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Old 07-30-2010, 10:56 AM   #1
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1991 Pontiac 6000 v6 3.1l running rough


Hey Guys,

I have a 1991 Pontiac 6000 with the 3.1 v6 and 3sp auto tranny. The past year, it has been running rougher and rougher. When cruising through town or at hwy speeds (between 35 and 55), it jerks back and forth. From what I understand, this is because the engine is running rough when torque converter is locked up, causing the "roughness" to transfer straight to the driveline. The other symptoms are a slight hesitation when you press the throttle, rough idle after warmed up, and sometimes when you let off the throttle in stop and go traffic, it nearly dies before sputtering and regaining its idle.

When the engine is cold, it isn't an issue. When it gets up to about operating temp after 8 to 10 minutes of driving, then it starts to run rough. I put an inline spark plug light on each plug wire while it experienced the miss, but I never noticed the inline light "missing" when the engine did.

I put a dollar bill behind the tail pipe. It flutters a little as expected when the engine is running. When it starts running rough, however, it doesn't suck the dollar bill back in, it actually "puffs" it out away from the tail pipe.

I'm not a mechanic, but here's what I tried. I already mentioned the in-line light on the spark plug wires seemed to look okay. I replaced the plug wires with new ones from O'Rielly. I replaced the plugs with new AC Delco plugs, gapped them properly. This didn't change anything. I replaced the original factory coils with three new BWD Select coils from O'Rielly. If anything, that made it worse. I ran seafoam through the crank case two times and the fuel tank three times.

The oil stays clean, doesn't burn a drop, no smoke at all. The engine runs very strong with the exception of this problem. It runs good cold, but stumbles on itself after it warms up. The only other thing I can think of is that the car did have a new fuel filter installed about three years ago.

Ideas?

Thanks!

David
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Old 07-30-2010, 01:57 PM   #2
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1991 Pontiac 6000 v6 3.1l running rough


I assume this has fuel injectors. Have you been adding fuel injector cleaner to your gas?
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Old 07-30-2010, 02:08 PM   #3
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1991 Pontiac 6000 v6 3.1l running rough


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I assume this has fuel injectors. Have you been adding fuel injector cleaner to your gas?
This car is EFI. Seafoam is supposed to clean the junk out of them. It's cheap enough to try another good cleaner. I'll pick some up today.
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Old 07-31-2010, 12:19 AM   #4
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1991 Pontiac 6000 v6 3.1l running rough


The strongest OTC FI cleaners are Techroline or Gumout with Regane, forget most of the rest of them.
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Old 07-31-2010, 01:15 AM   #5
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1991 Pontiac 6000 v6 3.1l running rough


I would look for either a leaking vacuum line or a leaking EGR valve. Both have parts that operate differently with the engine cold and warmed up. If that has the black plastic vacuum lines, it is possible one has split or the rubber connectors on the ends have simply degraded from age and oil and turned into mush and are leaking.


You can also swing by Autozone and I think Advance Auto (don't know if O'Reillys does it) and have your computer scanned to see if there are any codes present.
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Old 07-31-2010, 03:42 PM   #6
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1991 Pontiac 6000 v6 3.1l running rough


AZ or Oreillys will not be able to scan your car, it is OBD1
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Old 07-31-2010, 04:02 PM   #7
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1991 Pontiac 6000 v6 3.1l running rough


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AZ or Oreillys will not be able to scan your car, it is OBD1
well ain't that a bummer.

OBDI is easy to self scan. It's been long enough I can't remember which 2 terminals to jump to get it to self scan. There should be tons of info on the net about how to do it though.
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Old 07-31-2010, 07:35 PM   #8
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1991 Pontiac 6000 v6 3.1l running rough


my guess is head gaskets. even if you check the oil and it is not milky, they would still be leaking. the next in line would be the catalytic converter. with blown head gaskets, the cat would be done. the 3.1 is really bad for head gaskets. i could think of others, but one thing at a time
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Old 08-02-2010, 10:13 AM   #9
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1991 Pontiac 6000 v6 3.1l running rough


I only had a few minutes over the weekend to look at it. I did put a bottle of Techron in the tank to see if it cleaned anything out. I'll know in a few days if that makes a difference.

I also checked the resistance on the EGR valve, and everything was perfect there. I think the next thing I'm going to do is check for a leak in the EGR valve. It it had a leak, it would produce issues that sound identical to what I'm seeing. I found something online that said to take it off the car and spray carb cleaner in each of the three holes and see if it comes out the other hole. If it does, it isn't closing all the way and is defective. Sounds like the next cheapest thing to check.

