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Am I Going Crazy?

aphid

By aphid,
in Engines & Forced Induction

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aphid Proficient

aphid

Posted
Posted

Hey guys,

Just a quick call for oppinions on a little something :)

The other night I took the old girl for a spin and tune. She's an r34 GTR with a highmount t04z, 700cc injectors & power fc. I use my laptop to tune with an FC Datalogit & exhaust temp meter just for the moment till I get another wideband to measure the afrs.

Anyway, I was brake boosting along and did have a little bit of a knock, registered at around 60 on the power fc knock meter. I didn't think much of it till later on in the eventing when I was brake boosting again throwing a little more ignition on and I hear a tapping coming from the engine bay.

A quick diagnoses by myself, it felt related to actual cylinder pressure, in that it would really only come on at around 2200rpm before it either dissapeared by 3200 or was drowned out by engine noise, but would seemingly increase in intensity related to boost.

The noise itself was pretty mechanical, it sounded like a VERY noisy rocker, so straight away I thought oh god I've spun a bearing.

Anyway, flash forward to yesterday, I'm half way through pulling the engine out when I decided to call it a night. I returned thismorning to my parents (where I'm pulling it apart) and began work again. I went to detach the exhaust off the back of the turbo (high mount V band t04z) and noticed that it was actually missing two bolts out of the T4 flange where it bolts onto the exhaust manifold....

Now this has me wondering, surely I would've been able to diagnose a f**king exhaust leak, with the amount of play the turbo had it would have been making ridicioulus amounts of noise on idle and struggled to boost at all.. The cynic in me is thinking that somebody has had a go at pulling the turbo off as I just had the car parked behind the house with the bonnet up all night (it's a pretty good area) as there is no way I couldn't have noticed an exhaust leak that big, but there is still a part of me that wonders if I was stupid enough to misdiagnose the problem :D

This definantly souded like a bearing, what is your oppinion?

Thanks for your time :)

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The Dan Grand Master

The Dan

Posted
Posted

Get a 1M long piece of heater or garden hose, put it on top of each spark plug hole while someone with a breaker bar rocks the engine back and forth in various locations of it's rotation. You can usually hear a decent knock through the hose if you are on the faulty cylinder.

My bet would be bearing unless it's exhaust manifold leaking only on one cylinder. Sometimes they can make a loud cracking type noise associated with just that cylinder.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

With the play on the turbo - how is the exhaust itself mounted?

If its very rigid, could be the exhaust was helping to hold the turbo in place.

I've seen setups where the exhaust actually putting stress on the turbo/manifold, from being mounted poorly, has causes cracks in the manifolds and so on when there really shouldnt have been.

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