mcvicar

Hi, a bit of advise please on this current problem.
Have been experienceing the above for a short while, so have been driving steady. Took the knock sensor off, and it was badly cracked so thought this would solve it. Fitted a known good sensor and the problem still exists. also was getting the CEL on under load before this so have changed the MAF also.

I am seeing levels in the 90's. As seen via PFC controller.
Whats strange to me is that if the car is at idle after starting the level would be on 1-2. If I increase the revs steady, it will go to redline showing a max of 25, which I assume is ok-ish. However, from idle again, if I floor the throttle and lift off even as early as 3000 rpm the it shows knock of around 55, if i do the same and take it to 5000 say it will be in the late 80's into the 90's.

Any ideas would be appreciated

Cheers
Del

Mus

iTrader: (2)

could be fuelling related

Pavlo

cracked piston ring land.

Mrchips

iTrader: (7)

Could be a bad batch of fuel.

Pavlo

no it's not fuel related, no amount of poor fuel will create knock levels that high when revving the car without load. I would be very surprised if there isn't a a mechanical problem.

mcvicar

I understand what your saying but why when the revs are increased gently to redline the knock level stays well within limits. If it were mechanical surely the knock at 4000 rpm for example would be the same getting there slowly or quickly.

Pavlo

A piston ring land will rattle on overrun or very light load, revving the car will increase the load on the loose bit and stop it from making a noise. however under load you will see increase activity. Also look for high, seemingly random knock levels on lift off, probably a split second after the throttle is fully closed.

I suppose if the map were THAT far out and the fuel REALLY bad you might be able to induce light detonation by revving hard without load.

With the powerfc in 1 channel monitor mode, set to knock, monitor with the graph (press next on commander if number showing) and you will see the knock. Very short, high spikes are more likely det related, but a more constant lumpy shape is consistent with a mechanical noise.

I would do a compression test on the engine next.

mcvicar

Ok thanks for the advice will check it out.
Cheers

steviecrump

stop it 60's gangster.

mcvicar

How long before the big bang then fella?

Pavlo

if it is a ring land, the engine will probably run at moderate power for quite some time, certainly enough time for you to arrange a rebuild or engine swap. Compression test or even better a leakdown test will be useful. The trained ear will be able to hear a problem with the ring land.

I suppose it could be a failing bearing, but I would have thought you would have heard it, hence I didn't really consider it.

mcvicar

I heard for the first time a rattle this morning on start up, will do a compression test on it tomorrow hopefully. Just trying to free up some time for an engine build. Was trying to go with a re-linered cdb for a 2.5 forged build but it looks like time is not on my side. Was talking to a member on here and he is running 450 on a standard 2.5 sti and has been for some time with no issues so may go that way.
Cheers
For you help and advise though Pavlo, its appreciated.

Cheers
Del

mcvicar

Looks like you were spot on Pavlo.
No.4 cylinder down to 80 psi
No.1 155
No.2 145
No.3 150

The rattle is becoming more prevelant now aswell. Dropped a touch of oil down No.4 and tested again ind it went up to 160.
Oh well thanks again for the advice, spanners out AGAIN!!!!.
Cheers