Need help, but no one ever has an answer

Ok, so i have a 99 GP GT, i love the thing to death.

Got it with valve cover leak, fixed it

And lately when i start it sometimes the car will shake...

Or when its warm out, around 40 or higher and the car is at operating temperatures the car will shake at a stop sign

Also sometimes when i'm hard on the throttle it will surge or feel a lack of power

I've asked around FOREVER and never got an answer...its like no one knows what it is doing

I've even taken it to 3 shops and they tell me they cant get it to do it.

And once I had an SES saying #3 Cylinder misfire, well the coil was new, new wires and plug was fine, so i replace the injector....

What should I do? Suggestions?

Thanks

And lately when i start it sometimes the car will shake...Broken motor mount?

Just a guess though.

Take Care,

Do you see the engine physically moving or is it a misfire condition causing the shaking?

Are you stock or moded? If modded what are the mods? What is the mileage?

What brand/heat range spark plug and ignition wires did you put in?

How about the CAT convertor? Is it the original?

I have 111,000 on the motor. Only mod so far is a homemade ram air system which i'm switching to a FWI when it gets warm.

My plugs are AcDelco Iridiums, just what came in the car. I have Autolite Pro Series wires (i'm doubting those)

And As far as I know the cat is completly original. I'm hearing a little louder noise from the exhaust as of late, i think the mufflers are going on me

And as for seein the engine move, when i've looked I cant tell its really moving unless i place my hand on it

I have 111,000 on the motor. Only mod so far is a homemade ram air system which i'm switching to a FWI when it gets warm.

My plugs are AcDelco Iridiums, just what came in the car. I have Autolite Pro Series wires (i'm doubting those)

And As far as I know the cat is completly original. I'm hearing a little louder noise from the exhaust as of late, i think the mufflers are going on me

And as for seein the engine move, when i've looked I cant tell its really moving unless i place my hand on it

Well, hopefully we can help get you squared away this time around.

If the Iridiums are 41-101 thats OK. Not sure about the Autolite plug wires. Our engine has a thing about using aftermarket wires such as Bosch, Autolite and others. Something about the resistance per foot. The best wires to use are the AC Delco Premium Silicone 7mm wires. They have the lowest resistance per foot and will handle an ignition system to well over 6500 rpms.

The CAT convertor can cause problems ranging from misfires/cutoff, poor fuel economy, a surging affect when accelerating and poor idle, etc. With your mileage and being the original it would be suspect. Best thing to do is get an exhaust system backpressure test which will test for a clogged or partially clogged CAT convertor. However, for the cost it would be cheaper just to get an aftermarket hi-flow like a Magnaflow and have it installed by a mom & pop muffler shop.

If the engine moves really bad that means you have a bad wishbone front mount(s), however, that would be quite obvious to the naked eye. A little flexing when watching and revving the engine is normal.

Other suggestion would be to clean the throttle body, especially the IAC sensor and seat with STP throttle body cleaner. Clean the inlet screen. Clean the MAF sensor hot wire element with electrical contact cleaner or spray MAF sensor cleaner. Make sure all the vacuum lines are good and tight.

From what I can see your engine shake is more like an ignition related misfire condition although it may not be triggering a SES light or any odb-ii DTC error code.

Hey graphicassult, hav you changed the fuel filter?

This might clear up your misfires or shaking of the motor. Thier can be subtle misfires that the SES wouldnt pick up on, caused by small particls in the fuel system.

Gm does recommend a fuel system flush(for $200 or so) at some interval, not exactly sure on the GP's interval, it wouldnt hurt to check in to it though.

Filter has been changed and fuel system flush has been done.

I dont think its a misfire to be honest, It dosent handle like its misfiring....

However sometimes after a long drive when i Start the vehicle it shakes for a minute or so, and sometimes when I start it after sitting awhile it will shake a bit...

I think i'll goto my dealer and get AcDelco Wires and then get a new cat...

