Performance Down

FAULT DIAGNOSIS, PERFORMANCE DOWN

General fault diagnosis procedures for poor performance are difficult to recommend.
However, here follow some useful hints and advice.

1. First obtain readouts of any diagnostic trouble codes stored in the Motronic system and deal with them.

2. Check the operation of the variable intake manifold.
Start the engine and then switch it OFF.
Activate the two flaps by means of the Scan Tool.
- It should be possible to activate each of the two flaps twice by means of the accumulated vacuum.

If this is not the case, check whether the fault is electrical or mechanical or whether vacuum is absent.

3. Too little fuel from the fuel pump or through the injectors will be noticed when driving at wide open throttle.
Connect a Scan Tool.
Select "READ FUNCTIONS".
Select "REAR OXY SENSOR" OR "FRONT OXY SENSOR".
Read the voltage from one of the oxygen sensors.
- When driving at wide open throttle it should be >0.5 V.

If this is the case, a fault in the above systems can probably be ruled out.





4. Late ignition results in loss of power.
Use a Scan Tool to check how much the control module retards the ignition if knocking occurs when driving at wide open throttle.

If it exceeds 6° for a lengthier period of time, poor-quality fuel may be suspected as the cause.

Other causes may be bad or defective spark plugs or too little fuel from the fuel pump or through the injectors.
Also bear in mind that abnormal vibration caused by mechanical faults in the engine or its auxiliaries may give rise to spurious knock indication.

5. A rough indication of the engine's cylinder balance can be obtained with the Scan Tool.
Turn off one injector at a time to determine whether any cylinder is down On power.

If this is suspected a compression test must be carried out.