Throttle self-closes on dyno at 7100... but why?

[davepl]

We are doing dyno runs on a race-prepped LS7 with a GMPP LS7 controller that should run to about 7300. However, on each pull on the engine dyno the last frame I get is an rpm of 9071, at which point the ecm backs the throttle off, lets it open again, backs it off, and we lift the pedal in the control room to abort the run.

I've set the Extreme limit to 7400 and the limits in each gear to 7400 (for testing, these won't be the final values). Is there yet another spot that I need to find for the rev limiter?

Or is there something else that the engine could be "protecting itself" from? There are a couple (4-6) degrees of knock retard, and AFRs are in the 12.2:1 area.

We are seeing the fuel pump hit its limit; it drops a little below the 57psi of the rest of the run, but doesn't lean it out (or at least not enough to move it above 12.5). I thought maybe the ecm could panic if its seeing the drop in fuel pressure, no idea.

Thanks!
Dave

[davepl]

No ideas? Can't be the first time this has happened to anyone, can it?

Maybe I'll go the other way - has anyone gotten an LS7 to run over 7100 with a factory computer? This is the crate motor ecm, and while I can see that they'd have a conservative limit in the default tune, I should be able to get around it somehow!

[daniel76309]

You probably already know this, but there is a section which I believe is called "fuel cutoff", which is a bit of a misnomer in that you can enable spark or ETC to limit RPM's. It sounds as if your ETC limiter is "enabled" for ~7100 RPM (assuming you didn't actually mean 9071).

[davepl]

You probably already know this, but there is a section which I believe is called "fuel cutoff", which is a bit of a misnomer in that you can enable spark or ETC to limit RPM's. It sounds as if your ETC limiter is "enabled" for ~7100 RPM (assuming you didn't actually mean 9071).

Here's what I set. This is ALL under Fuel -> Cutoff/DCFO

Extreme Cutoff
Cutoff RPM vs Gear (Changed each cell)

So even if I missed the 'Control Method' the limits should all be raised. The only thing I didn't change was the overspeed light.

Is there anywhere else other than that I could have missed? Torque management seems to be off.

[daniel76309]

I don't know of anything else, but I am sort of a beginner at this, so there may well be...

[SultanHassanMasTuning]

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