Filter has been changed and fuel system flush has been done.

I dont think its a misfire to be honest, It dosent handle like its misfiring....

However sometimes after a long drive when i Start the vehicle it shakes for a minute or so, and sometimes when I start it after sitting awhile it will shake a bit...

I think i'll goto my dealer and get AcDelco Wires and then get a new cat...

Just to clarify on the shaking. Is the shaking there during cranking and before the engine fires up or when the engine has fired up and running? Or anything else you can clearly define. It is a weird problem.

Did you ever get the fuel pressure checked at the Schrader valve on the fuel pressure regulator to see if it is in specs?

The shaking is when the engine is running. I've never had it checked at the valve

probably transmission

How Do you figure transmission?

Trans would make since. Just vibrations from internals turnnig.
My GA SE does some fucky stuff like that too after a long driv or after I've been doging it hard.
Mostly at stops in gear, is that what yours is doing?

I had the same problem with my 2000 GP, turned out to be a clogged cat converter at 77000 miles (thank god for the 8yr/80000 on those).

I only had the problem for about 2 days before I got it fixed, but it caused my number 2 & 4 coils to go (which caused the misfire) and my O2 sensor to throw a code.

Cat cost me nothing (except for a week's waiting because the cat was misshipped), but the rest of the stuff cost me about $300. Dealer said that if I'd got it down there sooner, it wouldn't have ruined the coils. I don't know about that, but whatever it's done!

Just my thoughts,
Brick

I've had a coil go out on me! I think this might be my fix, it would make sense.

Low rpm=little pressure where as high rpm=high pressure which is why i only feel it at low because theres not a lot of pressure to force through, and its the OEM cat....

Graphicassult, Advance AUto, if you have one in your area, sells Delco wire sets WAY cheaper than a dealer. If you don't have anyone in your area besides a dealer that sells them, I'll get you a price quote on them when I get to work (I work at an AC-Delco distributor in Flint, MI). PM me if you're interested with your Zip Code and I can get you an exact quote including shipping.

The AC Delco part number is 746BB for the Premium Silicone 7mm wires. GM # 12192468.

Graphicassult, Advance AUto, if you have one in your area, sells Delco wire sets WAY cheaper than a dealer. If you don't have anyone in your area besides a dealer that sells them, I'll get you a price quote on them when I get to work (I work at an AC-Delco distributor in Flint, MI). PM me if you're interested with your Zip Code and I can get you an exact quote including shipping.


Sorry this isnt always true though. You do hav to shop around.
I checked for a thermostat at THe Zone and Advance auto(just outa curiosity) and they were $4 more then what I could get one from my local Pontiac dealershit. And those two places are prone to sell Old, bad thermostats. Just my :2cents:

7mm? those are kinda wimpy dont you think? :lol:

The thing with Advance is you have to wait and put a deposit on them to order them. And i have NO paitence, haha. Anyways i'll try wires and a new cat and see what I come up with

sounds like a vacuum leak if it happened after a repair like that you might of broken a line or got one hooked up wrong take some time to go over it and listen while it runs take a long peice of line stick it in your ear and move it over the engine while running and you will be able to hear it over the other noise or they are bad about carbon coming loose and getting stuck in the egr or if you had the egr off the car for a while as you repaired it it might of stuck on its own but anyway sounds like a loss at the intake air presure for sure

I had my valve cover gaskets replaced, i didnt do it myself.....vaccum leak?

i agree with bnaylor that it is probably the cat. if nothing else, get it checked at the dealer- they have an extended warranty for up to 120,000 miles. even if that is not the issue, you will have eliminated the problem. i had my cat replaced by the dealer on my s10 last week for FREE! it was 498.00 bucks worth of work that cost me nothing, and the kicker...the cat wasnt even the problem!!! so if nothing else you can get one problem out of the way or get a free cat!
by the way- did you replace the injector ?