Thread: Hello and help please...

Hello everyone and thanks for viewing this post...

I have a '98 Grand Prix GTP and have owned it for about a year now... just recently started having a few problems with it.

I was driving and noticed some hesitation at highway speeds and when trying WOT for some passing... then the CEL (check engine light) came on... flashed a few times (knew that may not be such a good thing from prior auto ownership of other manufacturers... just a general rule... I guess)...

Anyways, took it to the shop to get a scan and poss some service...

Here is a list of the codes that came up and what wording came up beside them:

P0301 - Cylinder 1 misfire

P0336 - Crank Position circuit range performance

P0420 - Cat Efficiency threshold

Also, you should know that a couple months ago I noticed some pretty bad misfire/sputtering/loud exhaust issues while driving... took it to the shop to get it diagnosed and as a result got my plugs/wires done... my check engine light came on and even flashed as well as having some pretty badly fouled plugs! I wish I could remember the codes that came off that time, but I can't be exact but I'm pretty sure they were the same P0301, P0336, P0420... my car was cleared of all codes and it seemed to run good/better (the way it did from when I orig bought it). Thought problem was resolved... so carried on being a happy GTP owner...

My car is a stock GTP and when I got my wires/plugs done I was given 3 different options for plugs and I chose the second option (ranking obviously from 1-3... 3 being best; 1 being worst) and my wires were oem replacements.

Now I've done some reading on this site about the specific codes and have come to the idea that it may be a bad cat... my mechanic is thinking the same thing, but I will be sure to get him to see if there is any rattling going on there when he's got it up on the hoist...

One question I have is, is can I just cut the cat off to resolve this issue? Like I said it's a '98 and I'm the owner... I don't want to sell the vehicle, but I don't want to rule that option out later down the road (whenever that may be)...

My mechanic took it for a test-drive today and noticed the same hesitation and thought it sounded like it was being flooded and actually stalled the car and had to wait abit to start and drive again....

I've also read about switching the coils and see if it followed, which I may tell him that this is one thing that has been suggested by fellow owners that have had this/these same issue(s).

Anyways, that is where I stand. My car is at the shop right now, my mechanic has gone for lunch, and I took the codes from him to look up some possible causes and repairs...

If you have anything to suggest, feel free to do so and thanks in advance for any advice.

I would start with a flow test for the cat. That'll back things up and make it run horribly.

No cat ='s a SES light for sure. Look into MIL eliminators if you are going to go catless.

well, i thought i would update everyone on the situation with my car...

after this post i had all my codes cleared and proceeded to have my cat cutout and drove it like that for quite awhile with no problems, except for my check engine light coming back on and staying on (not flashing). i just continued to drive it until recently when my car started to once again 1. lose the tach, 2. tcs light coming on, and then 3. the car would then stall after the vehicle's temp gauge would rise to @ 1/3... then i'd have to wait several minutes for the car to cool down, i guess, before it would restart and drive.

i took my car to the shop and it pulled a code P0336 so i researched the code again, here, and decided to change/replace my crankshaft positioning sensor with a new one.

i also changed the belt to the supercharger (but i don't think that had anything to do with it) because my mechanic said it was in very poor condition and he didn't want to put it back in. btw, this was the crankshaft positioning sensor that was "behind the harmonic balancer" and he needed a "special tool/puller" to remove the harmonic balancer, i believe/or so he told me, so he could get at the faulty sensor...

lastly, i changed my air filter, but that, too, was probably only for general maintenance/upkeep.

my mechanic then said that my car shouldn't pull any codes (CEL's) anymore for this such problem and IT HASN'T/DIDN'T when i drove it home! it ran very strong, too!!!

amazing what a tighter belt, better airflow, and a good circuit (crankshaft positioning sensor) will do for one of these bad boys!!

crossing my fingers that everything works out. thanks for the "search" feature!

if anything should re-occur i will be back to update this post.... hopefully it's the last i'll be adding to this post!!!

Originally Posted by bdawg

1. lose the tach, 2. tcs light coming on, and then 3. the car would then stall after the vehicle's temp gauge would rise to @ 1/3... then i'd have to wait several minutes for the car to cool down, i guess, before it would restart and drive.

Had the exact same problem, it was my Crank position sensor. After replacing it, I did a case relearn and no more issues.