Join Date: Mar 2008
Location: Deerfield or Sanford, wherever the weather's nicer
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Intermittent Misfire / Start Failure
I'll try to keep this short, yet complete (not all that easy).
1. My '95 F250 7.3 occasionally misfires when accelerating gently from a stop or slow coasting. It feels like just one or two misfires, after which it runs normally. This occurs an average of maybe once per month (sometimes 2-3 times in a day; sometimes not for a few months). It has occurred since I bought the truck in 2000 with 75K miles on it. It now has 204K.
2. A couple of months ago, when starting the truck, the "Wait to Start" light didn't come on, and it wouldn't fire. Only after turning the ignition off and on again did the "Wait to Start" light come on. After it extinguished, the truck started and ran fine. This has happened 4-5 times since then.
3. New today (2013.06.28): on a 40-mile round trip, the engine cut out three times. There was no response from the accelerator for a few seconds, but the engine was still turning (I didn't lose power steering), so it was either idling or being turned over by the force from the rear wheels through the transmission. After a couple of seconds (with no intervention from me), the engine resumed running normally. In one instance, the "Wait to Start" light came on for a second, maybe less.
1. At 127K miles, it began running horribly, and I replaced the cam angle sensor. That fixed the really bad behavior, but didn't affect the occasional misfire.
2. At 180K miles, I replaced the stop / tail / turn lamps, hi-mount brake lamp, and front parking / turn lamps with LEDs and the flasher with an electronic unit (no load resistors). I noticed (after much frustration) that the hi-mount brake light was dimly illuminated when the truck was running, that the transmission wouldn't lock up in overdrive, and the cruise control wouldn't engage. The cause was reverse-leakage from the engine control unit. Without the incandescent lamp load, the back-voltage rose high enough to give the indication that the brake was being applied. I installed a relay that clamped the brake light line to ground when the brake was off, which solved the problem. But it seems like that's a lot of reverse leakage. Could this be indicative of a failing "chip"?
Some or all of this stuff could be related, or they could all be independent, exasperating issues. Any thoughts from the community would be really welcome.
Last edited by John Miller; 06-28-2013 at 10:58 AM.
Reason: A third symptom