Poor Driveablity

FAULT DIAGNOSIS, POOR DRIVEABLITY

Prior Condition
No diagnostic trouble codes


DIAGNOSTIC PROCEDURE
General fault diagnosis procedures for poor driveablity are difficult to suggest. Some useful hints and advice are given in the following.

1. Checking The Engine Coolant Temperature
Cold-starting and warm-up trouble may be caused by the engine coolant temperature sensor indicating an engine temperature that is too high.
A reference temperature cannot be obtained from the EDU. The Scan Tool reading will have to be judged on the basis of experience.

NOTE: If the Trionic has no reference ground from crimped connection J68 to pin 66, the Trionic system will show a coolant temperature that is about 20°C too high even if the temperature sensor is perfectly OK.





2. Checking The Operation Of The Pressure Sensor
Poor driveablity could also result from the pressure sensor failing to supply the correct voltage throughout the entire pressure range.
Check 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.





3. Checking For Leakage
Check the hose connected to the fuel pressure regulator for leaks.

4. Checking The Electrode Gap
The spark plug electrode gap is extremely important for the proper running of the engine. The correct gap is 1.0 - 1.1 mm.
A gap that is too large causes misfiring at full load.
A gap that is too small causes unsteady idling.

5. Checking The Spark Plug Insulator Base
Check the colour of the insulator base on the spark plugs. If any spark plug is distinctly lighter in colour, this may be because its cylinder has been receiving a fuel/air mixture that is too lean.

If this is the case, carry out flow measurement on the injectors.