Hello all, have been struggling with this problem for over a year. My Expy starts and idles normally.After driving for 15-20 minutes, and only very intermittently, it will either "hiccup" and keep going; or in the worse case will go nuts ,tach revs up and down,theft light blinks etc,and die.It will always restart and go along it's merry way, though occasionally I'll have to wait several minutes.All this without throwing any codes. Ford dealer put in a new fuel pump and reflashed the PCM last Oct,and the problems only just re surfaced this week, which by coincidence was the first warm days since the re-flash.Before that I cleaned the MAF and I didn't detect any vacuum leaks.

My gut tells me there's some sort of electrical problem here but would appreciate any help/advice .Thanks in advance

 

Sounds like an intermittent interruption in the power feed to the PCM.

About the only thing I can suggest at this point is to replace both the PCM POWER and the FUEL PUMP relays.

Since it's extremely intermittent and doesn't give much in the way diagnostic symptoms, about the best best choice would be to start there.

Steve

 

Sorry to take so long to report back.Due to a family members hospitalization , I could not swap the relays until Wednesday night.As a precaution, I removed the neg bat cable and changed both fuel pump and PCM relays.After nearly 200 miles and one fill-up no problems to report.I'll try to update in a week or so. Thanks again for the suggestion.

 

Well, things looked good for 1 week until last night when my wife informed me of a stall while she was driving. No MIL,full tank of gas, engine doesn't even completely die, it's kinda like a "hiccup".
I'm starting to worry it's the PCM. Any other suggestions would be greatly appreciated.

 

While it is a possibility, I really don't expect the PCM is at fault. The odds are that there is an intermittent wiring harness connection somewhere.

You are now in a race to get lucky and find it before your wife loses her patience with the truck (and you) and gets rid of at least one of you.

Inspect your exhaust manifolds and down pipes to see if any wire harnesses may be intermittently touching. Same for the driveline, if 4WD.

Barring that, I'd suggest that vehicle harnesses be inspected carefully. Start with both fuse panels. Pull them out and inspect the connector pins for corrosion, bent, pushed, or otherwise damaged pins. Clean with contact cleaner and reinstall with dielectric grease. Remove each fuse, one at a time, and inspect the contacts for any spreading or other defect.

Do that also for the PCM connector, the ignition switch harness, and the harness that goes back to the fuel pump.

If the wife has a large and heavy key chain, perhaps a worn-out ignition cylinder might be the problem.

I'd also inspect every ground connection under the hood and behind each of the kick panels.

Good luck, intermittents are the cruelest hoax on both owners and technicians.

Steve