If it was a head gasket, would it use or leak oil? It doesn't have any leaks at all, and the oil stays clean all the way through to oil change time. It also doesn't ever move off the full line.

Thanks for the suggestions! I'll let you know what I find.

David
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Old 08-02-2010, 01:13 PM   #10
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1991 Pontiac 6000 v6 3.1l running rough


I had the same motor in my 91 Beretta. Try cleaning the intake with seafoam (sucking through the brake booster). Also check the IAC and EGR. My EGR would carbon up something awful. I also used to take apart the EGR and clean with carb cleaner, and lube the pintals so they moved smoother. You could have whats called the TCC hanging up. One way to test is to unplug the connector to the TCC. This will prevent the "Overdrive" from actuating, and will cause the car to run at a higher RPM at higher speeds, but when it does not disengage when coasting to a stop, will give you the bucking or almost stall condition.
I would try cleaning things first, before disconnecting.
Also check out www.beretta.net, and check out the forums there. Since your car has the same powerplant as the early 90's Beretta's, you will find some good info for repair/troubleshooting.

Good Luck!

TJ

After re-reading your post, you may have some injectors going bad. I did a write up a while ago about testing the injectors. The write up can be found here-http://home.comcast.net/~t.pierro/images/Plenum.pdf

Last edited by TJ_in_IL; 08-02-2010 at 01:44 PM. Reason: additions
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Old 08-02-2010, 04:58 PM   #11
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1991 Pontiac 6000 v6 3.1l running rough


Quote:
Originally Posted by nap View Post
I would look for either a leaking vacuum line or a leaking EGR valve. Both have parts that operate differently with the engine cold and warmed up. If that has the black plastic vacuum lines, it is possible one has split or the rubber connectors on the ends have simply degraded from age and oil and turned into mush and are leaking.


You can also swing by Autozone and I think Advance Auto (don't know if O'Reillys does it) and have your computer scanned to see if there are any codes present.
this and a compression test

a down cylinder and bad egr are two of the more common causes once you check things like plugs, injectors etc. make sure to disconnect the distributor or coil when you do a compression test. it's really easy to waste modern coils when the spark has no where to go
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Old 08-03-2010, 10:01 PM   #12
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1991 Pontiac 6000 v6 3.1l running rough


TJ,

I tore things apart after it cooled down this evening. The IAC sensor was nasty, and the pcv valve moved, but was really sticky. The throttle body had a little bit of gunk in the bottom, and a little bit of sticky oil draining out of it back into the air intake tube.

I pulled the plenum and tested the resistance of each injector. They were 23, 37, 16, 13, 15, and 10 with the engine mostly cooled down. I figured with a range of 10 - 13, with low being bad, what's the deal with the high values on the others? Are the high ones good or bad?

I also pulled the EGR and used some carb cleaner to test it for leaks, and it is sealing 100%.

I went ahead and purchased a new PCV valve and AIC valve and will put those in tomorrow. Oh, and a new PCV hose to replace the one I broke pulling the valve out.

Anyhow, with what I found, there is certainly a few things that could be going wrong. My only question at this point is the injector resistance range being so large. I'm confident in the Fluke meter -- What do you think?

Thanks for the help!

David
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Old 08-04-2010, 02:25 AM   #13
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1991 Pontiac 6000 v6 3.1l running rough


google what resistance should be for your car. it's obd1 which is somewhat universal in that 10-15ohm range. 37 seems excessively high but do check the specs. what's the most odd to me is the spread you have going on.

http://fuelinjectorconnection.com/shop/

can clean and flow your injectors. actually if you call and ask the question you'll probably get an answer. this is the single best injector site i know of online.
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Old 08-04-2010, 01:48 PM   #14
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1991 Pontiac 6000 v6 3.1l running rough


I decided not to mess with it. I called the guy at the injector place and ordered a set. This weekend I'll install those, the new PCV valve and hose, and the IAC valve. I'm going to throw a new fuel filter on it for the sake of the new injectors at the same time.

I'll let you guys know how it turns out.

Thanks!

David
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Old 08-05-2010, 01:30 PM   #15
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1991 Pontiac 6000 v6 3.1l running rough


Please report back, as I am curious.
I have never seen values that high on injectors.
Glad to see there was still some good use for the write up.

TJ
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