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Car acceleration cut in half, maybe running on fewer cylinders?

1995 Pontiac Grand Prix GTP 6 cylinder 3.4L 100,000m
I’m not sure how to describe this any better, but while driving down a 55mph road my acceleration suddenly crapped out. I could still get it to go, but I had to put the petal to the floor to get there. Engine was a lot quieter, didn’t have the same pep to it at all. No overheating and didn’t notice a change in oil pressure. I’ve got a diagnostic appointment tomorrow but thought maybe I could get some ball park figures before I get there. Any suggestions on what could be wrong would be great! And any ideas of how much those repairs could cost me! Thanks.

Junebug, Your Vehicle Has The OBD1 (Onboard Diagnostic) System And May Hold Some Clues To This Mystery, Especially If The “Check Engine” Light Has Illuminated Or Is Illuminated.

Newer cars have OBD2 and large national chain Auto Parts stores will read codes for free. I don’t know if they can obtain OBD1 or not, but call them and ask.

Otherwise a search online may give you instructions for using a paper clip or piece of wire hooked to the proper terminals of the OBD1 socket to trigger the CEL to blink you out any DTCs (Diagnostic Trouble Codes). I do this on my older Pontiacs.


Just gave it a try with the paper clip and wire, not getting anything back.

Is The “Check Engine” Light On Or Has It Recently Come On ?
Did You Find thorough Instructions For Obtaining The OBD1 Codes And Do It Exactly Right ?
Do You Understand What You Are Observing ?

I’m not trying to be demeaning, but this is a little tricky going from written instructions and then just trying it. If no “check engine” is present then it probably won’t tell you anything anyhow.

I can think of many things that could cause your symptoms. A code or codes would be helpful. If none are available then the car will probably have to be looked at by a trusted professional.

Is the car running smoothly, not shaking or vibrating, albeit weakly ?


Yes, the check engine light is on. I looked up the diagrams for my specific car, it was pretty confusing since there really isn’t much, but I found the A & B port location (diagnostic and ground) and cross referenced instructions through youtube of similar vehicles to mine. Made sure they were connected and the car was on, on, but not running. Nothing started blinking. Fussed with the paper clip and tried the wire, still nothing. I read that in the 3.4L they started putting OBD1.5s in and I’m not sure if that might be part of the problem

It was running fine, if it weren’t for the sudden lack of response in the gas pedal and lack of noise with acceleration, I wouldn’t have noticed anything.

Did You Inquire As To The Ability Of Any Auto Parts Stores To Read Codes On Vehicles Manufactured Prior To OBD2 (pre - 1996, generally) Free Of Charge ?

Running smoothly, I’d say it’s unlikely that it’s running on fewer cylinders than normal.


Open the hood and on the emissions sticker look and see if this is a non-compliant OBDII engine mangement system. GM started phasing in OBDII in late 1994. So 1995 vehicles weren’t exactly OBDI nor OBDII but something in between. If this is a non-compliant OBDII engine mangement system, you can’t pull codes by jumping between the A and B terminals on the ALDL connector.


Just looked under the hood in a place I didn’t think to look because I thought it was more serious…but it’s my throttle cable. Need a new one, after driving it again it busted clean off. Thanks for your help. :slight_smile:

Good Job, Junebug !

I believe that’s a braided cable, so it makes sense that as the cable strands were fraying it was stretching and that was the reduced throttle movement.

I wish I had a nickel for each time I thought I wouldn’t be able to trouble shoot and repair a vehicle, machine, appliance, or something around the house because of electronics, non-serviceable parts, etcetera, only to spend time investigating and seeing an obvious fault.

Thanks for informing us.