2002 Pontiac Grand Prix Transmission Or Catalytic Converter

I have a 2002 Pontiac Grand Prix. Over the last few weeks i have had trouble with the can being jerky while accelerating also i tends to do this more the warmer the car gets ie: runs good in the am but by lunch time it’s acting up. Also i noticed this morning that the trans didn’t seem to be shifting from 3rd to drive please help any advice will help. Thank you. Jerky feelings happen at all ranges but mostly take off from 0-50 i have even felt it with the cruise set at 70mph. The check engine light comes on and then goes off from time to time i had it hooked up once and they told me in showed no code so i just thought it was the gas cap. The engine is a 3800 series 2 also the mileage is around 120,000. Also when the car jerks i would describe it as wanting to just die the tach will drop some then pick right back up when it does this it dose not rev higher though leading me to believe that the transmission is not slipping but like I said earlier it doesn’t seem to be shifting into drive from third. At 60 mph the rpm’s are at 3000 when they were normally at 2000-2300. Thank you very much for your time.

Well, any time the check engine light comes on, there should be a code as current, or in history, even a loose gas cap. That is really the key to diagnosis. Just by you descriptions, sounds like you may have 2 or more things going on. A common problem for the jerky condition is a misfire in 1 or more cylinders. Will need to have the ignition system check- plugs, wires, and also the fuel injectors. Plug
wires and coils are a common area of problems on the 3800. They cause a poor acceleration. All goes back to the check engine light codes. Coil inspecting, pulling trans. dipstick and check for a nice red color and not a dark burnt color/smell are some things you can do yourself. After that, getting the codes that are probably still in memory is the next step.

This sure does sound like a plugged catalytic converter. A plugged converter can act like a transmission problem or a low fuel pressure problem. Either way it means poor acceleration on the 3800. If the check engine light was on then there definitely is a code stored in the computer. If it was a misfire code then this may be the root cause of a failed catalytic converter or the misfire may just be your whole problem. If the check engine light were flashing then that is the sign of a misfire severe enough to cause possible catalytic converter damage. This is the only reason the check engine light would never flash. Get the codes scan again, have the fuel pressure checked, and have the converter checked.

I agree with the guys above that it is most likely the catalytic converter that is bad. But you better find out why it went bad first place. A bad ignition coil for a long period of time causing an engine misfire can burn up a converter. Or maybe you have a fuel injector that is leaking and making this cylinder very rich. Raw fuel going into the converter will burn and melt the insides to a point where it gets plugged up and causes poor acceleration.

Bad spark plugs will cause a misfire and raw gas getting into the catalytic converter causing it to fail on any car. Leaking fuel injector can also cause this problem. The back spark plug and plug wire on the rear head nearest the drivers side is a common cause for misfires on the 3800 V6 engine.

I’ve had poor battery terminal connections cause the tach to go back and forth while the engine seemed to just “drop out”. At the same time as this was happening, the check engine light would come on and go off sporadically. After checking this with the Tech 2 scanner, no codes stored. So it is possible that the SES light could have come on with no codes stored. Possible loose or corroded battery terminal(s) OR underhood fuse box problem (this is a pretty common issue with Grand Prix’s).

I agree that a stored code in the computer, be it current or history, is the key to a correct diagnosis. All the possibilities that were listed are fairly expensive, too expensive to be guessed at in my opinion. What you probably need to do is drive it long enough to get it to start acting up, then drive to a dealer or known, good, dependable shop and have someone who deals with performance issues daily check it out WHILE IT IS HAPPENING…otherwise you will most likely get the old “Sorry, we couldn’t get it to happen”. Ride with them once you have it in failure mode, that way you can say “See, there it is”.