2002 Grand Prix 3.8 V6 stumbling, barely runs - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-19-2008, 05:49 AM   #1
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Default 2002 Grand Prix 3.8 V6 stumbling, barely runs

I realize this is a bonneville forum, but I have found much information about the LIM and UIM through search engines and recognize guys you as very knowledgable guys on the 3.8 v6. Please do not discriminate because it is a grand prix :(

Help! The car has 65k miles on it, and I have been trying to figure out what is wrong with it.. The symptoms are as follows:

Car has vibration, like misfire or something
Car tends to free-rev at high rpms, sometimes lagging on gear change
When at W.O.T. and the transmission down shifts the car will free rev at 4k-5k.
Car throws no codes
Sometimes will make a slight hissing sound when w.o.t. and missing
No power, or acceleration.. for about 2% of throttle it will feel somewhat smooth, but with any acceleration or load at all it feels like it will barely make it. It will still move from point a from point b, but is a rough, and I feel it could be damaging to the car.

I have checked the plugs/wires, and I have checked the fuel pressure. I have made sure all sensors were plugged in and nothing was burnt.

Currently, the car had a slight oil leak from LIM on passenger side. I replaced the LIM and UIM w/ the APN intake w/ the smaller egr pipe. The car no longer leaks, and the upper and lower intake are perfect.

I have access to a 99 which has a 3.8 V6 series ii that is a oldsmobile delta or somethign to that effect. I was wondering, are any of the items the same? The coil packs and all look the same to me. I was considering swapping some of the sensors off it to see if I can troubleshoot the problem.

Any idea'* would be most helpful.. the car has been down for 2 months, and a single mother is stranded without her car. I am simply hoping to fix it for her to get back on the road.. I am very worried, because her child was extremely ill and she had no ride! She just got the car paid off, and is at a loss for what to do since it is out of warranty.

The car has overheated in the past for 3-5 minutes, but ran fine after the fact. It has developed this problem a month or more later. So I am not sure if it is related :(

What are some things I can check if they are compatible from the 99 3.8, and what are are some idea'* for things to look at. The lady simply cannot afford a buy it and guess solution. Some common sense and troubleshooting idea'* would be a great help from you guys.

I do have a fluke multimeter, to test values on parts.

I very very very much appreciate any/all help you can give.

Thanks,
Josh
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Old 03-19-2008, 11:21 AM   #2
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Virtually all of the parts from the Olds could be swapped over for a test. You said that you checked the plugs and wires? What did you do to check them? What was the fuel pressure?

What happens if you disconnect the MAF sensor (the black rectangular box shaped thing on the throttle body)? Does it smooth out at all? Have you checked for vacuum leaks? What caused the overheating? Any of the posts on the coil packs rusted?

I know...lots of questions, but the answers will help us hopefully lead you in the right direction.
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Old 03-20-2008, 01:53 AM   #3
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Quote:
Originally Posted by Archon
Virtually all of the parts from the Olds could be swapped over for a test. You said that you checked the plugs and wires? What did you do to check them? What was the fuel pressure?

What happens if you disconnect the MAF sensor (the black rectangular box shaped thing on the throttle body)? Does it smooth out at all? Have you checked for vacuum leaks? What caused the overheating? Any of the posts on the coil packs rusted?

I know...lots of questions, but the answers will help us hopefully lead you in the right direction.
Archon,

Thanks for the reply

The fuel pressure was in the 50'*, it dropped some when i'd hold the break and put a little load on the car.. but not alot.. just a couple of psi.

I changed the plugs and wires all together, then also tested each one unplugged from the cylinder and grounded for a solid spark.

I do not know why it overheated, I'll have to ask her.. I believe it was the radiator.

I don't hear any audible vacuum leaks.. It doesn't rev up by it'* own or take a long time to come to idle or have any characteristics of a bad vacuum leak.. but I'm not sure. Can I just spray starting fluid to find it?

I will check the coil packs, but I doubt it. I will be trading ones from another vehicle though to help eliminate..

I will go outside also now and unplug the maf sensor, etc.

I will post back the results.

Thanks
Josh
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Old 03-20-2008, 02:27 AM   #4
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I unplugged the maf sensor.. the car picked up a bunch of power, but if you floored it, it still free revved.

Maybe it'* a combination of things..

I think the MAF makes the car semi-drivable though, so long as you don't get in a bind and need to give it some gas.

Is there a possibility the PCM is bad?

