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Misfire unless key in "start" position

I have a 2001 Dodge with the 350 in it. I have about 90k on it, and its in relatively good shape. But I have an issue that I just can’t figure out. In the fall winter or spring, no issues - in the summer, when the outside temperature is over 70 (or it can be lower, if I’m going slowly down back roads) I get a misfire, after the engine is hot. It will idle fine, or maybe slightly low. But when I put it in drive, and the engine is under load, it starts to misfire badly. HOWEVER, I can get it to stop misfiring, if I turn the key to the start position. Yesterday I was driving while it was very warm out, it started to misfire slightly as we were climnbing a grade, so I turned they key to start, and drove up the hill fine - when I let the key back to the run position, the misfire was getting worse.

Here’s some other possibly related info:

  • the check engine light is always on, with a code that has something to do with evap. I forget exactly. No other code is stored in the computer. Nothing. When its misfiring, the CE light is either flashing (assuming due to raw gas hitting the cat?) or it goes out, and stays out until the next time I shut off and start my truck.
  • the tach fails when its misfiring, but all other guages are fine
  • when I turn the key to the start position, the engine runs fine, but I lose all dash electronics, except my tach. (I think this is normal, but I’ve fiddled with this for so long, I forget whats “normal”)
  • engine temp never goes above approximately 190 on the dash guage, and at idle I think it was around 200 when checked on the code scanner.
  • There is a slight exhaust leak, and if I remember right, its before the cat.
  • if I pull over, and let the truck cool down, or turn the heat on full, it seems to help.
  • sometimes, when the truck is idling next to my wifes non-running car, the headlights on my wifes car will flash dimmly. Not like the alarm is going off, full power flashing, but as if current from my truck is reaching her car and surging her system. (possibly unrelated I guess, but I’m so baffled, I have to include it)

Things I’ve changed:

  • crank angle sensor
  • cam angle sensor
  • when it was misfiring, we took the computer out, and put it in another identical truck, which had no issues with the computer from my truck
  • I changed an o2 sensor, but unfortunatly, can’t remember what one. I believe it was the front 02…
  • the very first thing I replaced, a couple summers ago, was the distributor.

What am I missing? I’m thinking about changing the ignition, but it seems odd that anything on the cab side of the firewall would be affected by temp nearly as much as something in the engine bay.

Pete