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So i have a 1986 L98. Ive changed the entire ignition system, including plugs, wires, cap, rotor, distributor unit, esc module. Ive done a compression test which checked out fine, ive replaced all the injectors, ive changed all the intake gaskets and insured there arnt any vacuum leaks. Drivers side manifold gets warmer faster than the passengers side but they both end up the same temp. Maf sensor has been replaced, tps has been replaced, all relays have been replaced. all ignition has been checked with that cable that you put between the spark plug and the plug wires that sparks everytime the cylinder fires. I'm out of things to do. All temp sensors have been changed as well, and ecm has been replaced. Any Ideas?
If the miss-fire is consistent, can you identify which cylinder is miss-firing by pulling plug wires? Are you sure that its not a lean miss caused by an injector not working (that could be a wiring or connector issue and not a bad injector)? Like the patina!
Plugs are all firing, i think im going to pull the power from injectors 1 by 1 and see what happens. Thanks for the input! ill update tomorrow afternoon
could be a wore out cam lobe or a bad valve? Like the wheels.
Car only has 30k original miles so im looking more at an electrical problem. It has run perfect before, it just randomly decides to run like crap all the time now. Sometimes i can still get it to run well but very seldom
Plugs are all firing, i think im going to pull the power from injectors 1 by 1 and see what happens. Thanks for the input! ill update tomorrow afternoon
The reason I suggested pulling plug wires was not to see if plugs worked... I believed you when you said they were good. If you pull plug wires on a consistent miss, the engine will run worse on every cylinder except the one already missing. If running on seven cylinders and you pull the bad one it should cause very little change. Any other plug wire will have you running on six cylinders.
My bet is that an injector isn't getting consistent power. Pulling the plug wires to identify the bad cylinder is going to be easier than the injector connectors I think.
had that issue once on a different vehicle. turned out to be one of the injector wires bad in the harness. do what was suggested above, do the same with the injector connectors, and/or get noid lights.
I would also pull the plugs. are the ones misfiring wet? did you get a bad plug? yes, it happens...cracked on install, etc.
I like the idea of pulling the plugs off the injectors 1 by 1 as it's likely not the plugs or plug wires by 86's description. Plus that won't foul the cats if they are still there.
I like the idea of pulling the plugs off the injectors 1 by 1 as it's likely not the plugs or plug wires by 86's description. Plus that won't foul the cats if they are still there.
Either way will shut down the cylinder. If it is the bad one there will be no change in the engine missing. If its a good cylinder the engine will run worse. All we are trying to accomplish is to find the bad one. I am also pretty sure its an injector wiring issue, not spark but... which injector?
I have had the same problem quite a few years ago, replaced maf, ecm,burn off module, esc sensor, knock sensor, injectors ignition module leads plugs ect. Had spark to all plugs and there were 12 volt pulses to the injector connectors no fault codes i was stumped.
I woke one night and had a brain wave, i went out at 2 am and started the car from stone cold. Ran it for 10 or 20 seconds and turned it off.
Checked the exhaust an inch from the heads, found cylinder #4 cold.
Swapped the injector harness from #2 and found the fault had gone to cyl #2. i was pretty damn happy as the car had sat for around 6 months and i have found the problem.
When the injector connector was flipped over it showed 12 volt pulses, the metal strip inside the connector had broken and would connect when flipped over for testing but would not operate the injector.
I replaced the injector connector the next day and she was fixed, i was very very happy to have found the problem.
We tend to tug at the wires to remove the connector from injector that can damage them.
So start the car when it is cold run it for 10 or 20 seconds and look for a cold exhaust header/manifold pipe, then you know what cylinder is affected.
The injectors are batch fired so you have no problem swapping the harness between one injector of the one near it.
Check the EGR exhaust gas recirculation valve closes.
Good luck
Last edited by gerardvg; Apr 23, 2015 at 12:35 AM.
I have had the same problem quite a few years ago, replaced maf, ecm,burn off module, esc sensor, knock sensor, injectors ignition module leads plugs ect. Had spark to all plugs and there were 12 volt pulses to the injector connectors no fault codes i was stumped.
I woke one night and had a brain wave, i went out at 2 am and started the car from stone cold. Ran it for 10 or 20 seconds and turned it off.
Checked the exhaust an inch from the heads, found cylinder #4 cold.
Swapped the injector harness from #2 and found the fault had gone to cyl #2. i was pretty damn happy as the car had sat for around 6 months and i have found the problem.
When the injector connector was flipped over it showed 12 volt pulses, the metal strip inside the connector had broken and would connect when flipped over for testing but would not operate the injector.
I replaced the injector connector the next day and she was fixed, i was very very happy to have found the problem.
We tend to tug at the wires to remove the connector from injector that can damage them.
So start the car when it is cold run it for 10 or 20 seconds and look for a cold exhaust header/manifold pipe, then you know what cylinder is affected.
The injectors are batch fired so you have no problem swapping the harness between one injector of the one near it.
Check the EGR exhaust gas recirculation valve closes.
Good luck
Great idea. That should work and has a good chance of being the issue. But what happened to the OP?
So, come to find out after all the work I've put into the car, it was a blown fuse. I changed all the fuses multiple times with new ones but the fuse for the passenger side injectors was blown so they weren't firing on that side of the engine. I unplugged injectors one by one and found that the passengers side ones didn't change the idle speed when I unplugged them. Changed the fuse and it runs beautiful... I feel like an idiot now 😅😅😅
So, come to find out after all the work I've put into the car, it was a blown fuse. I changed all the fuses multiple times with new ones but the fuse for the passenger side injectors was blown so they weren't firing on that side of the engine. I unplugged injectors one by one and found that the passengers side ones didn't change the idle speed when I unplugged them. Changed the fuse and it runs beautiful... I feel like an idiot now 😅😅😅
Consistent Misfire 1986
If you pull plug wires on a consistent miss, the engine will run worse on every cylinder except the one already missing. If running on seven cylinders and you pull the bad one it should cause very little change. Any other plug wire will have you running on six cylinders. 
Great idea. That should work and has a good chance of being the issue. But what happened to the OP?
