Thread: Engine stuttering on hard acceleration

Hello everyone. I just joined GPF and I already have a problem. I have a 1998 Grand Prix GTP. Just recently, I noticed that on hard acceleration, my car will stutter, almost as if it's misfiring, and accelerate rather sluggishly. It makes a kind of bubbling sound/feeling. That's the best way I can describe it. When I do a nice smooth acceleration, there is no problem at all. I gapped and changed all of the spark plugs recently. I am trying to figure out if it is possibly an ignition coil, a bum spark plug, or possibly a fuel injector. Does anyone know a way to tell if it is any of these? I don't think it could be a spark plug seeing how the problem does not happen all the time, only on hard acceleration. If anyone knows anything, please let me know. Thank you so much.

Most people run autolite 104's at your level and gap to .054

Do you scan your car for knock? It looks like you have a HAI.

I just recently found that i am having the same problemm

Originally Posted by zeppelinrocks18

Hello everyone. I just joined GPF and I already have a problem. I have a 1998 Grand Prix GTP. Just recently, I noticed that on hard acceleration, my car will stutter, almost as if it's misfiring, and accelerate rather sluggishly. It makes a kind of bubbling sound/feeling. That's the best way I can describe it. When I do a nice smooth acceleration, there is no problem at all. I gapped and changed all of the spark plugs recently. I am trying to figure out if it is possibly an ignition coil, a bum spark plug, or possibly a fuel injector. Does anyone know a way to tell if it is any of these? I don't think it could be a spark plug seeing how the problem does not happen all the time, only on hard acceleration. If anyone knows anything, please let me know. Thank you so much.

What did you gap them at? Too large of a gap can cause spark blowout during hard acceleration, and would explain why your car is stuttering up top. I would check the plugs regardless of what they were gapped at though, cause it may turn out to be a cracked plug or something.

sounds like the same thing to me.Go hard and the car felt like it missed fired.But all of that lead up to the job I am doing now. I still hope that I do not have to get to the heads.Have all the intake off now and wondering if I should rip off more.

I just talked to a friend that's a mechanic and he said that it could possibly be a clogged catalytic converter. He said it acts kind of like a rev limiter on the car and makes that bubbly feeling/sound. I also found out W-Body's are common for cat's clogging up. I am going to check that first and see.

Is it throwing any codes?
If it is check on here to see what it is:
OBD-2 V6 FWD Diagnostic Troube Codes

Or go to an autoparts store to get it scaned.
Let us know if you find the problem.

Wouldn't checking the plugs be easier? Lots of people crack their plugs while installing them.

It isn't throwing any codes. So it's not the O2 sensor. I am going to check the plugs first and then see if anything is cracked.

Hey again. I am still having the problem with my car although there now is a sound coming from my exhaust when I accelerate that sounds like change in a coffee can, making me think the honeycomb in the cat came lose. I checked the plugs and they are fine. I assumed they were too because during a slow acceleration up to the high RPMs, there was no stutter. There would be the stutter under heavy load no matter the speed of acceleration or just all the time if it was the plugs. What I am curious about is with OBD-2, which cat can I buy? Magnaflow has converters that are universal and around 67 bucks but they state they are OBD-2 compliant. I'm looking at the part number, 99306HM, and I am curious as to whether I can buy that and just have it welded it. That would be awesome and save me some money. Let me know what you all think.

On Magnaflow's website, they show this converter as being the correct one, and I called them and said their universal converters are all OBDII Compliant.
http://www.car-sound.com/02product/d...versal=99306HM

I have changed out the plugs with AC Delco Iridium plugs, and new lifetime warranty 8mm plug wires. I also removed all three coil packs and had them checked out. All three are in good shape. I get a code that comes up "exhaust inefficiency". So now, with the blower belt removed, there is less air going thru the exhaust and the shudder has gone away. Has anyone replaced their cat converter and resolved the shutter?

The code that pulls up is number 0420 "catalyst system low efficiency". The local parts store doesn't know what this means. Anyone know?

Originally Posted by Smokin2000gtp

What did you gap them at? Too large of a gap can cause spark blowout during hard acceleration, and would explain why your car is stuttering up top.

HUH

I had to look it up, never heard of it.

http://www.superchargersonline.com/content.asp?ID=11

when i changed my plugs and wires i had the same exact problem ..it would drive perfect until i got on it and then my car would barely go and a bad sound would come from the exhaust in the back........ i had a bad # 3 plug.....i bought a new spark plug and put it in and everything was fine after that ..so maybe check all the plugs with a new one.....

Well i was having the same problem, but went and just bought a bunch of stuff i planned on buying anyways lol
Reprogrammed PCM
MSD Wiring/ Coils
Magnaflow Exhaust (cat-converter)



but from a local mechanic he specifically said check plugs and wires

Originally Posted by Blown97

HUH

I had to look it up, never heard of it.

SuperchargersOnline.com :: The Skinny on Spark Plugs

Ya I had to learn the hard way what spark blowout was lol.

Like I said, new plugs and wires - plugs gapped properly. Has anyone replaced the cat converter and found this to be the real problem?

X2 First do new plugs gapped properly, if that doesn't help replace the wires. It's unlikely for the cat to cause symptoms like this but it's not unheard of. If you think your cat is the problem you could scan the car to see if you are boost stacking from the clogged cat.

Oh didn't see that you were throwing that code. It's definitely a plugged up cat then. Get it either replaced, deleted, or gutted and your good to go.