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Q: Turbo issues with boost

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My turbo diesel 80 sometimes hit peak boost of 10 psi, which is what i want, but then I can waver or drop to 9 psi with increased throttle. When this occurs there is a faint hiss or psssht of air coming from what i guess is the turbo. Sometimes it even fluctuates between 9-10 psi kind of bouncing making that hissing noise. Could you please give me some idea of what might be happening in the turbo and what needs to be done to fix it?
My car has a manual transmission.

Hi thanks for writing in. The Land Cruiser turbo diesel from that era uses a mechanical waste gate to bypass the exhaust around the turbine when the boost pressure reaches maximum. It should be a quiet and smooth action. It’s possible that you might have an air leak in the intake tract that is allowing the pressure to leak off when it reaches maximum, about the same time the waste gate is opening. The pressure would then drop off suddenly, then the waste gate would close, the pressure shoots back up and the whole cycle happens again. I recommend checking all the clamps and seals on the air intake hoses and particularly the line that goes to the waste gate actuator itself. I’d have a local expert inspect the noise to give you a more precise diagnosis in person. From there, they can move forward with the appropriate repairs.

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