Fault Diagnosis, Poor Performance

FAULT DIAGNOSIS, POOR PERFORMANCE
General fault diagnosis for poor performance is difficult to carry out. However, a number of tips are given below.

1. First read out any diagnostic trouble codes in Trionic and take remedial action if necessary.

2. Check the basic charging pressure and max. boost pressure, and use an ISAT to check that the pressure sensor value corresponds to that of the pressure gauge.

NOTE: The engine only has max. boost pressure in 3rd, 4th and 5th gears (manual transmission).

3. Check fuse 24 to the boost pressure control valve. If the fuse is blown, first check the resistance of the valve.

A fuse that is too strong combined with a short-circuited valve can interfere with the ECM.





4. Faults in the basic engine, intake, exhaust or turbo systems can be easily detected.

Disconnect the hose to the wastegate. At wide open throttle, the pressure switch function must operate before approx. 3000 rpm. If so, faults in the above system can probably be ruled out. Activate "RESET BOOST PRESSURE" with an ISAT after this test.

5. Leaks between the compressor outlet and throttle body or in the by-pass valve or its regulating hose cause low boost pressure. Activate "RESET BOOST PRESSURE" with the ISAT after repairing the leak.





6. A fuel flow that is too low from the fuel pump or through the injectors is noticeable when driving at wide open throttle.

Connect an ISAT and read off the voltage in the oxygen sensor.

When driving at wide open throttle, this must be >0.5 V. If so, faults in the above systems can probably be ruled out.

7. If the ECM for any reason initiates basic charging pressure, this can be observed using an ISAT. Select READ FUNCTIONS" and the "BASIC CHARGING PRESSURE" command,

When driving at wide open throttle, the ISAT will show the cause, if any. If the ISAT shows that knocking is occurring, the cause may be poor fuel quality.

8. A subjective assessment that the car's performance is inadequate may be reinforced by too low a value being shown on the pressure gauge of the main instrument. Carry out adjustment of pressure gauge using an ISAT if necessary.