Enhanced fault diagnosis for turbo
Symptom: Low performance, noise or exhaust leakage
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Enhanced fault diagnosis for turbo
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Background
Analyses have shown that 50% of turbo replacements carried out proved to be unnecessary as tests showed that they were not faulty at all. In many cases the faults depend on other faults such as cracked, restricted or loose hoses.
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Note
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There are cases where the MIL lamp has not illuminated or a diagnostic trouble code was not generated despite a fault in the system. Low turbo pressure can also create soot build-up.
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Fault symptom
Low performance, noise or exhaust leakage
Criteria
All driving situations
Procedure
First check if there are any diagnostic trouble codes. In which case, continue with fault diagnosis in the normal way.
If the car has low performance:
Boost pressure can be checked with Tech2 during acceleration from 1500 rpm and up to full acceleration by comparing requested absolute pressure with actual absolute pressure. The difference must not exceed 20-30 KPa.
If the difference is greater:
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1.
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Open the bonnet and identify any loose, cracked or restricted hoses around the turbo, the charge air cooler or the boost pressure valve.
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2.
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Test pressurise the charge air cooler and the hoses from the turbo outlet to the throttle body with 150 KPa (1.5 bar). Use Pressure gauge 83 93 514 and plug-in kit EN-47656.
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Note
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A sticking EGR valve may cause low boost pressure without generating any diagnostic trouble codes.
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3.
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Connect Pressure gauge 83 95 514 between the boost pressure valve and the turbo's wastegate valve.
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4.
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Start the engine and check that the wastegate rod moves and that a negative pressure of at least - 0.4 bar has been built up.
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5.
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If the negative pressure is not built up, check the vacuum pressure from the vacuum pump by connecting Pressure gauge 8393514 to the pump as illustrated. The negative pressure should be at least - 0.4 bar. If the negative pressure is not correct, replace the vacuum pump
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6.
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If the negative pressure is correct, connect Pressure gauge 8393514 to the output connection on the boost pressure valve. Start the engine and run it at idling speed.
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7.
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Activate the boost pressure valve with Tech2. Increase to 100%. The value should now be 0 bar.
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8.
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Check the wastegate valve by connecting the manual vacuum pump 3014 883 to the wastegate valve and build up a vacuum. Check that there is no leakage and that the wastegate rod is moving.
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If the fault is noise or exhaust leakage
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1.
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Check the front catalytic converter's connection to the turbo with regard to leakage.
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2.
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Pressure test the exhaust system by using a soap and water solution or similar. If soot residue is visible on the connection between turbo and exhaust manifold, remove the catalytic converter and replace the gasket. This connection is extremely sensitive and the catalytic converter must be removed at the rear end in order to guarantee sealing integrity by aligning it with the turbo before the screws are tightened.
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3.
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If the noise remains after replacing the gasket, check the exhaust manifold and check the tightening torque on the cylinder head's screws.
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Note
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A cracked charge air cooler or hose may also create noise that appears to emanate from the turbo.
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