1999 Pontiac Grand Prix Misfire Diagnosis from Computer Cod

Tiny
ARMONDO
  • MEMBER
  • 1999 PONTIAC GRAND PRIX
  • V8
  • 2WD
  • AUTOMATIC
  • 152,000 MILES
My check engine light currently goes off and on. One day while it was on, I went in to an Advanced Auto parts store and borrowed an engine code reader and it said that I have engine misfire. The Auto parts guy said that I need to change the spark plugs and everything should be okay. I should simply buy a service manual and read through it and it is very simple. The symptoms of my car is that I feel an engine vibration when I apply my brakes when driving down the highway. When pressing the accelerator everything is smooth. This usually occurs when I'm slowing down from a faster speed. I also get this vibration when driving at a slow speed at stop signs and red lights. Is this a good diagnosis from what I described?
Friday, May 15th, 2009 AT 6:09 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
A tune up may take care of the problem as far as the vibration, but you have me confused with the vibration when slowing down. The engine isn't under a load at that point and you shouldn't feel anything. Where do you feel the vibration the most shen slowing, in the brake pedal or the seat of the car? I question if that is from warped rotors or drums.
Was this
answer
helpful?
Yes
No
Monday, May 18th, 2009 AT 8:08 AM
Tiny
ARMONDO
  • MEMBER
  • 2 POSTS
I feel the vibration probably under the seat mostly. Sometimes there is a vibration simply when I'm going a little slow. I believe I've changed the brakes recently (6 mos or so).

-Thanks
Armondo
Was this
answer
helpful?
Yes
No
Monday, May 18th, 2009 AT 9:17 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
If you feel it more from the seat, chances are the problem is in the rear. If it only happens when using the brakes, have the rear drums checked to see if they are out of round. Chances are they need cut.

Let me know what you find of if you have other questions.

Joe
Was this
answer
helpful?
Yes
No
Monday, May 18th, 2009 AT 11:25 AM

Please login or register to post a reply.

Related Engine Misfire Content

Intermittent Misfire
VIDEO
Intermittent Misfire
Instructional repair video
Misfire Random Code P0300
GUIDE
Misfire Random Code P0300
The world of automotive diagnostics can be complex, with numerous codes and potential issues to keep track of. One of the more common engine diagnostic codes is P0300, which...
VIEW MORE