99 gran prix 3800II help please

[72240z]

I'm a mechanic myself but this one has me stumped. In the past I have always had a AF result pop up when I google problems so this time I decided to finally sign up and post myself. Did a quick search 1st to make sure not to waste anyone's time but nothing quite matches this problem.


At any rpm and mph, both hot and cold the engine will cut all power and return to aprox idle engine speed (600-1000rpm). You can press the gas pedal but nothing happens, this is for about 1-5 seconds then the rpms hick up (slight surge) and all is well again. It has happened about 10-15 times both right after start up and after driving a good 30min, only once of those times did it stall out completely. It does not happen at idle and the idle is steady and correct.There is no electrical power loss at the time it happens. There is also no codes being set off at any time.

I realize the issue is indicative of many things that could cause it but I'm hoping a pontiac pro on here can help me narrow it down a bit. Not looking for anything spoon fed, just some ideas would be great. Right now I'm thinking either pcm, something ignition related or a intake leak because those are the only things I can think of that would cause this problem and not set off a code.

I appreciate any help you guys can throw my way, thank you.
Jason

[inafogg]

just because.........check the vacuum line to the map sensor.had simular but on a G/AM

[richtazz]

With the key off, try unplugging the MAF sensor and leaving it unplugged. If the car runs better, the MAF is bad. Many times a MAF will cause issues like yours and not trip any codes.

[72240z]

Okay thanks for the responses guys.

Checked the vac lines, couldn't find a leak.
Checked the maf, it's way worse unpluged, no change when I shake it either.
Checked the resistance at the primary and secondary points on all the coils.
Checked the wires.
Plugs have maybe 5k miles on them and look alright, engine has definately looks like it's been leaning out though. Plugs have a slight white color to them. Not enough to worry me but enough to be noteworthy.
Fuel pump and filter has maybe 20k on them.
Map sensor is new.
Checked the tps.

All the work has been done by me it's my mothers car.

Today while problem solving it I realized it has gotten much worse. It still will be fine in park and in neutral. The problem only happen under load. I also noticed its at 2-2.5k rpms every time. If you go gradually you can get to 2.5k then it will cut and fight to try not to stall out, then hickup to say 1.5k rpm and be okay. If you gun it the rpms get to maybe 2k and it just dies and stalls out. It does it every time now.

I hope this update helps someone to help me. I'm a machanic but I am young and this has my stumped. Please help me get my mother off my back :-).

Thanks for the help thus far.

[GTP Dad]

Did you check the fuel pressure to see if the pressure is correct. Based on your observations it sounds like there may be a problem with either the fuel pump relay or the fuel pressure regulator. Check the fuel pressure while you are driving and see what happens.

[tblake]

Have you scanned it for DTC's?

When it stalls out does the "trac off" light illuminate?

For some reason I still like Rich's idea and think it sounds like a bad MAF. You say it ran worse unplugged, and no change when you "shook it"? Not to sound like a smart @$$, but how do you mean by shake it? It almost sounds like we are thinking about different sensors.

Here is the MAF sensor. (photo compliments of bnaylor)

[72240z]

Yes the 1st thing I did was scan it, it's not throwing any codes.

That light so far has not come on when it stalls.

You can sound like a smart ass if you want so long as it's trying to be helpful lol. I'm aware of what the maf is though, on nissans/infinity and some fords/jags etc when a maf is going, shaking it is a field test. On one that is failing the rpms will dip or rise when you do.

Unplugged it was almost undriveable. Bogging when you touch the accelerator and stalling out constantly. If you guys really think its the maf I have no prob giving it more attention. Does anyone have the factory check procedure? My domestics alldata cd for this year is out on loan.

Any other ideas as well?

Thanks everyone, the help is appreciated.

[richtazz]

Did you unplug the MAF while it was running (incorrect method), or did you shut the car off, unplug the MAF leaving it unplugged, then restart the car (correct method)? With the MAF unplugged, the CEL should come on due to it being unplugged. If it didn't you may have other issues like a bad PCM or bad wiring.

