Well....this lean spike issue blew my motor up today.

[lwrs10]

I have been fighting this weird lean spike issue I have any time my MAP reads above 75KPA. It happens open loop or closed loop, speed density or mass air, every single time it passes the 75KPA point and is held there for longer than 3 seconds. It can be seen with my wideband, and the truck stumbles for a second. It is always followed my a very rich spike. It only happens when it is a steady load, never during a transient. I have a fuel pressure gauge in the truck, and it is always steady during the spikes.

I had the truck on the dyno already, and all I did was roll into the throttle so the lean spike happened before I went WOT. It only happens once everytime you pass the 75KPA mark.

I was finally satisfied with my VE table today, so it took it out of speed density and changed it to MAF only. I added a ton of fuel on the top of the MAF table just to be sure it was not lean. Well I didnt shoot that far off, because the AFR came in pretty much 11.3 stable. Little rich, but something I could work with. But I discovered this lean spike still happens WOT, about 3 seconds after flooring it.

I gave it a few short WOT burst just to make sure my AFR was safe before I slowed down and nailed it.

The lean spike happened to show up right as it shifted into 3rd just a tad over 5 grand....a spike of about 15AFR. Well it popped a piston right there. you can see this happen right about frame 6534. As it shifted, you can see the rpms started to rise, then they slowly started to drop even though I was still WOT. Thats where it started to run on only 7 cylinders.

Other spots this lean spike shows up are frames:

517
565
and 4506, with was one of the short WOT runs. You can see it go from 11.3 to 12.5 even though the MAF stayed at 8750hz.




What in the hell is going on here? Please help me figure this out before I blow up another motor....

[turbo 6l]

can you tell me what mod have been done to this motor

[Bill@HPTuners]

looks like an engine swap application to me.

[lwrs10]

Its a Vortec 5.7 stuffed in a 2002 GMC Sonoma, ran with an 0411 computer.

Has LS3 injectors, a small cam, a marine intake, and that's about it.

[Dantheman167]

I don't know much, but it looks like the spike is during a wot shift. maybe your hitting fuel cut

[robstah]

How small of a cam?

I find it hard to believe that a single lean spike (which could also be a misfire, which could be either too little or too much fuel) is going to take a piston out like that. Are you sure you didn't break a valve spring? That would kill a cylinder quickly.