC and Exhaust System
^ Check the TWC and exhaust system for signs of blocked components.
^ Replace blocked components if necessary.