91 Lumina 3.1 Missing / Running Rough

[mdelorie]

As the title says, the 3.1 seems to be running terribly rough.

The vehicle hasn't been driven much in the past two years, probably only had 3000 or 4000 kms put on it since October 2007.

A couple weekends ago I took it for a fairly long trip - 800+ kms over two days - it seemed to run alright, the odd barely perceptible miss here and there.

Tonight, I took the car out to see a movie. I was driving fairly fast on the highway, and it seemed to be running alright... as I slowed down, however, it started to miss / run rough more and more. Parked at the theatre, watched the movie, came back out and it started fine, but runs rough even at idle.

I limped it home with varying levels of rough running. We'd go around a corner and it would seem to run alright for a few seconds, then back to rough. It seems to run worse at low throttle settings / RPM. Condition is the same regardless of gear selection - even does it in neutral. There doesn't seem to be any regular pattern to the missing to indicate a single cylinder being at fault. The check engine light is not lit. I do have an OBD 1 cable and some assorted software available for pulling data from the PCM.

I haven't started any hard troubleshooting yet - I just wanted to pass it through here to see if anyone has any ideas. Corroded spark plug cable connection? Bad DIC module? Fuel injector? Fuel pump?

Any advice or suggestions on how to troubleshoot it would be appreciated.

Thanks!

[RedogOnyx]

Bad plugs?

[mdelorie]

Am I chasing the right path thinking it's fuel / spark related? When I started the car for the first time this year, there was a fair amount of ticking, presumably from the lifters. Is it possible / common for a lifter to collapse? I can't remember if they're hydraulic or solid on that engine. Would a lifter cause the symptoms I'm describing?

[WrathOfSocrus]

Due to the intermittent nature I would check the spark plug wires first. Insulation damage may or may not be easily visible. Spark plug wires and exhaust manifolds don't play together well. Not too long ago I encountered a truck with a miss and ticking sound. The ticking was caused by the spark jumping from the wire to the exhaust manifold. Sounds bizarre but by simply replacing the wire with one laying around from an old set and routing it around the exhaust manifold cured the problem.

A trick I learned for finding spark plug wire problems is to open your hood in the dark. If you see any sort of light or sparks then there is the problem. Being intermittent I would guess it is fuel, spark, electrical related.

[LeftVentricle]

^^^^ Going with this post, I'd definitely recommend doing a tune-up (plugs, wires, air filter), oil change and a fuel filter, and get some good gas in the tank along with some injector cleaner. If it doesn't clear up after that, you might have something a little more expensive going on:

-The MFI engines have a tendency to eat fuel injectors after a while. And due to the nature of their firing (they run on a common circuit), one bad injector can take out the other two on the bank. I say expensive because they're around $70 US new from, say, Autozone, and it's adviseable to replace them all. One bad apple, etc. Plus, if you farm it out, as an example, at a dealership GM bills 5.2 hours of labor whether you're replacing one or six.

-A little bit more of a long shot is the ignition coils and/or ignition control module. Same as with the fuel injectors, you're dumb if you don't do all three coil packs at the same time along with the ICM. Again, expensive; I spent over $200. Not only that, but the location of the ICM and coils is absolutely retarded on the MFI engines: directly below the front exhaust manifold. I wrecked my knees and back kneeling bent over the front of the car replacing mine. Total pain in the ass. Can't imagine having to do this in a J-body...

-Less probable is the crank position sensor, but that was less of a rough running problem, more a dies-while-driving-and-won't-restart-until-fifteen-minutes-later problem. I did a write-up on replacing the crank sensor here. Part is cheap in comparision, around $25.

Small note on all of the above: You probably won't have a check engine light for any of this. At least I didn't.

-Last but not least is the knock sensor. This will set a code 43 as soon as the engine reaches operating temperature. Symptoms will be a loss of power and fuel economy and a rough, low idle. The part is around $50 and is quite close to the crank sensor, so the procedure is nearly identical, except that the sensor goes in and out with the help of a 22mm socket.

[SofaKingWeToddDid]

i would put new tires and a brand new windshield on it. and $4,393 worth of stereo equipment. pound bass till you cant hear the motor, problem solved.

[mdelorie]

I know this is pulling from the dregs of time, but I'm honestly just now getting around to troubleshooting this problem. Replaced the battery, used a spare spark plug to verify spark from all six ignition coils, and completed one cylinder of a compression test with a result of 180 psi. Problem remains. I'm leaning towards fuel system, either pump, injectors, filter, etc. but I want to check everything else to be exactly sure.

As I go through, I'll be measuring resistance on all the spark plug wires, and gapping / cleaning the spark plugs. Couple questions / clarifications:

Spark plug wires - 7000 - 9000 ohms per foot a reasonable figure to use? I can't find it written down easily anywhere like that, but I seem to remember that figure from somewhere.
Haynes manual says .045" spark plug gap - confirmed?
Normal compression figures for the engine.
How might I go about testing the injectors? I have a Fluke 88V multimeter which has all kinds of great duty cycle measurements, etc, available, if anyone knows how to do that...
How might I go about testing the fuel pump - would I need a pressure of some sort?

Thanks in advance everyone,

[mdelorie]

Bump

Anyone?

[86FieroSEv6]

Have you pulled your EGR valve and made sure it isn't stuck open? The fact that the symptom popped up after a long highway run then decel' is what got my attention. EGR sticking open is common on GM due to carbon buildup.

[mdelorie]

Well, two years of neglect later, I finally got a chance to sort the problem out. Of all the stupid things, it ended up being a plug with a broken ceramic insulator on the portion of the plug that's inside the engine. $3.20 part. I had replaced a coil and an EGR valve in the process.

Learn from my mistake - check the damn plugs first!

[Schmieder]

Well, two years of neglect later, I finally got a chance to sort the problem out. Of all the stupid things, it ended up being a plug with a broken ceramic insulator on the portion of the plug that's inside the engine. $3.20 part. I had replaced a coil and an EGR valve in the process.

Learn from my mistake - check the damn plugs first!

Yup, My second WOT test run in my turbo project melted the ceramic bond to the plug. The ceramic fell down and insulated the terminals. It was running really rough, just enough to get home. I feared a melted piston.....thank god it was a melted plug.....lol