Poor Performance

FAULT DIAGNOSIS, POOR PERFORMANCE

Prior Condition
No diagnostic trouble codes


DIAGNOSTIC PROCEDURE
General fault diagnosis procedures for poor performance are difficult to suggest. Some useful hints and advice are given below, however.

1. Checking The Operation Of The Pressure Sensor
Turn the ignition switch to the ON position and then back to the OFF position.
Select "READ FUNCTIONS".
Select "INTAKE PRESSURE".
The Scan Tool should show a reading of about 102 kPa

NOTE: The reading is dependent on barometric pressure.

First build up a pressure of 0.6 bar and then create a vacuum of -0.6 bar. Use a pressure gauge and a pressure/vacuum pump.
The Scan Tool should show readings of 160 ±5 kPa and 40 ±5 kPa (slightly lower readings might be obtained at high altitudes).

If any reading is incorrect, change the pressure sensor.

NOTE: Boost pressure is limited in 1st gear.

If boost pressure is low, see low boost pressure. Low Boost Pressure

2. Checking The Fuel Flow
If the flow of fuel from the fuel pump or through the injectors is too low, it will be noticeable when driving at wide open throttle.
Connect the Scan Tool.
Select "READ FUNCTIONS".
Select "OXYGEN SENSOR".

At wide open throttle the Scan Tool should show a reading of >0.5 V. If it does, a fault in the above systems can be ruled out.






3. Checking For Knocking
Select "READ ON/OFF".
Select "KNOCK CONTR ACTIVE".
Drive the car in a low gear and depress the accelerator abruptly.

If the Scan Tool reads ON, continue with point 4.

If the Scan Tool reads OFF, continue with point 6.

4. Checking The Ignition Discharge Module
Fit another ignition discharge module that is known to be OK.
Repeat the procedure described in point 3.

If the Scan Tool still reads ON, continue with point 5.

If the Scan Tool reads OFF, change the ignition discharge module.

5. Checking The Fuel
If knock control is active it could indicate the use of low-grade fuel.
Fill up with high-octane petrol. Repeat the procedure described in point 3.

If the Scan Tool still reads ON, continue with point 6.

If the Scan Tool reads OFF, the fault has been remedied, low-grade fuel.

6. Checking Performance
Drive the car on test and check whether the fault symptoms persist.

If the symptoms persist, refer to Before Replacing A Control Module.

If the symptoms have gone, the action taken to rectify the fault was correct, otherwise the fault is of intermittent nature.