[72240z]

I unpluged the maf with the car off, Then started it and took it for a test drive. The exact same problem symptoms are there only it stalls easier and will start and immediately stall every time after until I plug the maf back in. I just now did it a 2nd time to make sure before I posted this.

The check engine light however did not click on for the maf either time I did it. Maybe I didn't give it enough time or maybe there is a problem? The wiring is in good shape, the car only has 100k miles on it. If it's the computer I'd be very disappointing in GM.

While I was checking today I also unplugged the egr, also no change.

Any fresh ideas based on this? Thanks

[tblake]

Pull the vacuum hose off the FPR, prime the engine, and check to see if gas dribbles out.

Has the Crank Position sensor ever been replaced? If not, you may just want to replace it just to rule it out. Mine went bad at 80,000 miles causing the car to stall out of nowhere. RPM's would just drop and car would die. Replaced it in about 1.5 hours in my garage and it has been fine ever since. The dealership part was only 45.00 bucks.

However a MAF to throw at it is going to be spendy. They run about 350.00. I'm betting you did not let it run long enough with it unplugged. I would try it again. Unplug it, start it, let the idle stabilize for a few minutes, and take it for a spin.

[72240z]

Okay that will be my next round of tests.

You know I really have a bad feeling about the fuel pressure. Like maybe it's leaning out. I used to have a guage with a really long hose so I could tape it to the windshield but someone broke it on me. The way the rpms die out and how the plugs show that little bit or white after only a few weeks makes me think it may be that.

Also today while spraying with carb cleaner againt to check for vac leaks I noticed a white film around the pulleys and of course the cas. When I asked my mom what it was she said her boyfriend (Who knows NOTHING of cars) decided to soak them all with lithium grease because he heard a squeak. That plus what you describe as your past experience with a bad cas makes me think that could be a possibility too.

It wouldn't throw a code if it was bad?

I didn't know it was only 40 dollars if it can be bad without throwing a code maybe I'll pick one up. Like you said just to rule it out. Seems like now or later I'll be replacing it anyway.

Thank you

[richtazz]

Do you have a scan tool that can monitor live data or just a code reader? If your scan tool can monitor live data, watch your cam and crank sensor signal readings when it hiccups. From what you're describing, it doesn't sound like a CKPS to me, but odder things have happened. Typical CKPS symptoms include tach dropping near zero just before stalling along with the trac-off light coming on (due to the CKPS being used in the traction control system).

[72240z]

I have a scan tool that can monitor but the cas must be a code if its in the live data stream. There are maybe 3 that I can't identify in there that are just numbers and letter. I'll look them up and see what I see.

The tach drops off fast and very close to 0 as it tried to recover then stalls. The trac-off light never comes on though I even checked again to see. It's usually always off but I turned it on to see if it would kick on at stall.

The new thing though is that its just flat out stalling all the time now. I start it, it stalls, again, again, then it will stay running, idle fine, drive 20 feet, stall, start, stall, start, stall, drive 50 feet, stall etc....

I'm going to take a vid of it happening and upload/link it because I'm flat out frustrated and at a loss here. My mom needs her car and I need her off my back.

If anyone has anymore opinions or ideas please keep them coming. I really appreciate the help greatly.

[GTP Version 2.0]

Have you physically inspected the PCM yet? mainly the connections and wiring. I would almost suggest switching out the PCM if you have another just to eliminate that. With the irregularity of problems I can't help but wonder if the harness is bad. Since your moms boyfriend put white lithium grease on the pulley maybe he put in on the wiring connections thinking its dielectric grease? Let us know.

[richtazz]

Because you're not getting a CEL when the MAF is unplugged (and you should as soon as you start the car), I'm with GTP Version 2.0that your problem lies with the PCM or the wiring harness(es) associated with it.