Unstable turbo gauge, varying engine torque when accelerating.
Symptom: Varying engine torque or unstable turbo gauge reading when accelerating.
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Unstable turbo gauge, varying engine torque when accelerating.
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Fault symptoms
Varying engine torque or unstable turbo gauge reading when accelerating.
Conditions
This fault can arise:
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After changing the turbo unit.
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After adjusting the basic charging pressure.
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After changing a blocked catalytic converter.
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After repairing an air leak.
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After changing a defective air pressure valve.
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Diagnostic procedure
Carry out charge air adaptation as follows:
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1.
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Coolant temperature should be over 80°C. Turn off the A/C or ACC.
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2.
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Let the engine idle for 2 minutes. Turn off the engine.
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3.
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Repeat the previous step 3 times.
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Diagnostic help
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1.
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Since the charge air absolute pressure sensor is used to calculate mg air per combustion, it must be checked first of all. Compare its value with the value for the intake absolute pressure sensor. These values should be within 10 kPa. A spread of a few kPa is often found and is acceptable. If the intake absolute pressure sensor value is too low, the engine performance may be reduced to protect the turbo unit from overspeeding.
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2.
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Drive the car in a high gear, preferably up an incline. Do not allow the engine speed and load to increase too rapidly in order to attain reliable values. Compare the readings.
a) Air mass per combustion.
b) Calculated air mass per combustion.
These readings should not differ too much. To determine the difference in percent, use the reading "Air mass per combustion, deviation from calculated value".
This value is delayed slightly, however, as it is calculated in TECH 2. The difference should be equal to or less than 10%. Check for an air leak if the difference is greater, see
Leak check, fuel pressure, flow capacity and adaptation procedures
. Otherwise, go to step 3.
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3.
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Drive the car in a high gear, preferably up an incline. Do not allow the engine speed and load to increase too rapidly in order to attain reliable values. Compare the readings.
a) Max engine torque at current engine speed.
b) Engine torque.
The readings should differ as little as possible. A reduction of up to around 15% of the engine torque is considered normal due to knock control. To determine the difference in percent, use the reading "Engine torque used at actual rpm". This value is slightly delayed since it is calculated in Tech 2. The value should preferably be 100% but 85-100% is considered normal.
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