dij

Just having a little problem with a noise coming from around the turbo when accelerating in 1st or 2nd.

When a a turbo is is over boosting,is there a noticable difference in the noise that it makes?

My turbo occasionally makes a high pitch screach at 1.1 bar,as if its leeking air from a hose,but it wont do it if I keep the boost under 0.8.

Can a noise similar to this come if the waste gate is not opening enough,or is there an explanation for this.

Just a little worried if this is turbo bearings on there way out and the turbine
is catching the compressor housing,or (hoping) its to do with something else.

Trying to find out exactly what Overbbosting actually is.
Any info on overboosting would be helpfull.

Thanks

ALi-B

iTrader: (1)

Your dumpvalve maybe leaking, or has a weak spring, causing it to open slightly under high boost. Sometimes this can make some wierd and wonderful noises.

dij

Thanks for that Ali B,any suggestion as to how to check if its the dump valve?

Any more suggestions anyone?

Dark Blue Mark

Check none of the turbo heatshields are loose, certain resonant frequencies can cause them to rattle / screech.

MB

dij

Thanks for the reply mark ,but imsure its not a vibrating heat sheild as the noise is directly proportional to the boost/revs.

Sounds like air being blasted from a small hole,a bit like a spider farting realy loud.

Dark Blue Mark

Hmm, does sound a bit like a pin hole leak somewhere... Not the fitting on the boost gauge is it?

I very much doubt if its the turbo catching anything as that would ping the blades off. If you rev it hard using the throttle body, while under the bonnet, you can achieve a good boost pressure. Try that and have a listen.

MB

Turbo_Steve

Easiest way to check dumpvalve is remove it, though I wouldn't run without it for long as you may damage the ole turbo there, sonny jim.

Is it an aftermarket item, or factory one?

dij

Im hoping it is a simple thing like the boost gauge fitting,but dreading a pin hole (might take forever to find it..if I do actually find it) coz Im probably going to have to take hoses and bits of just to check.

Ive heard a fkuked turbo before,and the noise does sound similar (ish) but as you say mark,it would break the blades off and the turbine would stall.

Im not sure I could get the car to boost enough when stationery,but I will try,and running the car without a dv on a my99 would require a plate to be made up to block off the hole on the IC.Oh and its a standard factory dv.

Thanks for the input DBM & TS

Im still hoping someone could explain the symptoms of over boost,even if its irrelevant to my problem.

BTW turbo Steve,I have a legacy TT estate my95 coming from japan (only parts) and a n/a legacy,both with good front ends (supposedly).
I will contact you when the parts arrive (1 month approx),and you still have to take me out in your car when you get a chance.

Dark Blue Mark

You should be able to get a good boost pressure when stationary. Ive had the dump valve letting off at high revs on the drive way.

Yep, you would need to blank it off to run without it, though as Steve says it not a good idea long term as it puts a lot of load on the turbo bearings.

Overboost occurs naturally during winter in most cars, because of the density of the air in cold weather. Boost pressure is generally lower in summer. 1.1 should be fine (0.9 is normal on a standad MY99) If it was that bad, the fuel cut would kick in after a fews ecs of overboost. Is the 1.1 a peak or held figure?

I still reckon a listen under the monnet on the drive way will point you right to the source of the noise.

MB

dij

Thanks again DBM.

Youre probably right,I will try that as soon as I get a chance (probably next year at the rate Im going atm).

Oh and btw,the OB is come in use a few times so thanks for that aswell.

Turbo_Steve

Dij...fraid you've been beaten to it by the mad e-bayers! Have managed to get an entire front end, painted in the right colour, for under £100 including shipping. Sorry mate. As for taking you out.....will do. It's off road for a bit at the moment, but should be back soon (if I can get a decent clutch for non-silly money) so I will have to come down and see you

dij

£100 is a good price (******* excellent actually),the main thing is you got it sorted .

I will hold you to the offer for the ride,and perhaps you could do the KL conversion and bring that back with you at the same time.

BTW,are you still looking for a FMIC?,I didnt get round to checking the one from the supra 90,but will if you still need me to.

Turbo_Steve

Not into FMICs......was after something quite different....

Expect a PM