Grand Prix no start mystery

[Sunspot]

1999 Grand Prix super charged gets towed into the shop. The kid has added alot of "Bling" junk to the motor, he just did intake gaskets and afterwards the car would start and then quit right away. You could keep it running by fluttering the gas pedal, but it would smoke some fierce black smoke. This is what i did from that point on.
Popped the scan tool on there and read the peramiters of all the sensors
No reading at the TPS
Removed TPS, saw nothing phsically wrong with it, plugged back in and then got correct reading
Still ran the same
Found major vacum leak at throttle body gasket (he didn't clean off all the old gasket)
Installed new throttle body gasket, cleaned throttle body and Idle speed motor
Still ran the same
Cleaned all 6 spark plugs
Still ran the same
Cleaned MAF sensor
Still the same
Fuel pressure is 50 psi
Bent tab 85 on FP speed relay
Now car would run for about a minute then slowly dye out again
Installed new Fuel Pump resister, put tab 85 back
Now I am able to drive car around the block, but then it would randomly just quit out on the road, it would restart and then a few minutes later quit again.
Pulled back to the shop and it idled for as long as I wanted
Has a randlom misfire on cylinder 3
Misfire slowly got better on its own
Car would run great other that the random stall at this point
All sensors read within peramiters, NO CODES
Parked it behind the shop Saturday
Went out to start it on Tuesday morning hoping to figure out the random stall
Now the car won't start at all
Still No Codes, good fuel pressure, has spark, turns over, won't fire
What the hell happened between Sat. and Tues. (about 30 degrees outside both days)
This job is going backwards on me and I would appreciate any help, please!!!

[Sunspot]

I should mention it is a 3800, has MSD coil packs, K/N filter kit, high performance new spark plug wires, iridium plugs, new PCV

Please help!!!!!
sorry ahead of time for other info that i didn't post, let me know

[Mickey#1]

Some have found a crack in the flexible EGR tube after changing gaskets. They seem to get brittle with age. Did you do a compression check?

[BNaylor]

Originally Posted by Sunspot

Cleaned MAF sensor

What happens when you unplug the MAF sensor and then test drive it? Most of the time cleaning the MAF sensor wire element/thermistors won't help if the MAF sensor is bad.

[Sunspot]

No Change with MAF plugged in or unplugged, when car was running MAF was reading perfect on scan tool.
As far as the EGR tube, would that make it not run? after it was running before?
Please keep ideas coming

[Sunspot]

As for the compression check, no, the car ran great with no misfires before I parked it Saturday
I noticed today that the spark may be weak, not sure, just going by color. Has performance coil packs, so I would think the spark should be better than original?
Anyway, I am starting to lean towards a computer problem??????
Time is of the essance, thanks

[Mickey#1]

The EGR tube would have to have a very large crack to prevent starting but it's possible. There's also a vacuum port under the supercarger nose. They also break easily so take a look there. You mentioned cleaning the plugs & a miisfire that cleared up after running for a while. I'd go with new plugs but try starting before removing the old ones. Knowing if the plugs are wet or dry could help narrow this down.

PS - Did he change the gaskets as preventive maintenance or was he already having a problem?

[Sunspot]

He said, of coarse, that the car was running great, he just had the usual intake gasket leaks. I figured he probably didn't do the job exactly right, but the fact that I had the thing running pretty good for a while is throwing me off here. I swear there is a Gremlin in there. I will check those vacum spots, maybe I should pull the super charger and check his work.
One other thought is that I got the car running in a warm shop, pulled it outside to idle and even drove it around a bit (with the intermittent stal). I never pulled it back in the shop on that Saturday and parked it out back for the weekend. On Tuesday I went to start it and have the no start problem now. Maybe I should push it back in the shop and warm it up a bit? What would be so temperature sensative like that though?
Thanks for replys!!!

[tblake]

Maybe he didn't plug the coolant temp sensor back in, or its wires were melted to the exhaust crossover.

My money is on a leaky supercharger gasket. If he didn't scrape all the old gasket off the throttle body, then chances are its the same for the supercharger gasket. BTW, what person removes a throttle body to do LIM gaskets on the 3800? (amatuers)

Did you by chance notice the fuel trim numbers when you had it on the scan tool?

[grandprixgtx00]

Originally Posted by tblake

BTW, what person removes a throttle body to do LIM gaskets on the 3800? (amatuers)

LOL

[Sunspot]

I guess he had a performance throttle body he tried to put on, then changed his mind.
Anyway, we must remember that the car ran when I parked it, so I had made some progress with the car before the current situation. Would parking it outside make the supercharger leak more than inside? and could it leak enough to make it not even pop now? What about the weak spark?
I need the "Dr. House" of car diagnostics!!!!

[BNaylor]

Originally Posted by tblake

BTW, what person removes a throttle body to do LIM gaskets on the 3800? (amatuers)

......

I do since I replace the throttle body gasket on these type jobs. If you do LIM gaskets makes sense to do all intake related gaskets or seals. Of course during disassembly I leave the throttle body on until I remove the supercharger or UIM plenum on the NA SII 3800.


For weak spark have you tested the coil packs? Primary and secondary resistance. Have the ICM module checked and check the electrical connector/wiring to the ICM and the crank and cam position sensors. Check the ICM ground wire.

[Sunspot]

Scan tool shows cam and crank signals. He put on the new MSD coil packs, how do you test them? What should fuel trims read? ICM = Idle Control Motor, it shows reading right on the scan tool.
thanks for the help

[Mickey#1]

You can pull the spark plug wires off the coils & crank it over. The spark is strong enough to jump the gap on the coil towers. If the spark makes that jump but looks weak at the spark plugs then change the plugs. A plug can fire outside the cylinder but not fire under compression with the rich cold start fuel mixture. Don't use Bosch spark plugs in these engines!

ICM = Ignition Control Module. It's the module the coils are mounted to.

Fuel trims should read around zero. Engine has to be running.

[tblake]

In his MOD frenzy to the motor, did he replace the injectors, possibly as he was doing the LIM gaskets?

If so, the PCM needs to be tuned for the larger injectors.

This one is a head scratcher. Especially since you don't know even if he put the LIM gaskets in right.