2001 Pontiac GTP Supercharged 3.8 liter Dying and misfire !!

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#1
Hey guys.....

2001 GTP having a very strange issue. Maybe someone has come across this.

It would not start when first braough in. Complaint was stalled when put in gear. After I got it started. It ran smooth for about 3 mn and started Chugging and bucking. Black smoke out the pipe and died. Limped it to the garage and began to look it over. Scaned and found EGR Code.Stuck Pintle position. Figures it was making the thing run like crap and killing the engine. Checked fuel pressure. Spec is 48 to 59 according to Chiltons and Mitchell. Car has 48 KOEO and 52 running when it does run. 55 with regulater vacumn removed.

Found misfire counts all over the place so started to look at ignition,plugs and wires. Ciols all fire across with wires off and it is a strong spark.

I did replace the Cat because it showed low flow. 178K on the car. The only thing I see on the scanner that troubles me is the Boost % is at 100 when it does run. Figuring it reads backwards from normal when boosting on the scanner. Lower percent more boost ect.

I did swap out the Map sensor, Ignition Control Modual and still have the same issue. Idles for about 3 or 4 min and then bucks, chugs and dies. Will not start unless you open throttle plate to about 2.00 on TPS scale. Then it will fire and start to clean ouot like a flooded carburated car. All the injectors are fireing and not grounded.

anyone have this problem on these Super Charged 3.8 liters. I did notice the rear exhaust manifold gasket is leaking. It puffs black smoke when the car is trying to stay running through the computer control for idle.

Basically.. The GTP will start sometimes. run okay then start to act like it is flooding. Die and not restart. O2 sensors are switching 200 to 900 and Air fuel is 14.7 when this is all occuring... Injector pulse is 2.3 to 2.5 when running. Crankiing it is higher and seems to be working.

when it does die. Its like someone just shuts it off. You cant keep it running by opening throttle. It just shuts off.

Spark is present when this occurs. Snap On spark tester shows spark when its dying.

Matt :mad:
 

billr

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#2
Have you been able to observe fuel pressure just as it goes rich and dies? Even harder to catch, how about the injector pulse-width as it dies?
 

nickb2

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#4
I would love to see ECT value at stall moment, what type of scanner are you using, would like to know to figure what you can check with it, what are the fuel trims reading? (fuel adaptive %) Obviously fuel related. Interesting post, keep us in the know, plz. 8)
 
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#5
Okay.. I actually got to drive it for the first time in 2 days...

Injector pulse width when in park and running is 2.0 and when it starts to die it will run up to about 8.0 to 10.0 . I did see a flash of a value of 0.0 and then 28.0 to 34.0 for a split second.

Fuel pressure is running at 48. Snap throttle pressue 48 to 55. When it starts to die. The fuel pressure will rise to about 52. I just fond out from GM that the fuel spec should be 52 - 59 for that Vin 1 engine.

While driving it... It will run smooth until 3200 rpm and then start cutting out. If you keep your foot in it it will not accelerate and it dies completley. Fuel pressure gauge hooked up and riding on the windshield reads 52 to 55 when driving WOT with the cutting out. Normal cruising speeds below 3200 RPM it did not cut out. Also noticed in park or nuetral . If you WOT to the Rev Limiter. It will Limit for a few seconds than go to 6,000 RPM and back to chugging and dying...

This cant be the dang fuel pump can it ??? Someone told the guy that owns the car that the negative battery cable could be bad... He googled it last night and asked some questions...

Matt
 

billr

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#6
I'm guessing here, but I think the fuel pressure (and pump) are OK. Those injector pulse-widths seem very long, like it is at WOT with full turbo boost; and that is what it seems your scanner is indicating. I think it is related to MAP, can you read that directly when it is dying? Are you sure you swapped in the correct MAP sensor, one for turbo boost?
 

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#7
You say you replaced the cat....it sure sounds like a blocked exhaust......it's possible it could be plugged after the cat.....

I would pull the O2 sensor before the cat to open up the system, and see if the car runs better......if it does, install the O2 sensor, then open the flange after the cat to see how the car runs....
 
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#8
I think I got the right MAP . BWD brand and gave them the VIN 1 Supercharged detail...

The Trim readings are -4 and 11 when dieing. 20 and 16 when running fine.

Map kpa is 29 Volts .53 running. When it died last time.. Trim went to -22% and 7.8

Fuel pressure is pretty much staying at or between 48 and 52. 55 when WOT ...

when I go againts the limiter and then hold it just below it. 3800 RPM. It will stay there for a bit and then die. Cut out and act like your turning the ignition off. But there is still spark present.