Josh
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Old 03-20-2008, 11:36 AM   #5
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It likely is a couple of different things. As the MAF appears to be one, you can try cleaning it first. Remove it, and carefully clean the wires with alcohol, and a Q tips. Twist the fibers tight on the Q tip before cleaning the wires. Or you can buy some MAF cleaner from an auto parts store. Be certain that it is MAF cleaner, as others can cause problems. If that doesn't take care of the problem, then replacement will likely be needed.

The free-revving is likely the transmission. Check the level and condition of the fluid. Check after it is warmed up, in park, and the engine running. Is the level good? What is the color? Bright red, or more toward a brown color? How does it smell? Does it have a burned smell to it? While the PCM is possible, it'* more toward the bottom of the list, than the top.
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Old 03-20-2008, 04:48 PM   #6
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Quote:
Originally Posted by Archon
It likely is a couple of different things. As the MAF appears to be one, you can try cleaning it first. Remove it, and carefully clean the wires with alcohol, and a Q tips. Twist the fibers tight on the Q tip before cleaning the wires. Or you can buy some MAF cleaner from an auto parts store. Be certain that it is MAF cleaner, as others can cause problems. If that doesn't take care of the problem, then replacement will likely be needed.

The free-revving is likely the transmission. Check the level and condition of the fluid. Check after it is warmed up, in park, and the engine running. Is the level good? What is the color? Bright red, or more toward a brown color? How does it smell? Does it have a burned smell to it? While the PCM is possible, it'* more toward the bottom of the list, than the top.
I will be cleaning the MAF tonight, likely. I'm not sure it'* the transmission, it shifts beautifully otherwise than W.O.T... and the transmission feels like it downshifts.. there just isn't any power whatsoever.. the motor nearly cuts off. My first instinct was that, but I think that the transmission is doing it'* just, the motor just barely runs above 3000 rpm, even driving in one gear.. it dies out.

The MAF made it feel a lot less like it'* stumbling below 2500 or so, and actually pick up and accelerate a little.. although it still feels way down on power..

I will be inspecting the transmission, just in case..

Here is a list of things I am going to try swapping on Saturday:

Ignition control module, coil packs, and map sensor.

Is there anything else you would recommend testing while I have the other car to test from.

Josh
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Old 03-21-2008, 01:37 PM   #7
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Perhaps we need a definition of "free-rev"? That would be where the engine increases in speed, but there is no corresponding increase in vehicle speed. It would be like you shifted into neutral. Is that what we're talking about here? If so, there aren't many other suspects than the transmission for that.

As things improved when you disconnected the MAF - check the number on the MAF from the donor car, and if that matches the one in the GP, try swapping them and see if things improve.
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Old 03-23-2008, 05:10 AM   #8
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Quote:
Originally Posted by Archon
Perhaps we need a definition of "free-rev"? That would be where the engine increases in speed, but there is no corresponding increase in vehicle speed. It would be like you shifted into neutral. Is that what we're talking about here? If so, there aren't many other suspects than the transmission for that.

As things improved when you disconnected the MAF - check the number on the MAF from the donor car, and if that matches the one in the GP, try swapping them and see if things improve.
Let me rephrase free rev.

It does not want to pull.. it feels electrical, because I hear some swooshing sounds sometimes and it is at precisely the same rpms regardless of temperature. It does it in manual 1st gear with no gear change, 2nd, or 3rd.. so it'* not slippage, because the tranny isn't shifting. When I changed manually from 1st to second, regardless of rpm.. the tranny shifts like butter..

The reason I say free-rev is.. when you downshift, it goes directly to the right gear, and starts to pull.. but the motor makes no power at 3k-4k.. so it just revs up mechanically, but doesn't pull any..

The tranny fluid is fine, it is not burnt.. the tranny shifts perfectly.. the motor just doesn't pull above almost exactly 3k no matter the scenario.. during a shift, or just in the middle of a gear.

If there is a problem, I'd think it'd be electrical or something to that effect.. as the bands/clutches/etc are likely all fine considering how positively and smoothly it shifts.

So long as you don't go above 3k, it drives like a dream. At almost EXACTLY 3k, EVERY time, regardless of anything.. the motor just makes no power.

Do you still think it'* the transmission?

FWIW: I swapped ICM/coilpacks and map sensor with no luck.. still quit at exactly 3k.. regardless of the scenario.

I'd think the missing at 3k even in just 1 gear with no shift involved would rule out *MOST* transmission problems.

Josh
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Old 03-23-2008, 10:04 AM   #9
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Could be the catalytic convertor. Sometimes when bad they'll rattle if shaken or kicked. If it doesn't rattle then stand by the curb & have someone drive by in the 3-4000 rpm range. You might be able to hear a whooshing sound. Best test is to just take it to a muffler shop & have them check it. Many will do it for free.

Let'* not forget the other end, check the air filter.
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