BACKGROUND: At the end of June on the way back from Kettle Falls, WA the bus started bucking/misfiring. I was able to limp home and did some diagnosing once there. The problem seemed to be a hot coil issue. The engine would run fine while cool, then buck once hot. I swapped in my spare coil and the issue seemed to go away. This past weekend while on the way to Cle Elum, WA the problem reemerged. Again, I was able to limp home, but the problem was no longer confined to when the engine was hot. I swapped back to the original coil and was able to get too and from work on Mon, Tues, and Wed. On Sunday, I had ordered a pair of Brazilian Bosch Blue coils. They arrived tonight, but this morning the bus wouldn't start at all. I swapped in a new coil, but no luck on the start.
SYMPTOMS: The engine turns over just fine and will seem to catch just once, but once I release the key, it dies. After that, it won't even catch. If I let it rest for a while, I'll get the catch-once behavior again, but still won't run.
DIAGNOSTICS SO FAR:
- I swapped in my spare, known to be good, double relay. No effect
- I checked the wiring at the starter, ignition switch, headlight switch, and hazard switch for loose wires or connectors. All looked good.
- I checked the various vacuum hoses for anything loose or blown off by misfires. Nothing out of place.
- I checked the distributor to see if the timing clamp was loose. Nope.
- I pulled the air cleaner assembly and checked to see if the flap in the AFM was wedged in the open position. Nope.
- I pulled the cable going into the AFM as it sometimes works loose. Looking at the connector, pin 6 of 7 was recessed a bit. I tried to pull it back into place, but couldn't get it properly seated. No change.
- I confirmed spark at each of the ends of the spark plug cables. All looked good.
- I verified the fuel pump worked when operated at the AFM.
- The fuel pressure maintains 28 psi and jumps to 38 psi while cranking.
- I verified the FI grounds were connected.