Maybe I will try another MAP sensor. Also have EGR Code back. P1404 and now a P1107 This is after I drove it and it died and was cutting out. It wont stay running again now unless you hold the throttle open... This is a weird one...

Matt
 
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#9
Gus....

I will give that a try with the exhaust. It does seem to flow real slow out the back at idle.

Maybe the Muffler is plugged up. I will be surprised if that is the case. i started the car with the flange open at the end of the cat when I replaced it. It still was acting up... I will test it again...

Matt
 
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#11
Done for today on this one.... Going home... Went out to move it and now it wont even stay running... Looked at the pulse width while it would fire and die. It was going as high as 43.0....

Open loop O2 sensors reading between 300 - 600 ....

After holding the throttle open a little and getting it to run it was able to stay running but flooding .. The exhaust smeels like a burning cat when it is loading up. Probably do to the over fuel condition. It does blow black coal out the back when its loading up.

talk to you guys tomorrow... Over and out for tonight...
 

nickb2

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#12
I always like diagnosing and eliminating before throwing parts at a car. As gus said, check for a possible exhaust restriction and also I post here a bit of info to understand what fuel trim does and how it is related to misfires. Very useful in diagnosis. Start taking measurements here, vacuum would be nice also, very underrated in today's cars. Ppl seem to be afraid of a good ole vac gauge.
Fuel Trim Diagnostics
To maintain the correct air/fuel mixture, the PCM adjusts Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Both of these values can be read on a scan tool that can display OBD II system data, and may be used to diagnose fuel-related problems.

Normal range for both STFT and LTFT is typically plus or minus 8. If the numbers are +10 or higher for STFT and LTFT, the engine is running LEAN (not enough fuel). If the values for both STFT and LTFT are both minus 10 or more, the engine is running RICH (too much fuel).

Vacuum leaks can create a lean-running engine that requires extra fuel to balance the fuel mixture. If you rev the engine to 1500 to 2000 rpm and hold it for a minute or so, and the STFT value drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. If the STFT value does not change much, the lean fuel condition is more likely a fuel delivery problem (weak fuel pump, restricted fuel filter, dirty fuel injectors or a leaky fuel pressure regulator) than a vacuum leak.

Would be great to see those numbers matched to a trim definition such a LTFT=, STFT=. Have you forgotten my ECT request, essential to diagnosing this kind of problem. I will assume readings are -4 STFT and 11 LTFT at first stall and 20 STFT and 16LTFT running. With this last reading I see a manifold vacuum leak as a big possibility, included in possible causes for this type of reading you see misfires (which you have) and low fuel pressure,(which you somewhat have according to you) and mostly vacuum leaks.
 
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#13
Nick,

I am on the same page as you. I am seeing the fuel trim going all over the place. I was suspecting a manifold gasket leak. Being superchaged and with as many miles on it. I can see that it would push out the manifold gasket. I cant hear any leaks but I will further investigate that later today.

The ECT ( Engine Collant Temp ) Is what you are refering to I assume. I forgot to check that. I assume the one for the computer.

As for the lean rich condition. It seems lean when it does run. As a matter of fact. I can induce a vacumn leak and it will idle and run a little better. Until it starts cutting out and flooding. It is intermittent as well.

This morning it would not even start. Crank start stall. Until I held the throttle open to 2.00 on the TPS Reading. Just cracking it. It then would start and die as soon as I released the throttle.

After 4 tries. It then staed running long enough to move it aroun and within 3 min. It started to flood out and stall again.

Wont be able to check it out till late this afternoon. Got slammed with Cold Weather repairs this morning and trying to catch that up.

I will check in soon. Thanks a TON Guys !!!!

Matt
 
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#14
Hey Nick

Not really throwing parts at the car yet... Just the cat because it was plugged up. Low flow and a lot of back pressure. I had the ICM and did By the MAP.

The ECT readings at shop temp engine cold is 2364 . It wont stay running this morning at all... Only once I got it to run and then it started dying within 2 min...

Matt
 
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#15
STF =20 LTF = 16 when running normal.

Dying SFT= -25 LTF= 0

Then it dies.

on restart SFT = 0 LTF= -13

2000 rpm when running stays at 20 and 16 . When dieing at 2000 rpm (Chugging and misfire) STF= -35 LTF= 0 Fuel pressure bouncing from 48 to 54 lbs.....

Give or take a little on each.

I am seriousley thinking the dang fuel pump is causing all this. I have a pressure pump I can hook to the Shcrader and set at recommended pressure .If the dang thing runs after I hook this up and feed pressure to the rail then I know its the pump....

Matt