99 gran prix 3800II help please

[tblake]

I hate to go against the grain here, but if it were me I would throw in a new Crank Position Sensor. That problem sounds familiar. If nothing else the Crank Sensor is about shot anyways with 80,000 miles.

What does your scan tool indicate the RPM's are when the car stalls out?

Stupid question, is this a supercharged 3800? Is so, you may want to give the fuel resistor bypass a shot. Check out the tips and maintenance subforum.

[72240z]

I picked up a new fuel pressure tester today and gave it a go. Had someone get the car to stutter to a stall while in park by quick giving it gas then again. The fuel pressure dropped to like 5-10psi as it stutters at about 200-600rpm. That can't be good. At idle its at 40-45 (needle vibration), I think thats just at the bottom of spec. It's odd though the fuel pressure reg didnt spit fuel out the vac line, the pump is new, the filter is new, I drained the tank when I installed them as the car had been sitting a few months. Idk why the pressure would be doing that unless something is cutting it? Voltage to the pump checks out fine.

I forgot to check the highest psi at prime, tomorrow I'll check.

When the rpms are responding normally while parked it will only go down to about 20psi at 4k rpm. I can't test it under load until I work out a longer hose like my old one.

I did a ground/voltage check too and found I was loosing a hell of a lot of voltage. I had 12.8 at the bat and 3.4 on the engine mount. Got a bad ohm reading from the bat to the ground mount. I noticed that GM decided to install the ground over the paint, pretty smart design. Sanded the area cleaned everything up and got full voltage again. It didn't fix the prob but good none the less.

When I test drove it to see if the ground issue was anything and it stalled out on me 8 times (in a blocks distance ugh), ONE time the traction off light came one.

What are your opinions on that fuel pressure outcome? Or the light coming on just the one time? Isn't there a resistance test for that cas instead of me just throwing money at one?

I'm impressed you guys have stuck with me as long as you have and not just moved on. Thank you again very much. I'll be sure to pay it forward on here on makes I'm better acquainted with after this is settled.

[richtazz]

Did you re-test fuel pressure once you got the ground issue fixed? It should be 48-55psi key on/engine off and should drop 3-10psi when the car is at idle with vacuum attached to the fpr, then if you disconnect vacuum at the FPR, it should shoot up to close to key on/engine off spec.

I still say the PCM and or it's wiring is the biggest suspect since no CEL appeared when you disconnected the MAF and started/drove the car.

[72240z]

The fuel system checks out, its 50psi in the "on" position and 42psi at idle. When I take the vacuum line off the fpr it does shoot back up to like 50-55psi.

I took a vid of the symptom in park. Couldn't do it under load as I hate vid taping and driving, after all the bitching I do about cell phone users it would make me a hypocrite hah. I think the vid is good though. The trac off light comes on after every stall now, it wasn't doing that before.

http://www.youtube.com/watch?v=-04FTRzbANQ

You can hear when I'm pressing the petal to cause the problem and when I'm not and the engine just takes off in the rpm on it's own.

Let me know what you guys think

Also, I'm not ignoring the fact no check light comes on with the maf unplugged, I checked again today. I just want to save testing and in turn buying a new ecu until last.

Thanks again

[tblake]

Originally Posted by 72240z

.....The trac off light comes on after every stall now, it wasn't doing that before....

Uh Oh! You know what that means! Time for a Crankshaft Position Sensor....

http://www.automotiveforums.com/vbul...d.php?t=652664

[72240z]

Did you watch the vid? It comes on for the next start after stall. I mean if thats what it is amen because its the cheapest of the options. Not the easiest but Whatever so long as it's locked down and I can fix it I'm happy. I never have a problem with labor it's diagnosing that frustrates the hell out me. I'm only 25yo I kind of assume(hope) it gets easier the older you get haha.

Sure cas? Case closed?



I'll pick one up tomorrow. Thank you everyone.

[tblake]

I am standing by a Crank Position Sensor, but Rich could be right with a PCM issue.

Make sure if you get a CKPS sensor, its a delco, and you may have to do a case learn when you are done with it to. I didn't have to, but you might. Its always a possibility.

[richtazz]

I hope for your sake it is a CKPS and replacing it stops the stalling. It's much cheaper and easier to replace than a PCM, but the no-CEL with the MAF unplugged is an issue you're going to have to address at some point.

[tblake]

You think Rich? A pcm is cheaper than a crank position sensor? I just wonder if he didn't leave it run long enough with the MAF disconnected to trip the ses.

[72240z]

I picked up the cas today, it's free since I know the manager. I'll try and get to it tom.


No light coming on when the maf is disconnected really is disconcerting. It's also a little frustrating I cant find a check procedure for it or the ecu either. I tried unplugging it 3 times the last time I let it idle maybe 5min and drove it up and down my dead end street once. Only once because it's down right undriveable unplugged. Honestly that should have been enough no? The tps unplugged threw 2 coded in about a min.

I'll just keep an eye out for one at the junk yard or something because I cant shell out that kind of money just to see.

Really hope the cas fixes the stall prob. Then I'll just start checking grounds and connections to the maf at my leisure.

Are the grounds multiplexed on this?

[richtazz]

Originally Posted by tblake

You think Rich? A pcm is cheaper than a crank position sensor? I just wonder if he didn't leave it run long enough with the MAF disconnected to trip the ses.

No, other way around Tim, a CKPS is much cheaper and easier to install than a PCM is for sure. I think maybe you read that wrong.

Any time I've ever done the unplug test with a MAF, it tripped the CEL almost immediately whether the car was warmed up or stone cold.

[tblake]

Yeah, sorry now that I read it again....

I unplugged mine and like you said the SES light came on within a block of driving.

I think its odd in his video that he is able to keep it running by giving it gas. SOmething not consistant with a bad CPS. I just don't know.

If he had a way of watching the data stream, he could check out the MAF frequency as it idles and is being revved up.

[72240z]

I can't keep it running by reving it. If you listen I hit the petal fast a few times to force the stall out. When it revs up like that its doing it on it's own trying to recover. Once the idle drops I'm no longer touching the petal at all.

I do have a way to read it, the scan tool. It checks out just fine in the live data. I have no tool to test accuracy but its consistent throughout the rpm range.

[richtazz]

how do the TPS readings look as you ease down and back up on the accellerator pedal (do this with the key on and engine off)? Do the numbers rise and fall steadily, or do they jump large amounts at a time. What are your short and long term fuel trim values?

[72240z]

I just got done changing the cas, it's not that. The problem is still there and worse if anything. The tps seems steady and accurate. I'm really starting to suspect the fuel pump I put in a couple months ago is defective or bad in some way. The fuel pressure dumps every time the car stalls. When it shudders like its going to stall the pressure has dropped to nil then when the rpms shoot back up the pressure follows suite. The key in the on pos pressure and the regulator pressure change both check out, I checked again. Maybe the pump just can't handle load and is getting worse and worse.

On the 1st test drive it stalled out and would start and imediately stall, like 20 times it took before I could put it in gear then it stalled 3 sec later, then 10more times of start and stall until I could get it in gear again and 50feet back to my driveway.

Opinions?