E92 Engine problems

[richard_abra]

Hi, We have a BMW M3 E92 engine running Pectel Cosworth management in our GT3 spec race are, it has been mapped on a bench dyno by an operator recommended by Cosworth.

Engine internals are completely standard, and the engine had originally done road miles before we turned it into a race car.

Now data showed bank two getting richer and richer as the race progressed and the ECU tried to compensate by taking out 12% but it was still way to rich. so took the plug out and found this..



compression was down to 120 psi and went up to 190 with a drop of oil, so i took the head off and found this...



so popped the piston out and found this...




Engine is only run on race fuel, and to be honest has over heated a couple times and there are some signs of the piston grabbing the bore, no signs of det, 12.0:1 compression, highest ignition is around 31*,

Any ideas?


Thanks

Edited by richard_abra on Wednesday 4th August 21:57

[richard_abra]

[richard_abra]

[Pumaracing]

Time I started charging. How much you willing to pay?

[richard_abra]

well depends on how much you help!!! i want to say to much ignition BUT why no det?

[TheEnd]

^
He'll know!

Basically, that's detonation. I wonder if the lambdas were round the wrong way?

[richard_abra]

really? caused by what? granted the wear on the bearings show signs of to much ignition, but i cant see anything on the piston or head..

[TheEnd]

Well, PumaRacing guy is the expert, but i always though that when the piston egdes break off like that, to the ring lands, that's from detonation.

It is called a "classic sign" but maybe there are other causes?


edit- just done a quick bit of reading - I'm changing my theory!

What can cause that is the piston overheating, expanding, and then ripping the edge off the side. It's not from detonation, although often seen at the same time. That's why you aren't looking at melted or pitted metal (apart from the chips from the loose fragment)

next up is why it overheated, and why the ecu thought it was rich and leaned it out.

Edited by TheEnd on Wednesday 4th August 22:23

[Pumaracing]

Actually I'm going to reserve judgement until I see better pics. They are too out of focus to identify the damage clearly.

[stevesingo]

I don't think it was caused by over heating.

In this pic, there is no evidence of scuffing on the 2nd ring land.


And in this pic you can see some errosion at the 12 O'Clock position


Almost certainly detonation.

Any sign of a misfire on the other cylinders on the bank? The ECU clearly thought there was a rich condition when there wasn't. Do you have knock control?

Steve

Edited by stevesingo on Thursday 5th August 08:45

Edited by stevesingo on Thursday 5th August 12:14

[Pumaracing]

stevesingo said:

I don't t(h)ink it was caused by over heating.

Almost certainly detonation.

Edited by stevesingo on Thursday 5th August 08:45

Agreed. It's actually pretty much a no-brainer although I do hate relying on out of focus pics. The detonation is clear to see on the top of the piston and around the top land. There's no scuffing below that on the second land or skirt so it's nothing to do with piston expansion or overheating. I'm mystified as to what the OP thinks det looks like if he can't see it.

The reasons are also obvious. 31 degrees of advance on a modern 4v high compression engine is way too much. I'd expect closer to 25 degrees max at full throttle and peak power. 31 degrees is 2V territory.

The ECU symptoms are no harder to deduce. The engine ran into det, the piston turned into Swiss cheese, a piece of piston broke off and bounced around until it had buggered the spark plug electrodes, that cylinder stopped firing and just pumped raw fuel into the manifold, the lambda sensor decided that meant a rich mixture and started cutting fuel which meant the other cylinders ran weak and it's only by the grace of god they didn't then start detonating and blow up too. Probably because the engine was already broken so it didn't matter.

Another one to chalk up to crap dyno operators who charge a small fortune but never give you your money back or pay for the repairs when they break your engine.

Bored now. Going away again. Lol. Someone please post something vaguely taxing.

[stevesingo]

Pumaracing said:

stevesingo said:

I don't t(h)ink it was caused by over heating.

Should I put up another post with typos. Should keep you busy;)