Trouble Shooting Sudden Shift of AFR at low RPM

[Farva_84]

Ok, So I've been reading through every old thread I can find and haven't found a solution yet, but I have theory or two. First, the car....
02 Gt Manual-Procharger, C&L Plenum, PP 75mm TB, BBK LT's, ORX, Cobra Injectors, KB BAP, Navigator Fuel Pump. Tuned by LSX Killrs of KC, MO. 423hp/433tq.
The Problem: Literally, overnight starts going lean at tip in. During warm up phase, throttle responds perfect and AFR remains steady. When it goes into closed loop, I start getting lean codes on bank 2 when I give it gas. Wide band AFR is plugged into bank 2 verifies narrow band info/codes. When I push the pedal in just enough to jump the RPMs up to 1500, it responds, stumbles a bit while going lean and then seems to stabilize if I hold the pedal steady. After the initial stumble/lean thing, when I hit the gas, if I hold the pedal steady and let the "stumble" pass(takes 1/4 second) the problem seems to disappear until I let off the gas and try to push it again, then the same thing happens again, every time I hit the pedal.

What I've tried so far: Checked for vacuum leaks, none...checked/tested EVERYTHING that hooks to the intake with Multimeter/vacuum gauge and sprayed brake cleaner everywhere....nothing.
Looked for exhaust leaks, none.
Replaced bank 2 upstream 02 sensor...no change.
Replaced TPS, no change.
Cleaned MAF/air filter, no change.
Replaced Alt/Battery, no change.
STFTs look good.
Fuel Pump Duty Cycle is spot on from previous logs and remains constant.
Injector pressure is even.
Plugs look good.
No misfires detected through forscan.

Last details: This happened once before a few months ago. As soon as I noticed it, i stopped the car, restarted, problem went away. Also, since supercharging/upgrading fuel system, I've had a random spike in voltage to the fuel pump that was strong enough to blow out spark. And I'm new to forscan, but when I hook up forscan, it can't get data on egr, 02 sensors, or evap.

Theories: Loose connection somewhere, might explain the lack of communication with forscan.
Bad or Failing PCM.
Bad or Failing Fuel Pump...duty cycle is consistent but maybe not?

ANY input or ideas/procedures/tests is appreciated.
THANKS!

 

[Bullitt347]

First off, I would like you to explain how a spike in fuel pressure could blow out the spark?
Secondly, it is possible the S/C bypass valve is too sensitive (weak/leaks) Your transition from vacuum to boost (no vacuum) is where the stumble is probably happening.

 

[Farva_84]

For the spike, each time it happened, I logged a huge/instant spike in fuel pump duty cycle that would cause the same spike in injector pressure, which, when it happened, would cause the car to cut out and the wide band would swing super rich. I might be wrong.

 

[Farva_84]

Just to be sure, I’ll vacuum test the bypass valve tomorrow. The vacuum line is directly connected to the plenum and to a dedicated port with sturdy 1/4 hose.

 

[Noobz347]

Random thoughts to add to above:

Coil saturation
Weak PiP

 

[Farva_84]

Random thoughts to add to above:

Coil saturation
Weak PiP

Thanks for the response. PiP would be a distributor issue right?

 

[Farva_84]

Alright, so while going down the p1151/1152 rabbit hole again, I ran across a post giving some smart advice "check the fuses" ...so I did...all of them. Found #1 was blown...no biggie, just the cigarette lighter. I replaced it, turned on the car and suddenly my tuner began logging LTFT again. It hadn't been changing any LTFT's for days while I was logging crap...just set at 1.00 the whole time for both banks. I just assumed this had something to do with me resetting the memory every other day. With the long term fuel trims now working, the lean/stumble on tip in is gone BUT, it's running really lean at initial start of the warm up, something that has NEVER happened before!!! If I still had hair, I'd be ripping out by the handful. At this point, I'm thinking that it's time to send off the pcm for testing.

 

[PSKSAM2]

Sorry, all I can think as I read that.

 

[Farva_84]

Alright, so probably the last post until I find the solution. But here's what's up. Last night, my lean issue at tip in, after warm up, suddenly moved to a lean condition on startup when, at the same time, the LTFT's began changing again after being at a static 1.00 for the last two weeks of trouble shooting. This sudden change happened after I checked all fuses with a multimeter and replaced fuse 1 at the CJB. For this session, after the warm up, everything returned to normal! It ran silky smooth and all troubles in the universe went away. No stumble, no lean, no codes. This morning I started it and it went right back to the original problem of running lean at tip in with a stumble after I hit the pedal. LTFT's are still changing but the problem came back!!! After a few choice words of frustration, I repeated my steps...pulled fuse 1, still good, checked all fuses in the BJB with the multimeter and started the car. LEAN AT IDLE AGAIN, ok...thought this might go like it did the first time and run right after warm up...nope! Fuel trims are swinging ALL over the place from max rich to max lean. Wideband is reading 9.8-16.5. Injector pressure and fuel pump duty cycle are still steady. Considering the erratic behavior of the situation, unless somebody has some insight or ideas, I'm going to pull the PCM and ship it off for testing and/or repair. I'd also like to add that forscan isn't able to complete a full scan and pulled two IC codes :U1262 communication error, which is probably because my odometer has a short and goes out from time to time but comes back when I tap on the cluster...and a C 1284 oil pressure switch. ABS light has been on forever.

Catalyst monitoring: Incomplete
Evaporative system: Incomplete
Oxygen sensor monitoring: Incomplete
Oxygen sensor heater monitoring: Incomplete
EGR system monitoring: Incomplete