Have a '94 3.9 automatic that's fixing to get shot with a .44. Had the truck for 6 years, it's always had an intermittent no start. Has 141,000 miles on it now, engine is mechanically sound. When it won't start, the ASD times out during cranking indicating no crank signal. Test light at the coil+ comes on briefly then goes out during cranking verifying PCM is opening the ASD relay. A new symptom that appeared last time I drove it is heavy detonation at light throttle in OD. Doesn't rattle in 3rd with less load. {OD off}

What's irritating is it will run for a couple years sometimes without issue then throw a fit. Done this several times, drive it for a year or more, runs perfect. Go out the next day, won't start. Go out a few days later, twist the key and it fires right off. Just did it again a few minutes ago. Wouldn't start a few days back and it's been sitting in the carport, went out to tinker with it tonight and it fired up instantly. Killed it/started it several times tonight without issue. SnapOn scanner showed no codes, and yes on crank and cam sensor signals. It may not do it again for a year or two, or it may not start in the morning. Weather has no affect, hot, cold, wet or dry, nor does a hot or cold engine.

I replaced the rattling timing chain and installed a tensioner a few years ago. Since then I've replaced the crank sensor twice, checked the distributor bushing and replaced the cam sync sensor because it threw a code 54 once, and fixed the gimpy splice next to the relay box. The ground at the firewall is good as well. Eyeballed the flex plate through the crank sensor hole looking cracks or rubbed spots, found nothing. I've pulled and wiggled on the harness and connectors both when it won't start and when it's running to no avail. Also kinetic tested the PCM during both conditions. {whacked it with my fist while calling it choice words}


Any ideas on the intermittent crank signal? .44 rounds ain't cheap, but I'm about to the point of spending a few bucks.

 

What brand crank sensor? These trucks really don't care for some of the aftermarket fellers.

 

Hecho En China Standard Motor Products. They act the same as the original, which may mean nothing in particular. Could still be the sensor. When I changed out the original, it ran about 2 weeks and quit again, then of course, it decided to start and run OK. Out of spite I pulled the new sensor and it had lightly rubbed the starter ring, so I thought well maybe. Got another Standard brand, bent the mounting tabs ever so slightly and installed it. Ran the motor for a bit, pulled it again and made sure it wasn't rubbing. Ran perfect a couple weeks, then wouldn't start. Didn't even raise the hood, just went back in the house. An hour later it started instantly and ran for close to three years I guess with no issues......until about a month ago. Starts and runs now, may not throw a fit for another 2-3 years, who the hell knows?

 

Man what a trip. Sounds D's like u gotta Dak version of that damn creepy haunted car, whTs the name, Carrie or Christine. Something like that. I will say that there's more than just one splice in the harness. I just completely stripped And rebuilt my harness

 

This is just a thought, but the manual and automatic use two different sensors. By it hitting, I wonder if you have the wrong one.

 

no, one wont plug into the other one harness plugs are mirror images of each other

 

I'd say go through the harness and check all the splices. Especially on the wires that send power to the pcm, it sounds like it's just intermittent power loss somewhere. Going through the harness is a good project for the long run anyway

 

Still fired up this morning, no issues. Had already bought another crank sensor a month or so ago, so I changed it again just out of spite. Also disassembled the harness side connector to look for issues, found zilch. Went and put gas in it, drove it to town and ran it through the car wash, ate lunch, back home. About 30 miles. Started every time, ran like a champ. Piece of crap.

If I had the cash I'd stick a mechanical 4BT in it, that'd cure it's computerized intermittent BS for good. Might actually be able to pull something with it too.

 

When I pulled apart the harness on my 93 there was a total of 15 to 20 splices throughout both the injector harness and the pdc harness. I didn't want to take any chances so I completely rebuilt each splice using fresh wire where needed, fresh solder, and self sealing heat shrink. I didn't want to take any chances. It was a 3 day project to get it pulled out, tore down, cleaned, fixed, re taped, and re I stalled. But I do know that there is no more electrical Gremlins that I'm gonna have e to deal with.