Strange stumble under WOT

[adampecush]

Some background: Had the AEM-equipped car tuned on a dying 60 trim CT upgrade. Boosted to 13 psi no problem, but, as mentioned, the turbo was toast. Fast forward to today. The current turbo setup is a 6065 billet turbo on a tubular manifold, controlled by an AEM gauge boost controller.

With the controller off, the car hits ~7.5 lbs of boost, and pulls fairly cleanly (detected a very quick, slight stutter once or twice) though my AFRs are in the mid to high 12s (yes, I'll be dialing those back to mid-11s). With the controller on, the car hit ~9 but stumbled really bad (could hear the wastegate open, close, open, etc). AFRs were again mid to high 12s.

My question is, is this a case of a lean stumble or spark blowout? I'm doubting lean stumble as the AFRs are not excessively high, but am I going to blow out the spark at 9 psi? Granted, this 9 psi is likely equivalent to 15 on the little CT upgrade, but still. Ignition system consists of a DH-61 igniter and is300 coils. Spark plugs are Denso Iridium Power, stock heat range. I checked the gaps and they ranged from .032 to .037. I gapped them all down to 0.029.

Anybody have any input?

I suppose my plan of attack should include the following:
Get the AFRs where they should be
Gap plugs down even further
Change plugs to lower heat range and copper or platinum
??

Thanks in advance.

 

[Van]

So this is a new condition which didn't occur before the new turbo? Has anything else been changed on the car? Can you pull any codes? Van

 

[hvyman]

ngk 4644 copers id start the gap at something like .28.

 

[adampecush]

So this is a new condition which didn't occur before the new turbo? Has anything else been changed on the car? Can you pull any codes? Van

Yep, brand new condition. Nothing else has been changed other than what was necessary for the turbo install (manifold, wastegate, intake pipe, etc). Can't pull codes since I'm on the AEM. I will do some logging though. I had a thought that I might also be experiencing some aggressive timing pull since my a/f ratio is so lean. Logging will confirm that though.

 

[Van]

Yep, brand new condition. Nothing else has been changed other than what was necessary for the turbo install (manifold, wastegate, intake pipe, etc). Can't pull codes since I'm on the AEM. I will do some logging though. I had a thought that I might also be experiencing some aggressive timing pull since my a/f ratio is so lean. Logging will confirm that though.

Well, I'm at a loss to say where to look next... It is a good idea to get all known issues sorted to rule them out. I agree with you there.
In my experience, the 7M's WOT stumble turned out to be oil in the CPS; R&R'd it and problem solved. I hope your current problem gets similarly resolved.
I'm interested in going standalone, and AEM is one brand for the 7M that I'm considering, so I'm subscribed to this thread. Van

 

[adampecush]

I suppose the one thing I did do was remove and re-install the CPS. It was sitting with the gear up so there is a chance oil could have leaked into the body. I'll check on this...

 

[Nick M]

If you are overly lean, your spark could blow out. In other words, cause and effect. Rich is easier to light, in addition to being safer.

 

[adampecush]

Well, I've added around 10% to the boost comp graph, so I'll go for a drive in a bit and see where I am.

 

[supraguy@aol]

Wellll??
This must be a long test drive that you're on...

 

[adampecush]

unfortunately, work is preventing a test drive. and by work, I mean golf tournament.

edit: did some low boost runs where afrs hovered around 12. nothing strange happening, and nothing funky in the logs. added some additional fuel to the map and we'll see what that does at higher boost tomorrow. placebo effect warning: the car felt faster and smoother with the lower afr...

 

[adampecush]

Steepened the boost comp curve a bit more, and am now hitting 11.5-11.7 in the lower RPM range. Higher rpm is still around 12.3 so I need to do some messing with the fuel map. I haven't upped the boost yet since I want to sort out the AFR first. It is pulling a lot harder now with the lower AFR. At 7 psi, the tires don't have a chance in 1st gear. I'm a bit scared to go to 15...

It also looks like I may now be a catch can candidate...angled down intake tube = PCV oil running towards the filter.

 

[Nick M]

Are you supplying a large enough volume of fuel?

 

[adampecush]

I'd imagine I've got enough pump (walbro fwiw), since I had no problems dropping fuel pressure at boost levels up to 15 psi previously. Injector duty at max RPM is only around 40% so I've got a lot of room to play with.

I do have a fuel pressure sensor that I need to wire in to the AEM and FPR...thats probably not going to happen for a while though.

 

[Nick M]

I'd imagine I've got enough pump (walbro fwiw),

That is good. Ever do a voltage drop test on your 20 year old wiring at the pump? I am just offering up possibilities, and not taking the AEM into account.

 

[adampecush]

Already have a relay-driven 10 AWG line to the pump. All body ground points are also tied together with 10 AWG lines as well.

 

[adampecush]

OK, after doing some more reading about the AEM Gauge boost controller, it appears as though I may be an idiot and set up the boost controller wrong. I interpreted waste gate crack pressure to be the total pressure of the WG spring. Apparently setting the SPR function too high (turns out it is higher than my maximum boost) will cause all sorts of fluctuation issues. I'm going to dial it back a lot and go from there.

I logged data for a while and found that there was zero AFR fluctuation during the stuttering (and no timing pulled), hence I'm still getting spark and not experiencing any knock. Roads are wet right now, so no further testing for me tonight. We'll see if the SPR setting was the problem soon enough.

 

[IJ.]

What rpm is it happening at Adam?

 

[toyotanos]

Adam, I like to set my SPR setting about 4-5 psi below what my target boost is so I get the better spool, but not any of the oscillations (or less than there could be)

 

[adampecush]

What rpm is it happening at Adam?

Over 4000 rpm (or during the time when the wastegate would be trying to control boost), pretty much all the way to redline. On one particular log, the AFR stayed between 11.5-11.6 the entire time the hesitation was happening.

On the wastegate alone (~1.5 psi less than the above condition), there was zero hesitation.

All I have to do now is go give it a try...

 

[toyotanos]

Hmm, sounds a lot like when was blowing out the spark last weekend. On wastegate (18psi) it was fine, but when I tried to bump it up to 24/25 it would sputter and backfire and break up badly. Gapped the pulgs down to .023 from the .44 they were at and BAM! no more misfire! I am also running the IS300 coils and DH61 ignitor, if it matters.