Falls on Face at WOT

[Pedal-Force]

So, to make a long story somewhat short, I had tuned the car a few years ago, got it pretty much where I wanted it, as long as I got the good gas it was fine. Moved a year or so after, lost my AP and cable. At some point, I don't remember when, the car started being unable to go WOT. Too much boost and it just falls on its face and starts stumbling, hard. I didn't know if it was knocking, but I suspected it was. Finally found my AP a few weeks back, sourced a cable locally (after much searching for a V2b cable, and an incredible $45 for a small piece of cable with two normal, dumb connectors on it).

Below are a couple datalogs I took yesterday. They're short because I don't dare go WOT very long with it like this, I'm worried I'm gonna vent the block. Mods are in sig, still accurate.

Looks like I'm losing fuel pressure maybe? Is that the first thing that happens, and then the AFR goes lean and then it knocks? The AFR continues to swing wildly from lean to rich and back, and even after I'm off the throttle it's still dumping tons of fuel in.

The second log (datalog3) doesn't have the KR, but you can see that the rpm isn't going up, it's bouncing around, and the fuel pressure still looks low, but it doesn't go quite as lean.

This was with my tune on, but the other day even with stock tune I had the same symptoms. Get into the boost and it starts to stutter and surge. If I had to describe it best, it's like hitting the rev limiter, but slower.

Idle with my tune is fine, but it's also up around 1000 rpm. The stock tune idle seems to hunt and stumble some, but that might be the way it is with my mods. At part throttle the car seems to drive just fine.

Any help would be greatly appreciated. I can do more logs tomorrow with different parameters if that would help.

[MSMS3]

Let’s begin with the simple. The stumble, cut, occurs at high load, high boost, but about 3,500 rpm. Fuel pressure is fine up to then.

Might you be getting boost spark blow out? This happens when plug gap gets too wide over time. Before doing anything else, pull the plugs and check the gap. You want it to be .024” to .026”, no wider than .028”. They will start causing boost blow out (high boost actually blowing out the spark) if the gap gets to .032” or greater.

It’s easy to check and the solution might be that simple. Even if it doesn’t solve your problem, you can check that off your troubleshooting list.

[Jeff23spl]

To me it is looking like reaching a programmed limit like exactly around 2.00 load ???
Is your absolute fuel cut load limit set around this ?

Check overboost fuel cut too

Can you print the tune ?

Does it cut like if you turn off the car for 2 sec and put it back on ?(Programmed cut) or it is like riding on a very bumpy gravel road (usually missfire)

Then have you played around the EBCS to break a plastic nipple or have a cracked hose ? Or can it can be just your wastegate duty that are too high in that area for the limits programmed ....?
A quick check is to disconnect the electric connection at the EBCS to fall into spring boost mode (like having 0 wastegate duty) is boost still easily rise high and easy...there is something wrong around the EBCS. If boost drop a lot, it is your tune that ask too much for the limits programmed...

You should add the injector duty into your log sheme

i made a quick check but i don't see where the fuel pressure would be low, it goes with the load applied to the engine and when load is reduced, fuel pressure is programmed to drop accordingly and this isnM't a problem....But where you are WOT, the pressure seem to remain above 1600-1650 ???

[Pedal-Force]

Thanks for the replies.

I'll check the plug gaps, probably been in there a while now (80k+ miles?).

It cuts more like a programmed cut I think, and I don't get a CEL.

I'm not sure if I can check the tune or not, I'll try. I have the older version of AccessTuner, and it never got moved to my newer computer, so I'll have to dig out the old computer and hope it still works. I don't think I can tune on my newer computer since they changed things. Sucks, considering the money I spent, but it has been like 8 years so I guess I can't be too upset.

I really doubt it's a 2.00 load or something though, because this tune used to be just fine and pulled hard to red line, so I don't think it can be the tune, I think it has to be mechanical, like a leak, or something broken.

[Vansquish]

Sounds like you have a mechanical issue. I'd check all the silicone lines, boost tubes, and the like for cracks and/or splits. Replacing spark plugs with properly gapped (0.024" - 0.027") wouldn't be a bad plan either.

[Pedal-Force]

Went ahead and ordered some new plugs. It's been almost 7 years and probably 60k+ miles, so it's probably time. It's worth it once I go to the trouble of taking the IC off and stuff to just replace them at this point, less than $50 and it's done.

[Jeff23spl]

take compression in the meantime, i don,t think is related but isn,t long and keep engine problems out of the equation

[MSMS3]

Originally Posted by Pedal-Force Went ahead and ordered some new plugs. It's been almost 7 years and probably 60k+ miles, so it's probably time. It's worth it once I go to the trouble of taking the IC off and stuff to just replace them at this point, less than $50 and it's done.

I don't know if that will solve your problem, but your symptoms are consistent with boost spark blow out (and other things as well, though). If you got all those years and 60,000 miles on the car and still running the original set of plugs, those plugs need to be replaced no matter what.

I was never able to get more than about 15,000 miles per set on my MS3. When you raise boost above stock levels, it's just hard on plugs.

Taking the IC off to change the plugs will also give you a chance to inspect the boost tubes, clamps, and the hose to the bypass valve. Something might show up there. It would also be a good time to replace the smaller vacuum lines, like the one on the bypass valve and the lines to and from the electronic boost control. You can buy that stuff by the foot at any auto parts store, dirt cheap. Over time, those lines get hard, brittle, and develop cracks, some of which are almost too tiny to see.

And Jeff is right: The perfect time to check compression is when you are changing plugs and all four plugs are out. Even if all is well, you will have some new baseline numbers for future reference.

I am having some difficulty seeing it as a boost leak, though, since you are building good boost, up to 17 psi right before the car stumbles. I'm no expert on such things, but I would think that if there was a boost leak, it would not have been able to so easily build boost. But, that's not the strong point (if I have one) in my turbo knowledge base.

Good luck. Keep us in the loop.

[Jeff23spl]

i'm not sure either but at mid rpm it can easily overboost above 22psi if the wg fail so it may have room for small leaks but there would be other symptoms....MAf would read high and get a steady rich afr or it won't run good at idle with a leak pre-maf

[Pedal-Force]

Well done guys. It was the plugs. Forgot to do the compression test and didn't have a ton of time before the kids woke up anyway.

Worst plug was driver's side, it was over .045. They were all trash though. Pulls hard all the way now.

Thanks.