Plagued By a Misfire

For several weeks, I have been plagued by an engine misfire in my 2002 Jeep Grand Cherokee Laredo (affectionately named The Heep). These problems are to be expected with any vehicle of legal drinking age and over 346,000 miles, but this one has really thrown me for a loop. To be clear, this is a “dead” misfire, which means that cylinder never fires. I’m only running on 5 of 6 cylinders. And that’s bad.

The Good News: I may be close to putting it to bed.

The Bad News: The saga is real…

1. I found a fouled plug, so I replaced all six. Still misfiring.
2. I suspected a bad ignition coil rail, so I replace that. Still misfiring.
3. I had replaced the fuel injectors some time ago with aftermarket 4-port units. I still had the originals in the garage, so I put them back on. Dead misfire is gone, but there’s a slight occasional misfire or irregularity to the engine. This is likely the driving reason I changed the injectors in the first place. At least the truck is usable.
4. I shipped the aftermarket injectors back to the warehouse to be tested and rebuilt. The company found one bad and replaced it, then rebuilt the rest. They were returned to me this week.
5. I swapped out the injectors (originals for the rebuilt aftermarket units). DEAD MISFIRE IS BACK! 🤬
6. Pulled the fuel rail and had my son turn the engine over. One of the injectors is hold no back pressure, allowing gasoline to freely flow into the cylinder.

Monday, I will likely ship the known-defective injector back to the warehouse and have it rebuilt or replaced again. The Heep will ride again, but I’m likely out of a truck for another week.