Update October 17.
Work has ceased on finding the problem with Scott's 4.9. A little condensed review.
When he bought the car, it was randomly missing on 4 cylinders. No particular thing could be identified as the cause. No bumps in the road, no acceleration or deceleration, no turns. It would just do it, then it would begin running on all 8 again. For a while. Sometimes a short while, sometimes a long while.
Scott, Roger, Raydar, TopNotch, and maybe some others I'm not aware of delved into the car. Every sensor on the engine was replaced to no avail. The distributor was replaced to no avail. One day while still troubleshooting, just by sheer accident, it was found that a fuse block that held among others, two fuses for the fuel injectors had a faulty set of contacts on one of the injector fuses. Move it one way and it would run on all 8. Move it the other way and it would only run on 4.
That problem was resolved by replacing and repinning a new fuse block. But with that problem being solved, another had reared its ugly head. It ran horribly. With lots of input from club members and Pennocks members, just about every theory was explored. ECM. PROM. Grounds. Timing. Timing. Timing again.
The engine would run smoothly with the ALDL jumper in place but would either die or run very roughly as soon as it was removed. So, diagnostics was frequently interrupted to remove the battery, go underneath and replace the serpentine belt when the engine would buck. It was finally determined that the cause of the belt jumping was due to a poorly made idler/tensioner bracket. Several configurations were looked at and considered until finally one was fabricated and that issue was solved.
It was scanned and rescanned. It was analyzed with oscilloscopes. Nothing showed up. Again, timing was looked at. Troubleshooter noted something that he felt was a little odd about the distributor and the cam sensor inside the distributor because when the trigger tab on the bottom of the rotor button plate passed through the sensor, the rotor button wasn't pointing at the #1 wire terminal. He wanted to dissect the old distributor to see just how it worked on this particular engine, but that distributor had been discarded long ago when the new one was installed.
Assuming the spark was breaking down, the ignition coil was replaced with a new one. No change. The cam sensor was replaced with a used one that was in the trunk of the car. No change. Both the coil and cam sensor that was removed were put back into the new distributor.
Yesterday, after attending a local car show, I went to Pull A Part and yanked a distributor from a 93 Deville and delivered it to Troubleshooter so he could analyze it. So, instead of tearing it apart, he swapped it out, pulling the new distributor and putting in the one from the parts yard. Set it according to the factory service manual and fired it up. It ran smoothly with the jumper. It ran smoothly without the jumper.
It could possibly pull a wheelie on the road if the clutch didn't slip. But we kept to the speed limit as we delivered it back to Scott this afternoon. Having replaced the coil and the cam sensor without result, the only thing in the distributor left is the pickup coil and the ICM. One of those was defective right out of the box.
Final diagnosis: Defective Distributor Components.
Thanks to all who contributed to the effort to prevent Scott from utilizing his 45 and propane torch. The tensioner bracket was fabricated by Headhunter1ID, Gabe Anderson.
I would also like to introduce and give a HUGE THANKS to Troubleshooter, better known to all of us as Georgia Fiero's TopNotch, aka Pat Swayne.
