Stuttering at WOT and stalling issue

[Swordsmith]

For many months now, I have had a pair of annoying problems. They don't prevent me driving the car, but they do interfere with really enjoying it.

One, the car stalls, but only when dropping into idle, only if the compressor is running, and only if it is warm out and the engine is warmed up. I can switch the AC (or defrost) off and go to idle, then immediately switch it back on, no problem. But with all the above conditions met, the car will stall at least 50% of the time.

Two, I get a strong stutter, or even a bucking, if I am at WOT and go over 4K rpm. I can go all the way to 6300 if I go gently (say half or maybe even 3/4ths pedal). I can floor it and go to 4K, shift and repeat all I want. I can even push through the stuttering and get to 6K+ despite the stutters... but it seems really bad and I don't.

I will try to remember all the things we tried last summer working on this, but none of them worked. I had work to do in the fall, and the car was drivable, particularly once I no longer needed AC and didn't yet need defrost, so I let it go until now.

Yesterday I did another round of attempts to fix the issues. I tried:

Swapping in a brand new MAF sensor
Changing the BPV
Putting a stronger spring in the BPV
Replacing the hose fitting on the BPV, which had a pinhole leak
Running a smoke test on the whole intake system, no signs of leak (once we capped the intake tube. Seeing smoke pour out the ZZP intake was funny)

Current plan is to replace the O2 sensor next.

Codes I have seen recently:

P015b
P0172
P2097

All of which point to 02 sensor problems, although I have been told many other problems are seen by the ECU as 02 problems.

I also have a long term fuel trim of -21 or so (it fluctuates but remains negative)

 

[Larrymer]

What are your mods?

Put the stock air box and intake back on and let me know what happens.

 

[Swordsmith]

ZZP intake with the insert removed
Solo Performance exhaust with resonator delete
Bosch 42# injectors
Forge BPV
Buick Regal alcohol sensor
Bypass bypass
VT turbo clipping
VT Tune
Water pump (this is not a mod, but it was replaced around when these problems started)

The car ran fine for over a year on the ZZP intake, I am not sure it will run on the stock airbox anymore, but I don't see any harm in the experiment. I will give it a try today if I find the time. Also will try putting the insert in the ZZP intake, which should bring it closer to the stock air levels.

Looking at my UG last night, it looked like the real problem might be exceeding 12 psi boost. Again something I used to do regularly with no problems, with all the above mods.

 

[Sneakerfix]

Did the issues start before your tune or after? Plugs gapped at .28? Also remember Vtuner doesn't like tuning after market intakes


Send Brian a data log you need tuning since your going rich

 

[Scot]

Log your fuel pressure. The stuttering under full load, yet not while "gently" taking it to redline makes it sound like fuel starvation.

 

[Sneakerfix]

Log your fuel pressure. The stuttering under full load, yet not while "gently" taking it to redline makes it sound like fuel starvation.

But wouldn't he be throwing lean codes and not rich codes?

 

[Hulty]

Swordsmith, pardon me as I'm a little late to the party, but I though you should know that I experienced something VERY similar(couldn't say identical without saddling up in yours) to what you're going through and it turned out to be a faulty coil pack. That being said, the coil pack with a large asterisk behind it. Reason being, it wasn't the electronic part of the pack at all but the rubber boots that slide onto the plug. In my instance there was a minor tear in one of the boots, HOWEVER any degradation in the INTERIOR of the rubber boots can cause an arc to that cylinders spark plug resulting in the spark emitting from the porcelain shaft of the plug rather than the tip. IN MY CASE, if you know what you're looking for (magnified if necessary) evidence can be seen in the form of carbon tracking on the offending plug. Keep in mind that my situation was fortunate that it was able to be seen by the naked eye or I may still be going back and forth with the dealer trying to get it figured out, so I can't scream this loud enough ~IT'S COMPLETELY POSSIBLE FOR THIS TO BE OCCURING MINUS SYMPTOMS VIEWABLE TO THE HUMAN EYE~.

If you think about it, the MNFR plugs are 100K miles plugs, the rubber boot design could've easily been engineered (and/or deemed acceptable) by the MNFR based upon it's need to be removed/replaced 1-3 times MAX throughout the life of the car, now take into account how many times gearheads like us pull the pack?

My apologies should this not be the Golden Ticket that finally gets you into Wonka's factory, but I thought I should share.

 

[Hulty]

Forgot to mention, I had ALL the ST/LT fuel trim issues that you are having due to this as well and they ALL went out the door with a new pack.

 

[kevjam79]

It sounds like spark or fuel.

I would start by assessing all of your grounds, clean the battery terminals and inspect the spark boots.

If you are running E85, pull the injectors and have them cleaned and flow balanced. Pull the fuel pump and check for corrosion or gumming. Do you drive the car daily and keep the tank full, most of the time? Ethanol has the propensity to draw moisture and corrode the system. I highly doubt the Sonic is spec'd with the right components to handle the corrosion of E85. IMO, stop using E85, if you are.

Good luck.


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