Motor blew up today.....need some tuning experts in here.

[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.


Here is a screenshot of when it happened...









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


*will attach some files when I figure out how*

[Fast355]

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.


Here is a screenshot of when it happened...









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


*will attach some files when I figure out how*

I get a small leaner spike from the torque management spark retard, but nothing quite like yours.

[EagleMark]

I was thinking TM too. But can't remember it ever acting this way? Lag, lean then rich?

Can't really think of anything tune related that could do this if VE is dialed in, especially MAP and MAF?

What happens, or happened... if you were running Open Loop?

Bummer on the piston, but I don't think a 15 AFR lean spike during WOT caused it... unless it was some spark knock not being handled properly for a long time? Have you pulled the plugs and looked for specks/fly turds on the plugs?

[mecanicman]

Look at your map signal, and the coresponding drop in cylinder air. Something mechanical was going on, maybe on the cylinder that let go? I added cylinder air in with map and maf and watched them dance with tps reading 100%, looks like an engine issue to me.

[lwrs10]

I was thinking TM too. But can't remember it ever acting this way? Lag, lean then rich?

Can't really think of anything tune related that could do this if VE is dialed in, especially MAP and MAF?

What happens, or happened... if you were running Open Loop?

Bummer on the piston, but I don't think a 15 AFR lean spike during WOT caused it... unless it was some spark knock not being handled properly for a long time? Have you pulled the plugs and looked for specks/fly turds on the plugs?

Torque management is zero'd out in my tune, so not sure on that. I have ran it full open loop and it will still do it. Does not have to be WOT, it will do it anytime it is above 75kpa, and held there at a steady rate for 3 seconds.

I have even jumpered off an injector and hooked a portable oscope up to it in the cab, and the injectors just shut completely off when these lean spikes happen. So i would 100% say it is the computer causing it. Why.....i have no idea. That is why I am here.

Look at your map signal, and the coresponding drop in cylinder air. Something mechanical was going on, maybe on the cylinder that let go? I added cylinder air in with map and maf and watched them dance with tps reading 100%, looks like an engine issue to me.

That was when it shifted into 3rd, so i would expect a slight dip in the MAP reading. I can post screenshots of this happening hundreds of other times not during a shift and the MAP kpa does not move.

[mecanicman]

From looking at the different logs you posted, I can see this stuff in everyone. Your koeo map value is 102kpa. You never hit that going wot, best I believe I saw was 98kpa. Is your air filter to small, or you have silicone elbow you are sucking shut? You have a map sensor "tick" in your steady state cruise with no tps fluctuation. Something was up with the engine. I have included 2 pics from your logs that are not shifts, and show the same thing I described before. Map sensor doing the funky chicken. Your issue is not tune related.

[Fast355]

I was thinking TM too. But can't remember it ever acting this way? Lag, lean then rich?

Can't really think of anything tune related that could do this if VE is dialed in, especially MAP and MAF?

What happens, or happened... if you were running Open Loop?

Bummer on the piston, but I don't think a 15 AFR lean spike during WOT caused it... unless it was some spark knock not being handled properly for a long time? Have you pulled the plugs and looked for specks/fly turds on the plugs?

I was thinking it was the van that had the lean spikes on the upshifts but when I looked at some of the old logs, nothing. Then I opened a few early ones on the Titan and low and behold lean spike city. Its MAF only but the torque management timing retard was driving it lean. I simply added fuel in the cells used during the load transition. Worked like a charm.

On the other hand that dual planed dry intake modified for PFI may have some strange resonance or d u namic causing it to starve some cylinder and overfeed another. Nobody really knows without seeing the OEM marine tune. I know when I had TBI on a performer rpm vortec the air/fuel ratio varied substantially cylinder to cylinder with over 200* EGT differences between cylinders. When the intake was flowed it was discovered that the runners do not flow equally at all. Some port matching and grinding helped somewhat.

In my application the crossram L31 marine intake caused the whole tune to richen up with only a little more AE needed.