When this happens - if you shut the truck off and then re-start it, doesthe miss go away after the re-start or does it continue until it runs for a period of time ? How long does it have to run before it straightens out ? Assuming it doesn't cancel after the first time you start it andstill is missing on a restart : try switching wires for cyls. #5 and #7 before starting it a second time and see if the miss travels to cyl. #7. Just curious.

 

Ignition is controlled by the crank sensor.The sensor recieves it signal from'windows' in the flexplate. The sensor is obviously good or you would get a code and the problem would move around. If the flexplate were cracked by the #5 'window' it could possibly build up some kind of charge that would affect the signal. Just a guess.

My only other thought was the ignition driver in the pcm.

Wires are easy enough to check. #5 and #7 are practically the same length. Swap them just for ****s and giggles, but if they are new and the problem has recurred through more than one set, I doubt that's it. You said you had replaced "caps" and you know it isn't the button.The problem would move around with a bad coil, distributor etc. O2 sensor or cat is not going to drop the spark to ONE and only one cylinder consistentlyand the truck "runs like a champ" otherwise.

When you say you have confirmed this, have you tried quickly clamping another wire to see if you are getting spark? Could it be a inductive coil issue with the timing light?

If you figure it out please let us know.

 

Appreciate all the help guys. Here are some answers to your questions. I never get the multicylinder misfire code. Currently, it is on its third cat coverter. However, I doubt this would be the problem since I have been living with the issue for over a year. When the othercatswent, it was obvious and besides, it is only one cylinder and always that cylinder. Turning it off and starting back up does not help. The mis is still there. It could clear up in 5 seconds or take as long as 30. Timing light is working, I use it on my 67 pontiac without issues, but I can verifiy it's operation as you have asked mopowar. I doubt the wires are the issue. They have been swapped, changed, cussed at and threatened without success.

 

Forgot to add. I have found that if you let it idle until the mis quits, it will not generate a code in the PCM. If you try to drive away and let the RPM's get up a bit, it will drop the code if it is missing. I have started to let it sit a bit when I notice the miss before driving.

If its the flex plate, I will just have to keep on living with it.

 

Have beenunable to try the injector swap ro check the compression as of yet. Work has had me hopping and I am just now getting back to checking the forum. Verified the operation of the timing light. Tried to insulate the wire, no help. Mis actually went away for a day, but came back.

 

I know that this is an old post but I have still been working on this problem and I think that I have found it. The truck continued to have the same problems but when winter came, they went away. The spring came, and every time it would rain it wold miss for a long time on #5 cylinder when started. It was always in the morning and then it started if the truck set for a couple of hours in the rain. I pulled the plugs off of the controller that is mounted on the fire wall and cleaned them all with plastic safe contact cleaner, both the plugs and the terminals on the control box. When I first started it up it ran like crap. Wiggled the plugs and the truck has run fine since with no issues and through 3 rain storms since. Thought this might help someone that is fighting something similar