Ignition Cutout while driving.

[Slysdexia]

Ignition Cutout while driving (Bad PCM?).

Alright, I've got a '94 ranger with the 4.0 OHV, 5 speed, it's relatively solid, but we're hunting a misfire, and have replaced the FPR with no changes, it'll do it with the MAF plugged in, but won't without, and I picked up a new MAF, it didn't change anything, so I returned it. New Fuel Filter as well.

Anyway, on to the issue at hand. I was on some back roads one morning, avoiding freeway traffic, when I come across a deserted stop sign, so when I leave the stop sign, I give it some right foot, just for kicks, really, and I hit 3500-400RPM in 2nd gear, and the ignition just shuts right off, radio keeps going, gauges all flatline, like I'd shut it off, I let off the gas and it instantly comes back, MIL not on, no idiot lights, nothing. Happened again last night, coming off a stoplight, I'm not even goosing it, and 2000RPM in 2nd gear it does it again (at this point a mechanic has looked at it but can't figure it out without replacing parts, his guess if ford programming, but we know it reacts to throttle input) so I immediately let off the throttle, and it's back up like nothing happened, I end up catching the next light, and I come off the light like the bed is full of fine china, and at 1900 RPM in 2nd gear, it tries to do it again, but I caught it before it did anything more than blip.

This is a frustrating and possibly dangerous issue, and I've got to drive 300+ miles per week. This truck has obviously been victim to some hoonery, judging from the muddy water and sand in the radiator, muddy water in the PS lines (all better now). So we can assume the ECU has been submerged, and that is what I'm leaning towards as the culprit for this behavior. I've not got much money, but I can pick up an ECU if I have to.

 

[llamaking122]

check your connections at the battery and try new terminals. sounds to me like a loose wire for the ECM

 

[Tony H]

Alright, I've got a '94 ranger with the 4.0 OHV, 5 speed, it's relatively solid, but we're hunting a misfire, and have replaced the FPR with no changes, it'll do it with the MAF plugged in, but won't without, and I picked up a new MAF, it didn't change anything, so I returned it. New Fuel Filter as well.

Anyway, on to the issue at hand. I was on some back roads one morning, avoiding freeway traffic, when I come across a deserted stop sign, so when I leave the stop sign, I give it some right foot, just for kicks, really, and I hit 3500-400RPM in 2nd gear, and the ignition just shuts right off, radio keeps going, gauges all flatline, like I'd shut it off, I let off the gas and it instantly comes back, MIL not on, no idiot lights, nothing. Happened again last night, coming off a stoplight, I'm not even goosing it, and 2000RPM in 2nd gear it does it again (at this point a mechanic has looked at it but can't figure it out without replacing parts, his guess if ford programming, but we know it reacts to throttle input) so I immediately let off the throttle, and it's back up like nothing happened, I end up catching the next light, and I come off the light like the bed is full of fine china, and at 1900 RPM in 2nd gear, it tries to do it again, but I caught it before it did anything more than blip.

This is a frustrating and possibly dangerous issue, and I've got to drive 300+ miles per week. This truck has obviously been victim to some hoonery, judging from the muddy water and sand in the radiator, muddy water in the PS lines (all better now). So we can assume the ECU has been submerged, and that is what I'm leaning towards as the culprit for this behavior. I've not got much money, but I can pick up an ECU if I have to.

In neutral, just reving the engine.. will it cut out at the magical 2000 RPM?

 

[Slysdexia]

In neutral, just reving the engine.. will it cut out at the magical 2000 RPM?

No, it won't. I replaced the battery terminals (the nuts were being pulled out, leading to loose connections) and reseated both the TPS and ECU connectors. It changed the behavior drastically, but proceeded to do it just once while cruising at 65MPH, didn't come back till I pushed the clutch in, then didn't do it for the remaining hour of driving. I've subsequently cleaned the TPS pins and connector, as there was considerable corrosion there. I haven't driven it much as yet, but the issue isn't back yet.

It's still got this maddening low RPM stutter, if you goose it below 1500RPM it just falls on it's face, but won't do it if you disconnect the MAF. Which I just cannot figure out, nobody seems to have had this issue.

 

[TedJ]

Check the EEC relay in the box under the hood just for the heck of it, it provides power to the computer and fuel pump relay, and they do get old after awhile. Mine started failing to engage every 8th try or so at one point. Don't replace it with one of the cheap POS imported ones, horrible failure rate on those.

Otherwise you're just going to have to chase wires and look for things that look wrong, wiggle wires, etc. You can insert a test light at certain points in the ignition circuit and tape it to the window or whatever, so you can see if that specific portion of the circuit loses power when the problem is occurring.

