Turbo Diagnosis Tips

Before condemning the turbo, check everything between the turbo and the engine first. A boost leak in the charge air piping — the hoses and pipes between the turbo compressor outlet and the throttle body — is the most common cause of underboost. These plastic or silicone connections crack, slip off, or develop pin holes. A boost leak lets compressed air escape before it reaches the engine. Use a smoke machine in the intake system to find leaks. Also check the wastegate actuator for proper operation — a wastegate that opens too early or stays open limits boost.

A turbo with worn shaft seals leaks oil into either the intake side or exhaust side. Oil on the intake side produces blue smoke on acceleration as the engine burns the oil pulled through the compressor. Oil on the exhaust side produces blue smoke that may be visible at the tailpipe. Before condemning the turbo seals, check the oil drain line from the turbo back to the engine. If this line is restricted or kinked, oil backs up in the turbo bearing housing and forces past the seals even though the seals themselves are fine. Clear the drain first and recheck.

With the intake piping disconnected, reach in and feel the compressor wheel. It should spin freely with no grinding or catching. A small amount of radial play — side to side — is normal. Excessive radial play where the wheel contacts the housing, or any axial play — in and out along the shaft — means the bearings are worn. If the compressor wheel shows any damage to its blades from debris ingestion, the turbo must be replaced and the cause of the debris must be identified and corrected before installing the new unit.