P0305
MISFIRING, CYLINDER 1, 2, 3, 4, 5 OR 6
Fault Symptoms.
CHECK ENGINE lamp (MIL) on.
Lumpy running while misfiring.
Any other diagnostic trouble codes.
Conditions.
During the course of each cylinder's powerstroke the rotational speed of the crankshaft increases temporarily. This gives rise to momentary increases in pulse frequency from the crankshaft position sensor. These frequency changes are evaluated by the control module and any misfiring is recorded.
How large a proportion of misfires is required for exhaust emissions to reach illegal levels or for the catalytic converter to be damaged is specified in a load and rpm dependent matrix in the control module's memory.
A diagnostic trouble code will be generated if the number of misfires exceeds the matrix figure.
Diagnostic Help.
The cause of the misfiring could be low fuel level in the tank. If this is the case, it will be indicated by diagnostic trouble code P1585 also being generated.
The injectors and ignition coils can be activated with the ISAT scan tool.
- Select "ACTIVATE".
- Select "INJECTOR 1" (2, 3, 4, 5, or 6).
- Select "IGNITION CYL 1-4" (2-5 or 3-6).
The cause of the diagnostic trouble code could be:
^ a detective spark plug, HT lead or ignition coil
^ a defective/clogged injector
^ poor compression in basic engine.
Check The Wiring.
Intermittent faults may occur as a result of temporary short circuits and breaks in the wiring. Jiggle the wiring at several points and in different directions to ascertain whether the wiring harness, including any connectors, is causing the trouble. Observe the multimeter, ISAT scan tool or test lamp while doing this.
Diagnostic Procedure.
1. Check other diagnostic trouble codes in the Motronic system Use an ISAT scan tool to obtain readouts of all diagnostic trouble codes.
Does the ISAT scan tool show any of the following diagnostic trouble codes?
^ P1585
^ P1213-P1230
^ P0300 together with at least two of the following diagnostic trouble codes: P0301, P0302, P0303, P0304, P0305, P0306. In such case, proceed as described for P0300.
YES: Continue fault diagnosis according to the diagnostic procedure for the relevant diagnostic trouble code.
NO: Continue with point 2.
WARNING: The electronic ignition system generates charges of up to 40,000 volts. Such voltages may prove fatal to persons with a weak heart or those who are fitted with a pacemaker. Therefore, treat the ignition system with great respect and take all necessary precautions.
2. Check the performance of the ignition coil module
- Install a test spark plug, part No. 86 11 386, in the relevant cylinder. Use a new HT lead.
- Connect the spark plug to ground using test cable assembly 86 10 867.
- Turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "IGNITION CYL X-Y".
The command activates the ignition coil at a frequency of 0.5 Hz for 30 seconds.
- Check that the activated spark plug produces a spark.
Is a spark produced?
YES: Continue with point 3.
NO: Continue with point 4.
3. Check the relevant HT lead
- Install a test spark plug, part No. 86 11 386, in the relevant cylinder. Use the existing HT lead.
- Connect the spark plug to ground using test cable assembly 86 10 867.
- Turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "IGNITION CYL X-Y".
The command activates the ignition coil at a frequency of 0.5 Hz for 30 seconds.
- Check that the activated spark plug produces a spark.
Everything OK?
YES: Continue with point 5.
NO: Change the relevant HT lead. Then continue with point 8.
4. Check the relevant control module output to the ignition coil module
- Unplug the ignition coil module's 4-pin connector.
- Connect the test lamp to:
^ pins 4 and 3 (cyl. 1-4)
^ Pins 4 and 1 (cyl. 2-5)
or
^ pins 4 and 2 (cyl. 3-6)
- turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "IGNITION CYL X-Y"
The command activates the appropriate ignition coil at a frequency of 0.5 Hz for 30 seconds. The test lamp should flash.
Test lamp flashing?
YES: Change the ignition coil module and continue with point 8.
NO: Rectify the lead in question and proceed to point 8.
5. Check the spark plugs
- Remove the relevant spark plug and check its condition visually.
Is the plug OK?
YES: Continue with point 6.
NO: The electrode gap is wider than 1.4 mm or is otherwise obviously wrong:
Change the plugs and continue with point 8.
6. Check the compression
- Carry out a compression test on the relevant cylinder.
Is the compression OK?
YES: Continue with point 7.
NO: Continue fault diagnosis in the Basic Engine.
7. Check the fuel flow capacity of the relevant injector
- Check the flow capacity. Testing and Inspection
Is the flow capacity OK?
YES: Continue with point 8.
NO: Change the injector. Then continue with point 8.