3.8 litre engine has a strange rattle sound only under acceleration only when driving.Won't do it if you rev it in neutral and won't do it if you try to brake torque it.Just when driving.Had the injectors cleaned,no change,oil changed no change.No exhaust leaks.Any other ideas it may be?
Transmission also has been replaced,also the catalytic convertor and gaskets have been replaced also and noise is still there.Transmission also has been replaced,also the catalytic convertor and gaskets have been replaced also and noise is still there.
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I'm assuming here that you are familiar with driving turbo engines. What do you mean by 'coming and going'? Are you losing boost as your driving or is it not building pressure as you accelerate? This sounds like it might be a 'boost' leak issue. This could be anything from a loose pipe clamp, a faulty wastegate set up to an actual turbo issue.
Give the turbo set up a basic check. Check all of the pipes and clamps to see if any are loose, split or damaged. A hole or leak in the system can cause pressure loss especially at higher engine speeds.
Is the turbo making any strange noises? Get a helper to rev the engine up to 3000 rpm and hold for 3 or 4 seconds and back to idle. Listen for grinding, hissing and rattling noises. Hissing at a steady engine speed suggests a pressure leak. grinding and rattling suggests a faulty turbo.
I would suggest taking it to a turbo specialist as this sounds like it will need to be tested 'under load'.
If you are doing this with no load on the engine in park or neutral then the engine computers automatic rev limiter is kicking in to prevent free wheel/no load damage to the engine components
Try to rev the engine while at neutral if you get the same vibration to pinpoint if its from the engine or the drive shafts. If the issue occurs at a certain rev it may likely be the variable valve unit. Check if possible if you can get errors from the computer.
I had the same problem! I crawled underneath the car and discovered that a heat shield on the exhaust header pipe was corroded and rattling against the exhaust pipe. (Before the muffler) I removed the portion and clamps and solved the problem. Give it a try.
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