Intermittent engine stumble if car sits for long in humidity.

[turbows6]

I hate to post another troubleshooting question, but here goes.

My TTA will intermittently run rough if it sits for several weeks. I've dealt with this issue for a couple years. All of my garage spaces are full and the car has been parked outside for several weeks without being driven (and it's been rainy a lot this year). I recently started it up to drive it, and the "stumble" is back. Before parking it, I had been daily driving the car 60-70 miles a day and the car ran perfectly.

In the past I've fixed it by changing plugs. Most of the time that fixes it, but there is no reason I can think of that the plugs would foul just from setting for a few weeks.

This time I Ohmed the coils and wires, all of that looked good. I used Deoxit on the plugs, coil, wires, ignition module harness, injectors, injector harness. That made the problem disappear almost entirely. I actually thought it was "right", but it is still occasionally bucking/running rough.

The weird thing is that it typically seems to clear up and run smoother if you roll into the throttle. It seems very random, but not an issue that makes the car undriveable or triggers any malfunction codes.

The common denominators seem to be humidity, not being driven, and/or a few thousand miles on the spark plugs.

Has anyone else had this issue before?

 

[Buick Mark]

If I remember correctly, there was an issue with a couple terminals on the coil pack getting wet/damp. Are the wires original? If so, I'd replace 'em, even if they ohmed out ok, the insulation may be compromised from age and heat.

 

[TurboBuRick]

The infamous cam sensor syndrome. Start the car, unplug the cam sensor, go for a ride.

 

[turbows6]

I drove the car back from work last night, and it started and drove fine. It's a 30+ mile drive home, and the misfire got worse as I drove it home. It was running like crap by the time I got to the house, but still able to idle. It acts like an ignition module, but the module is only a couple years old. I took the coil off and it doesn't show any visual signs of heat damage (it's not bubbled up or melted etc. all the connectors look clean)

Unplugged the cam sensor and that made it run worse in batch fire mode.

I've cleaned virtually every connector on the motor and at the ECM with Deoxit.

Put new plugs and wires on the car. The misfire was still there.

I put a timing light on each of the plug wires and they were all firing.

Engine isn't making any "weird" noises, and it's got a roller cam.

Car isn't smoking out of the exhaust or smelling overly rich.

I guess I'll try getting a set of noid lights and seeing if the injectors are getting a proper signal. (I guess I could try pulling the connectors individually and if pulling one of them has no apparent effect on the engine running it's probably an issue with that injector)

Fuel pressure is normal, no codes on the scanmaster. Engine cranks over good, so I don't think it's a grounding issue. I've put redundant grounds on the Ignition Module.

 

[TurboBuRick]

Sounds like the module is bad if it won't run in batch fire. What brand is it?

 

[turbows6]

Module is an O'reilly's (who knows where it came from lol), so it's entirely possible that the module is junk just simply because it's from O'reilly's even if it's fairly new.

I've run 2 half-tanks of gas through the car since starting to drive it, so I don't think it's bad gasoline, and the problem seems to be getting progressively worse.

I don't know if this makes sense, but it just sounds like an old beat up farm truck while it's running. It idles and revs, but sounds sluggish and doesn't rev cleanly, but like I said, it's intermittent, but becoming more prevalent. Going down the road you can hear it run clean as a whistle, and then sounds like crap, back-and-forth in an almost random digital nature if that makes sense. Whatever the issue is, it's ON/OFF in nature.

 

[turbows6]

BTW, the cam sensor has the RJC repair kit installed (has had that for a few years, and I see no visual problems with the cam position sensor under the cap)

Have a new CCCI module on the way, I guess I'll know if that the issue when I put that on there. I have questioned weather the ECU is faulty, it says it was remanufactured by GM on the ECU. I just can't recall virtually anybody having "issues" and it actually turned out to be the computer. I need to install the Powerlogger software on my new laptop and datalog. Maybe that will give me a hint.

I just think it's weird because the car was running and driving totally fine (although this issue has been apparent in the past at time, but seemed to go away for no reason I could figure out, or changing the plugs would fix it)

 

[earlbrown]

If you're going to troubleshoot using the 'unplug the cam sensor' method, you have to unplug it when it's running right.

When the ECM loses contact with the cam sensor it goes by the last thing it heard. If you unplug it while the sensor's flaking out, it'll use a bad signal as it's reference point.

Not saying you do or don't have a bad cam sensor, but that test shouldn't be used a given.

 

[turbows6]

I think I've found the issue. Unplugged each injector individually, and all of them made the engine run rougher, except for cylinder #6. I connected the wires back to cylinder number 6 and jiggled the wires and the motor cleaned up, and a little whisp of smoke burned of the exterior of the #6 header primary tube (indicating to me that the cylinder hadn't been firing, but started. I think there must have been some crud on the header from changing plugs and wires last night. ) I'm crossing my fingers, but I believe there is a bad/weak connection to that injector.