Engine Knock Or Something Else

[lilcrash]

Hey everyone. My car has developed a very strange screechy noise high in the revs. I thought it was audible knock but my wife said it's coming from the gearbox, it's a similar noise to when I stripped the gears in my rc car, like a grinding gear noise. Is it possible it's my throw out bearing? My throw out bearing is noisey, has been since I had my clutch replaced. Next thought was valve bounce/ cam lash. Any ideas where to look? Thanks

[KiwiRS4T]

Did you replace the release bearing when you did the clutch? Does the noise change when you depress the clutch pedal?

Other ideas - cam belt or other drive belts - try turning the aircond on and off. Pull the top cambelt cover off and have a look at the belt for damage or misalignment.

Have you had your tune? Shouldn't be doing high revs if you haven't.

[lilcrash]

Yer it's been tuned, yes the noise changes with depressing the clutch. They were supposed to replace the clutch, throw out bearing, front and rear gaskets when the clutch was done. They gave me one of the gaskets back and said it didn't need it. But my gearbox looks like it's losing oil somewhere. It's covered in it. Both at idle and the high rev noise goes away when you change gears as it drops the rpms.

[lilcrash]

The noise sounds to be at the rear of the engine/front of gearbox somewhere but it's hard to pin point as it only happens for half a second before I stop accelerating.

I just went for a drive to see if disconnecting the waste gate/ try running without an air filter fixed my boost issue and something strange happened. 1st run(no waste gate lines) hit 30psi. Bad idea, pull over reconnect. 2nd run(as normal) boost drop off isn't constant only in certain gears/load points. Pull over. 3rd run(no air filter) goes as normal untin 4th gear 165/170km/h, bang, miss miss miss miss miss miss etc... Slow down, pull off highway, drives as if intercooler pipe has come off. Pull over. No pipes off. Nothing unusual. Do uturn, big skid, drive home. Possibly slightly laggy response. Still hitting 20psi no issues.

So confused.

Edited September 25, 2011 by lilcrash

[KiwiRS4T]

If you can't or don't want to do your own work ( I can but I am too tired/old/can't be ...) then it becomes very important to find a mechanic or workshop in whom you can have full confidence and price is a secondary consideration as a cheaper cr*p job just ends up costing you more.

Did the same shop do the clutch and the tune?

Clutch should have included new pressure plate, driven plate, release bearing and spigot bearing and any leaks should have been reported to you.

Who did the tune? Are you happy with the result? Post up the charts!

If you disconnect the hose to the actuator it will free boost til it goes bang!

You can have a major boost leak without the pipes coming off so you need to check all the clamps and if necesary paint with soapy water to look for leaks. Otherwise take it back to the tuners ( maybe ring them first and describe your problem). Do you have the stock inlet manifold? If it has been taken apart (say to fit new injectors) then if the gasket is misaligned and squeezed it will make a horrendous noise. New metal based gasket is better.

Could be leak from turbo mounting gasket

[lilcrash]

i try to do alot of the work myself, i just didnt fancy trying to do the clutch in my garage as i can barely lift a toyota supra box on my chest let alone a massive 4wd stagea box. a 4wd place at nerang did the clutch, since it was done the throw out bearing has been noisey. i bought an excedy heavy duty organic clutch kit and got them to install it, it included a pressure plate,clutch plate and throw out bearing. but didnt include a spigot bearing.

efi performance did the tune, not happy with the result or the tune or their abilities. the dyno sheet is in the hypergear thread. its loosing boost badly, unknown reasons.

thats why i disconneted the wastegate line, to see if it was the wastegate actuator.

im gonna go pull it all apart and see if anything split, i just needed to wait for it to cool down. yes ive got the stock inlet manifold, i pulled it off to do the injectors.

il check the turbo mount bolts while im pulling stuff off.

[KiwiRS4T]

OK I've read the hypergear thread. I hope you've cooled down a bit. Not good to vent online.

Your major problem seems to be lack of boost and apart from a cheap and nasty boost controller which may not be the problem my guess would be as above - the gasket between the top and bottom of the plenum. It is easy to misalign and will result in boost loss including a funny screech at high revs ( I speak from personal experience here). If the gasket is in fact distorted you can buy a metal reinforced one which will hold its shape better and is more likely to stay in the correct position so definitely woth double checking.