Heavy stutter on acceleration (not tuneup)


DocDave001
12-19-2007, 12:56 PM
96 GP 3.1
Just had upper gasket replacement for leak under plenum
Tuneup is good
The more you accelerate the worse it stutters
My son barely made it to work today 30k going up a small hill
No cat converter on system and muffler has holes so no back pressure
When you back off the gas it runs fine but this gets worse the more you drive it. Gets to the point only the slightest pressure on gas pedal before it starts to stutter.
Fuel filter is being replaced today but I dont think thats it.
Crank sensor?
No codes set
Maybe a partially frozen gas line?
Suggestions greatly appreciated. I hate working in the driveway in the cold.
Any sensor values I should check?
This only happens under load and was occuring before the gasket replacement issue but much lighter.
Thanks
Dave

richtazz
12-19-2007, 01:02 PM
Welcome to AF.

I'd suggest doing a compression test. You may have a blown head gasket causing low compression in two or more adjacent cylinders. I'd also check fuel pressure to be sure it's in spec. Both would cause your symptoms.

Prix87
12-19-2007, 03:27 PM
hey man,
Driving a 97 gt myself... had very similar trouble couple months ago with 130k on my car. Ran through similar trouble trying to get it right again... goin up hill or accelerating it would jerk/jerk/jerk until I let of the gas and "re-accelerated"... problem was a bum VACUUM MODULATOR located on the transmission. I believe we have the same transmissions. If you can locate it, disconnect it. If trans fluid pours out, thats more than likely your problem..... besides, a lot cheaper to fix. 20 bucks tops with shipping

DocDave001
12-19-2007, 05:15 PM
Good compression
Not the same trans as the 96 I dont think anyways.
always stutters on acceleration, acts like it drops 2 or 3 cylinders as soon as you give it any gas but idles great with no miss. Also starts up fine in the cold, just dont touch the gas pedal.

A guy told me it could be the crank sensor, especially if its not routed correctly. Says that the movement of the old motor mounts stretches or pulls the crank sensor wires if they are not in the right place. I dunno

Thanks for the replies so far
Dave

BNaylor
12-19-2007, 05:40 PM
Not the same trans as the 96 I dont think anyways.


Prix87 is correct. You both have the same autotransaxle which is the 4T60E, GM RPO Code M13. It changed to the 4T65E (M15/MN3) without the vacuum modulator and PCS control later in the 1998 model year.

All GTP's from '97 and up have the 4T65E-HD, MN7.

DocDave001
12-20-2007, 01:03 PM
Thanks guys
Now theres some info I didnt know about
I'll check out that modulator on the transmission, it's probably the culprit
Not going to happen in the driveway though, -10 here today with about 1 1/2 inches of snow and ice still on the driveway (after the plow)
I'll let you know what happens
Thanks
Dave

DocDave001
01-09-2008, 01:25 PM
Well it wasnt the vacuum module on the transmission. It's still doing the same thing, heavy stutter the more you put your foot into it. Light on the pedal and it runs, to a point anyways, once you get so far down on the pedal, or any power required like going uphill it breaks into it's stutter. How about a crank sensor? It does seem better when it's cold but only a bit
Dave

GPFred
01-09-2008, 01:41 PM
Something you might try, I have a 2000 GP that had similar symptoms, but mine was throwing a code for a low-voltage to the O2 sensor. When I changed out the fuel filter, the situation cleared up. The car has run like a champ since. Just something to consider that maybe its a partially plugged filter.

richtazz
01-09-2008, 02:12 PM
Let's back up a few and review.

You said the tune-up was good. What does this mean, and what brand plugs and wires are installed, and did you change the fuel filter when you tuned it up (if you did)?

Is there a CEL on, and if so, have the codes been pulled and could you post them?

Have you checked fuel pressure at the rail, and if so, what was the reading?

DocDave001
01-10-2008, 09:01 AM
Tuneup is OEM components and the fuel filter was not done, Thats my next item along with a fuel pressure check, unfortunately I have to send it in for the pressure check because I dont have anything capable of doing the pressure check procedure.
This vehicle is an ex taxi with 300,000 + k's but I know the previous owner kept good care of it. The stutter began very lightly about a month ago, it continued to get worse until I needed to have some cooling system work done (upper plenum leak). I was hoping that some form of problem would have been found during the fix but due to miscommunication it was never looked for at the time. Now we're sending it back in for this specific problem. I'll let you guys know what it was when it comes back.
My thinking is it can only be vacuum, electrical or fuel.
Vacuum is within spec, fuel we are not sure but getting checked
Electrical starts at the crank sensor, goes to the module, then to coils, wires and plugs. Because it runs great with no miss or problems at idle, I dont think it could be wires (but I have seen break down under load before) More likely module or crank sensor if it is electrical. Coils tend to work or not.
Oh well we'll see, this whole mess is driving my son nuts. It's his car and he really hates to be walking.
Thanks for your help
Dave

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