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1.6TDCi - Hiss/rattle noise under acceleration on motorway


geraintthomas
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Hi everyone,

Focus Mk3 1.6TDCi with 151,000 on the clock (belt replaced at 117,000). On the motorway under acceleration, I can faintly hear what could only be described as injector/turbo noise. It's almost like noisy tappets, pinking, or piston slap (I'll try to get a recording soon but road noise may drown it). The noise doesn't increase/decrease with revs, happens at mid-rage revs or higher, and only under load. It won't happen when free revving the car, and if I lift off on the motorway, it disappears. The noise is almost always the same pitch (imagine a turbo hiss when you accelerate, but that hiss has a slight rattle - that's what it's like). It's kind of like a fast tapping/hissing/rattle (helpful I know). Essentially it only happens when the engine is under load and at a constant pitch, which could narrow it down to fuel injection or turbo, with the turbo spooling under acceleration, or the fuel being injected with the throttle.

I thought it may have been a tear in a pipe causing some noise to escape, but I've checked all of the pipes. I've also checked the turbo for any play in the impeller, and whilst there's a tiny bit of radial play (acceptable), there's no axial play, so the turbo seems fine too. The impeller doesn't spin freely mind, you have to push it with your finger for it to turn (you can't spin it).

Then I thought it could be the injector seals. The last diesel I had at high miles had leaking injector seals which resulted in black goo and carbon build up around the injectors. The seals are cheap, but the job is quite a pain to do and it's something I wasn't looking forward to doing. With 151,000 on the clock, it's almost certain that mine would need replacing soon. However, I stripped the top of the engine cover and removed all of the gubbins to take a look at them... they're perfect. I don't know how with this many miles, but the head is squeaky clean around the injectors. It's just clean metal. They also look relatively new, so I'm wondering if they've been changed before I purchased the car. It's a load off my mind knowing they're fine.

So the injector seals are fine, the turbo doesn't seem to have any play (though it's a tad stiff, but I've got nothing to compare it to), the noise is only noticeable on the motorway under load, it doesn't change pitch with the RPM, and sounds like a rattly hiss. I'm wondering if it's in fact the turbo, or if I just need to perform an oil change with some decent oil...

Any ideas? Apologies for being vague!

EDIT: may be worth mentioning, there's a little bit of oil in the turbo/air intake pipe.

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