1992 3.1 Lumina occasional miss - bucking

[sodak]

I have run out of ideas. I've inherited a '92 Lumina 3.1 82,000 miles. At highway speeds, it drives fine, then jerks like a tramsmission or electrical problem. No Codes, I get steady 12's. Starts good, accelerates good. At idle, after it gets warm, it will miss, surge, and sometimes die. I have good fuel preasure, injectors are all 12-12.1 resistance, I put new plugs and wires in. MAP seems good. Any ideas are welcome. I drove it yesterday 50 mile out and back. The occasional miss is the only thing I can't figure out.

[Schurkey]

Originally Posted by sodak

At idle, after it gets warm, it will miss, surge, and sometimes die. I have good fuel preasure, injectors are all 12-12.1 resistance, I put new plugs and wires in. MAP seems good. Any ideas are welcome. I drove it yesterday 50 mile out and back. The occasional miss is the only thing I can't figure out.

1. I didn't have identical symptoms, but I had similar problems with a '92 3.4L. Lower intake gaskets were toast, allowing an air leak into some cylinders.

2. What is the injector resistance spec? I was thinking it was more like 6 ohms, but I don't know for sure. Maybe I'm wrong.

[Tech II]

I believe it is 12 ohms....

Do a coil output test with a spark tester? Were the coil terminals corroded?

Early 90's, may try a "tap" test on the ECM.....

[sodak]

It's 12 ohms on the injectors. I replaced the plugs and wires, and there was some corrosion at the plug but the coil end looked good. I used a tester on the front 3 plugs (easy to get to) and got spark. I did notice that the spark was inconsistent but wondered if it was normal. The spark in the first two plugs sparked, then seemed to miss a revolution or two, then spareded etc. Is that normal?

[Tech II]

No it isn't....you are going to have to check the rear cylinders too.....

Think you have a coil problem....

[sodak]

OK I'll do that tomorrow. Did the tap test. She started OK, idle was smooth. Tapped the heck out of it, no change. I put a ODB tester on it and got 12's. Then I took it for a quick spin around the block- it was warmed up when I started. It started missing bad backfires, barely made it home. Threw the ODB reader and got all 12's.

I also unplugged the TPS and ran it for a minute no change sputtering and backfiring- mainly trying to throw a code... turned her off read it and got all 12's. Plugged the TPS back in, started it and it continued to run bad.

I'll focus on the coils and make sure I get nice blue spark, no pauses.

Thank You for helping!!!

[Tech II]

Remember, this is OBD I, not OBD II....only OBD II has misfire codes....

[sodak]

OK, had some time, did some testing. I put a spark tester on all of the coil towers using a extra plug wire. I removed one plug at a time and connected the tester. Started the motor and observed the spark. Results... all had spark, the middle coil (3,6) would spark and stop briefly, and spark again. It seemed that the missing was worse during the times where there was no spark. I took the middle coil pack off and tested resistence between the primary towers and got 8kohms, This was true with the two other coil backs too. Can a coil still be bad? I'm tempted to spend $30 and get a coil pack to see, but I also don't want to throw parts at it yet. Ideas?

I also disconnected the TCC solinoid to see if it contributed to the bucking. I took the airbox out on the drivers side and found what I thought was the solinoid (5 wires) disconnected it and drove the car. No change. I also still had overdrive, so I'm guessing it wasn't the TCC solinoid.

[sodak]

Had some time and thought I'd look... nobody have any suggestions?

[Schurkey]

Originally Posted by sodak

Results... all had spark, the middle coil (3,6) would spark and stop briefly, and spark again. It seemed that the missing was worse during the times where there was no spark. I took the middle coil pack off and tested resistence between the primary towers and got 8kohms, This was true with the two other coil backs too. Can a coil still be bad?

Are the coils separate from the module below? Some coils are replaceable, some are a one-piece assembly with the module that isn't serviceable.

If you can get to the underside of the coils, you can check primary resistance instead of secondary resistance. Yes, your coil could still be bad...but it could also be the module. If the other coils spark steady, I'd think the wiring and the crank position sensor are OK.

Originally Posted by sodak

I'm tempted to spend $30 and get a coil pack to see, but I also don't want to throw parts at it yet.

IF you can't get to the underside of the coils...that'd be a good idea. Are you sure the $30 replacement unit is actually good?

Originally Posted by sodak

I also disconnected the TCC solinoid to see if it contributed to the bucking. I took the airbox out on the drivers side and found what I thought was the solinoid (5 wires) disconnected it and drove the car. No change. I also still had overdrive, so I'm guessing it wasn't the TCC solinoid.

Disconnecting the torque converter clutch wouldn't disable fourth (overdrive) gear--but--I'm not sure about the wiring; and why they'd need five wires to control the TCC.

[grog11]

Check the crankshaft position sensor wiring from the modular coil plate to the back sensor location. The wires do fray and ground out to the engine block on the side.
The crank sensor is located way in the back center engine block above the oil pan.The bad crank sensors do cause your symptoms on the 3.1liter engines Remove the front engine dog bone mounts and pull the engine forward for access.

[Schurkey]

Originally Posted by grog11

Check the crankshaft position sensor wiring from the modular coil plate to the back sensor location. The wires do fray and ground out to the engine block on the side.
The crank sensor is located way in the back center engine block above the oil pan.The bad crank sensors do cause your symptoms on the 3.1liter engines Remove the front engine dog bone mounts and pull the engine forward for access.

How does a crank sensor cause misfire from only one coil?

[squekyj]

easier yet take that coil pack and move it to another one then retest see if that pack is still missing if its not missing then its the module , if it does miss then its ur coil pack , also check resistance on those 2 coil wires and check ur plugs on those 2 cylinders .. i have seen plugs crack and make one miss like that cause it cant find a propper ground at the plug all the time, and i my wife has a car with that engine so i know alot of the time u want to ..or lol

[rkvons]

Originally Posted by squekyj

easier yet take that coil pack and move it to another one then retest see if that pack is still missing if its not missing then its the module , if it does miss then its ur coil pack , also check resistance on those 2 coil wires and check ur plugs on those 2 cylinders .. i have seen plugs crack and make one miss like that cause it cant find a propper ground at the plug all the time, and i my wife has a car with that engine so i know alot of the time u want to ..or lol

Yeah, swapping the coil packs is a good idea if it is a specific cylinder misfiring, but make sure the spark plug wires don't move with the coils that are being swapped. They must stay at their current spots.

[sodak]

I'll try swapping the packs in the next couple of days and report back. Sorry for the delay.