Mechanics

CAR SHAKING

Pontiac Grand Prix

Just looking for some help. I have a 1994 pontiac grand prix 3.8 v6 with 122,000 miles. My car started shaking about a year ago, it would idle really rough while I was at stop and go lights usually. It got to the point where it finally died, and when I unhooked the spark plug cable from coil, it was black on the metal part the cables attach to. So I replaced cables and it ran perfect for about two weeks. Now, anytime I go over about 45 mph, my car starts to shake back and forth really bad. If I am under that it usually runs perfect still, and while I am idiling it doesn't shake at all anymore. If it is shaking really bad, and I keep the gas pedal at the same spot, it starts to slow down. I have to accelerate for it to speed up, and when the rpm's rise the shaking usually stops for a little bit but comes back right away. Like I said, it only happens once I reach speeds about 45mph. Any ideas?
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Ryanz2006
January 21, 2007.




Do you feel it in the steering wheel?

Does it seem to be more of a misfire or vibration?

The description of your symptom seems more of a wheel balance, or bent rim kind of problem.

I used to feel it in the steering wheel before I replaced the cables but now not so much. Its getting to the point where when I started it after work today, it started shaking right away while I was coasting and while I was coming to a stop. I'm pretty sure it has to do with the engine or transmission versus wheel problem because when it shakes the rpms jump up and down in sync with the shaking. Also, when it was working perfect a couple of weeks ago I was getting 180 miles per half tank. Now i'm down to 140. I had this problem with bad gas mileage before I fixed the cables, then after I fixed them it went up, then the shaking started and now its going down. I'm going crazy thinking everyday my car is going to die on the side of the road. If there is any other imformation I can give to help let me know. Thanks so much.

Tiny
Ryanz2006
Jan 22, 2007.
One thing that may help is getting codes retreived from the computer.

If we do have a misfire going on, The very biggset concern on that motor is a leaking intake manifold. They are plastic and have a weak spot. Has your coolant level dropped at all?

In regards to last post, I just drove car around for a little while and watched the rpm pretty closely. When the car chugs while driving the rpm rarely moves up and down. I must have just thought so because it used to always do that before I changed spark plug cables. One thing I probalby should mention is that for about a year and half my car has been burning oil, I usually need to add 2 quarts every one to two thousand miles. I checked the coolant when I replaced cables and it was where it should be. I tried taking it to autozone where they test for free and they said because of the year of my car they couldn't get the codes from it. Can a mechanic get codes from it or does a 1994 not have that capability with its computer system?

Tiny
Ryanz2006
Jan 22, 2007.
There are code readers available that can be purchased and most shops have the adapters to read the codes. IT isn't as nice as OBDII but it can help. It's tough to assess over the net without driving it. I wonder if the massive oil burning has contaminated the O2 sensors and or the cat?

Yeah I was defianately starting to think it might have something to do with the exhaust. It seems that everytime it chugs the muffler makes a " putt" noise and it gets pretty loud. You think maybe the cat could be the problem? Otherwise if the o2 sensor got contaminated what woudl that make the car do?

Tiny
Ryanz2006
Jan 22, 2007.
Hard to say w/o hearing it, but if the cat is plugging up it will run rough and be hard to get power. The O2 sounds more feasible in that it will affect the air/fuel ratio, leaning it out or richening it up. With the gas milage loss, it may be richening the mixure and accounting for the poor economy. That's why it would be nice to have some codes to work with.

Where can I take it to get the codes read? An auto mechanic or can I take it somewhere else? I will go and get the codes once I know where to take it and let you know what they are.
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Tiny
Ryanz2006
Jan 23, 2007.
You should be able to pick up a code reader at any parts store. It may come in handy in the future.

I'm looking at all these code reader parts and they all say for post 1996 cars. My car is a 1994 without the obd 2. Do you possibly have any list of stores or a online website I could buy it from?

Tiny
Ryanz2006
Jan 23, 2007.

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