No spark from cylinders 2 and 5?

BASS903

MEMBER
1988 OLDSMOBILE 88
3.8L
V6
AUTOMATIC
122,587 MILES

I just bought this car and after a few miles of driving it misfires and I have found cylinders 2 and 5 have no spark coming out of the coil pack. I determined this by pulling the plug wire.
I tested the coil pack for continuity and have matching numbers on a cold engine verses the hot condition once the problem occurs. So, I do believe the coil pack itself is good.
I can't find out how to check the ignition control module or wire to and from the cam and crank sensors.
I don't want to buy an ignition module or fire the parts cannon at this thing.

I am a certified diesel technician and do know my way around.
Please any troubleshooting help would be appreciated.

5 Replies

STEVE W.

MECHANIC
13,452 POSTS

Okay, the coils are a common failure item as is the ignition module itself on those. They are a waste spark system so each coil fires a pair of cylinders. In this case 2 and 5 fire together. The fastest way to test if it's the coil or the module is to swap the coils. Pull the wires off the 2 and 5 coil, remove the screws and pull the coil off. Repeat for the 1 and 4 coil. Put the 1 and 4 coil in the 2 and 5 location and the 2 and 5 in the 1 and 4. Connect the plug wires back up. Start the engine, misfire is now on one and four, the coil is bad. Misfire stays on two and five, the module is bad. The other sensors do nothing but tell it cylinder position, if they work for one cylinder, they work for all. It's common for the coil connections to the base plate to corrode but far more common is for the coils to fail internally. FYI, I like to use only OE coils, I have had bad experiences with many aftermarket units. Same with the ignition module.

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Sunday, June 23rd, 2024 AT 4:32 PM

BASS903

MEMBER
5 POSTS

Thank you. That worked.

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Tuesday, July 9th, 2024 AT 12:13 PM

KEN L

MASTER CERTIFIED MECHANIC
47,573 POSTS

STEVE W. Is one of our best! Thanks for letting us know, we are here to help, please use 2CarPros anytime.

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Tuesday, July 9th, 2024 AT 12:14 PM

BASS903

MEMBER
5 POSTS

Now I have a different issue. My son drove and parked the car at a store. It ran fine. He came out and it wouldn't start. It cranks, backfires, tries to start but won't. I replaced the fuel filter because it had a clogged filter right before I bought the car, so I thought it may be the issue. It took a few minutes of cranking, but it started to run then quite after about two minutes.
When cranking it backfires some. I put the old ignition mod back on, still no start. In the process of switching the ignition mods, I forgot to plug it in. The engine cranked over fine, no back fire.

I have fuel pressure, but no gauge to check it.
I have spark on all six coil outputs.

I have not checked the wiring to the cam or crank sensors yet, or any relays or fuses.

It sounds to me it's out of time, but ran fine the two minutes it started. Some other posts mentioned that the crank sensors is a known cause.

No engine codes other than 12.
I'm going out to see if I can rig a gauge up and check some wiring on stuff on the heat index drops a little out side.

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Tuesday, July 9th, 2024 AT 1:00 PM

KEN L

MASTER CERTIFIED MECHANIC
47,573 POSTS

Sorry, we only handle one problem per thread, please post your new question here, you must be logged in.

https://www.2carpros.com/questions/new

Cheers, Ken