Thread: GTP Troubles - Big time

I started having issues with my '00 GTP a few weeks ago. First it would stumble/hesitate once or twice a day. Then it gradually got worse. To the point where it would just die when I came to a stop. Then it wouldn't idle no more than a minute before dying and making a pop noise.

I came here and searched and found that maybe the MAF was bad. I unplugged it idled and did not die. It was more drivable but it still sucked.

Codes I had stored were P0300 and both O2s

I put a fuel psi gauge on the rail, 43#, pulled pump assembly to verify no collapsed tube/hoses, cavitated sock... all looked good.

I fixed my blown out resinator with a piece of straight pipe welded in. I installed a new fuel filter, & post CAT O2 sensor. STILL SAME PROBLEMS.

I bought a new Duralast MAF sensor and installed it. It would not even rev past 2,000 RPM. Again, I unplugged it and it was drivable.

I tooK the sensor back to the store and got another one. SAME THING. unplugged it and it was drivable.

I bought a scan tool (actron cp9575) cleared the P0102 (from being unplugged) Plugged in the 2nd sensor and this is what I found.
@ idle. the MAF #s would jump around from .67 to 1.30 LB/M
FUEL trim short 4.x
FUEL TRIM LONG 16.X

I took back to the 2nd sensor and exchanged it for another one. SAME CRAP. unlplugged it, now it's sitting in the driveway.

I'm lost and need some help to where I go from here. Thanks in advance.

clean the TB, check for vac leaks.

The MAP "HG is reading 10-12 " at idle and 16-17" in drive... Is this in tolerance?

Fuel trims @ 16.4.

It's got a vac leak.

Check all the vacuum lines from the TB, to the fuel rail, to under the blower snout, back around to the MAP sensor. Bet that one is dry-rotted/broken...it's a common issue. Also check the other vac lines on the three line tree on top of the blower/boost bypass valve on the front...along with the EVAP line going from the solenoid on the back of the supercharger to the TB.

-19 to -20 at idle is where it needs to be, in drive will be 1-3 less.

Ok so my low vacuum #s and high fuel trim #s point toward a vacuum leak somewhere then?? Will this make the MAF #s bounce all over too?

Small zip ties can work in a pinch

Originally Posted by GTPJason

Tee under the snout is cracked all the down on the bottom side of course. I had to remove it to see it. Installing a new Tee. I hope this cleans it up.

advance auto had the best T's i could find, they were small white t's. add a inch or so of new vac line to each side of the T, and put it in place of the old one.

I fixed the Tee. Found the 90ddg rubber fitting under the MAP was split too, fixed it. Pulled every vacuum line/tube/,fitting and inspected. Still only 13.3 "hg
And stiil surges and dies at idle.... I'm lost.

Try reading your plugs and see if you can isolate any cylinders that are running lean. Maybe you have an injector going out on you. In the process of pulling your plugs you can take a good look at your wires too. Might reveal a problem with those.

You said both O2's threw codes, you replaced the rear one. The rear one is for reading only, the front effects your fueling. I'd suggest fixing the known issue with the front O2, then try unplugging the maf and whatever you do..don't use a duracrap.

Still only getting 13.3 "hg MAP. Car died on me every single time I came to a stop this morning.

Billboost37 - Thanks for your reply. I did not know that the front O2 effected fueling. O2 #s look ok. they bounce from 035 - 800 mv nicely. Could it still be bad?

I will order a sensor. My original MAF is absolutely junk. It just stops reading sometimes and sticks on a number like .21 lb/m or .68 or 1.3 and it will spike to 48.x at times during idle. What is a sure shot replacement MAF for these cars? I know on my Grand National I could not get a single reman MAF to read over 100 gr/s at WOT when it should be 255. The fix all for that is to convert to the LT1 Maf and use a "MAF translator" This fixed all my MAF headaches.

Thanks,

Originally Posted by Shmoke

Try reading your plugs and see if you can isolate any cylinders that are running lean. Maybe you have an injector going out on you. In the process of pulling your plugs you can take a good look at your wires too. Might reveal a problem with those.

I pulled 1 plug out and it looked okay (light brown, no crud). I replaced plugs this past Spring time along with new wires. I ohm'd the coil packs too. All in range. Do the ignition modules normally go out on these cars?

Thanks,

Originally Posted by GTPJason

Codes I had stored were P0300 and both O2s

You tell me if you need a sensor. Here's what you said, which isn't enough information for me to say anything except...you said there was a code and for some reason decided to replace one that does nothing bad except set a light.

On maf, I'd say hit up JY's, ebay or amazon. Get a delco/original.

Originally Posted by BillBoost37

You tell me if you need a sensor. Here's what you said, which isn't enough information for me to say anything except...you said there was a code and for some reason decided to replace one that does nothing bad except set a light.

On maf, I'd say hit up JY's, ebay or amazon. Get a delco/original.

Thanks! Could the poor fueling cause the upstream O2 to throw a code if it's not reporting well? I will order a sensor and get it replaced, they aren't that expensive. Then I can rule out that. I guess I need to understand more how this engine management system works. Like Open loop/closed loop fueling and what sensors control fueling and how.

Tell you what helps us ...a lot is knowing the code and the name of the code. Honestly, because if you say got a P0171 Lean bank 1, technically that's not an O2 code and you don't need a sensor. If you have an inactive code..then you want a sensor.

PS.. best way to learn is to have trouble, and look up the actual GM diagnostic on the code you find. I found gearchatter.com used to have all the pages from GM.

I took the car over to my Dads tonight and put his MAF on. It ran very well at idle and driving. So, I need a good MAF sensor now.

Update: I got a used MAF sensor installed and the car is running excellent. MAF #s are stable, fuel trim #s are good, and No CEL now for 40 miles.