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Harsh shuttering under hard acceleration in higher RPMs

machinegunsquid

machinegunsquid

New member
So the GTP has developed a nice problem.

Before we get into the problems, the background is

2002 GTP -75k miles.
Speed daddy headers, no cat, no rear O2
Homemade CAI

Rear o2 is just disconnected. No emulator, PCM isnt tuned yet. Popping the P0140 (no rear o2 sensor activity....I wonder why...)

Engine was pulled out 2 weeks ago, and reinstalled. No issues until a few days ago.

About a week ago, at low speed, the engine started to surge. As the car shifts from 2nd to 1st at very low speed, the engine wants to rev up, and the car wants to accelerate. This happens randomly. Giving it gas doesn't help. It will only go away on its own, randomly. Sometimes it lasts for just a blip, sometimes it'll last the entire time Im stopped. If I put it in neutral, it will rev to around 3k and hold steady.
I can hear the intake get louder when the car does this, like the butterfly isn't seating.

Now this wasn't a big issue, as it only affected very low speed operations about 20% of the time. Drivability wasn't affected.

Last night, merging onto I-95 to go to school I was around 75-80% throttle in 2nd, and the car started to buck/stutter hard. Almost like a misfire, but a little rougher. As soon as I let off, it went away. Once I was on I-95, I tried giving it gas again in 2nd. Didn't do it again until I went WOT. This time, around 5k rpm, it was even harsher. Felt almost identical to bouncing off the top speed limiter. Pulling strong, then dead on it's face for half a moment, then strong again.

It also randomly will rev from 2100 to 2400rpm while cruising. Again, this just started recently.

As long as I drive the car normally, there arent any issues. Only under hard acceleration, and at super low speed downshifting into first.


I've check the lines for a vacuum leak, and sprayed all the joints, without any change.

Not sure about the revving at idle, except for a dirty IAC/TPS, or lots of build up on the butterfly.

The random surge is far and inbetween.

After the harsh stuttering, the car popped a P01133 (oxygen sensor circuit slow response, upstream sensor)
I erased the code, car still stuttered, and the code hasn't returned.


I'm hoping it's all related, and not an issue with the trans (torque converter lockup)

I'll be heading home tomorrow to work on the car, as I have almost no tools here at my apt. (was going to swap blowers to my ported GenIII, and my other Stock TB(painted to match)
 


Also, no misfires were detected, and it tossed only those 2 codes.

Trans fluid is full, and clean. No grit, doesn't look, feel, or smell burnt.
 
Took the car out for a spin today. No more codes besides the rear o2 no activity. Still stuttering like a ***** under hard throttle though.
 
Can't read lol. You have an aeroforce don't you? Anything look out of the ordinary? Sounds like my buddies gt used to do he ignored it.
 




Welp...did some poking and prodding.

After many months of detective work (a beer in hand, and a flashlight in the other) I found a possible culprit.

The coolant temp sensor is broken where the brass meets the plastic for the connector. I can wiggle it and reseat it, but it will just slide back out. Hooked up the scangauge again, and lo and behold, popped a code for the temp sensor.


Setup a page with fuel trims, ign. advance, coolant temp, throttle position, etc. Once the car hits 65-75% throttle, the coolant temp drops drastically from 195-180* to -35*...yes, negative 35*.

That's the same time the engine starts to stutter like hell.
When I slowed down to a crawl, the engine did the whole 'lets try and rev up a bunch' The coolant temp was still reading -38*. As soon the car began to idle correctly again, the coolant temp went back up to 185*


So, to my limited knowledge, when the PCM sees that the engine is cold, roughly -38*, the PCM commands more fuel to enrichen the AFR to aid in warming the engine to operating temperature. Which, when the car is already at 5k rpm and spraying fuel, the extra fuel would cause a pretty nasty bog, and possibly no combustion due to an overly wet cylinder environment.

I already have the sensor ordered. Should be able to install it this week.


So, thoughts anyone?
 
any more ideas anyone? Car revs fine and freely in neutral. STFT stays at 0 during hard accel.

No other codes either.

Replaced the supercharger tensioner and belt thinking that it might be slipping like crazy, but didn't do anything, other than fix the nasty squeak.
 
dont have a zzp pcm do you? bc they have in their ignition table, at -20* it advances timing to 20*
 


Nope, stock PCM. Replaced the plugs and wires, and that helped the problem a bit. Still harsh stuttering tho. Replaced the coolant temp sensor and bam! Problem solved
 
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