Pretty soon you will be able to keep halving the amount of wiring you need to cover and you can close in on the problem... provided the problem wants to occur....

If the radio keeps going, then the battery cables would seem ok or it would cut out too, but if the ends were corroded the entire cable may very well be corroded internally too. They like to do that. NAPA replacement cables are the best, there is a thread on them...

You can also check if some imbecile installed some type of remote start/alarm and really messed up the wiring under the dash.

One more thought, get a large prybar/angry gorilla/ strongman and try to rock the engine back and forth. (or at least wiggle the wiring around) It seems like the drivetrain movement while accelerating might be doing something.... maybe you can reproduce it manually at idle....

And the shudder, look for air leaks like a crack in the intake pipe or vacuum leak, PCV tube, etc.

 

[Slysdexia]

Check the EEC relay in the box under the hood just for the heck of it, it provides power to the computer and fuel pump relay, and they do get old after awhile. Mine started failing to engage every 8th try or so at one point. Don't replace it with one of the cheap POS imported ones, horrible failure rate on those.

Otherwise you're just going to have to chase wires and look for things that look wrong, wiggle wires, etc. You can insert a test light at certain points in the ignition circuit and tape it to the window or whatever, so you can see if that specific portion of the circuit loses power when the problem is occurring.

Pretty soon you will be able to keep halving the amount of wiring you need to cover and you can close in on the problem... provided the problem wants to occur....

If the radio keeps going, then the battery cables would seem ok or it would cut out too, but if the ends were corroded the entire cable may very well be corroded internally too. They like to do that. NAPA replacement cables are the best, there is a thread on them...

You can also check if some imbecile installed some type of remote start/alarm and really messed up the wiring under the dash.

One more thought, get a large prybar/angry gorilla/ strongman and try to rock the engine back and forth. (or at least wiggle the wiring around) It seems like the drivetrain movement while accelerating might be doing something.... maybe you can reproduce it manually at idle....

And the shudder, look for air leaks like a crack in the intake pipe or vacuum leak, PCV tube, etc.

Well, while it did cut out completely this morning (was checking to see if it would do it in neutral, it did, and did NOT want to crank back up), once I got to work, it didn't misfire the way it had since I got it (the shutting off is new).

I'll definitely check the EEC relay, as none of them match under the hood (was a fleet truck originally, 75k in 3 years, then owned by someone who abused it), there's a little screwy wiring under the dash, but that's for a radio or something that sat between the seats that's no longer there. All other wiring under the dash seems to be intact and unmolested.

I've replaced the PCV valve and the vacuum connection to it didn't look too bad, but there's no real downside to checking for tiny cracks in those hoses. The intake pipe is fine, but the air box is just mangled, it's tabs broken off.

You may be on to something with the engine movement, and I happen to be my own angry gorilla/strongman, so I'll check that for sure. Tt might help explain the inconsistency, who knows.

 

[zimmyjim]

fuel pump? mine would run good, then it would go to spittin and sputterin all of a sudden, then it would run fine for a while..on and on......new pump fixed it. ebay $30..z

 

[Slysdexia]

Well, on the way home (thankfully, only 8 miles from home on a 140 mile trip) it just died and stayed that way. Cranking and cranking, it fired once or twice, started once but as soon as I let the clutch out it died, and that was all she wrote. The next morning, it starts up fine and runs strong, I park it and let it warm up thoroughly to see if it's a bad crank position sensor, and once warm it DOES start having trouble again, but really inconsistently. We go get a replacement sensor, and from then on it won't run, inconsistent spark, only giving single injector pulses per key cycle, and sits with 12.2v positive on BOTH pins of the injector plugs key on engine off. Swapping between the new and old crank position sensors doesn't change the behavior at all.

It would run horrifically on ether, blowing black smoke and pinging, but only for a second or two. Suddenly we got it to crank, it sat and idled beautifully, then as we waited for it to warm up again, it just kicked off like I'd turned the key. We pulled the ECU out, and it smells funky, the power regulators are all rusty, all showing signs of significant heat. The PCB is starting to delaminate and is discolored in many spots, including around one bank of legs on what I'd guess is the primary processor, and under several capacitors.

Every time it got power, the fuel pump kicked on, made good pressure, even during starting, so we ruled it out. Sucks that it's the ECU, but what can you do?

EDIT:
Forgot to mention, swapping the relays around, whichever one was put into the ECC slot got REALLY warm, I think that indicated the ECU drawing some significant current despite not even running, not sure if that's significant, but I think it's indicative of some internal failure on a silicon die somewhere inside.

Throughout all of this, the check engine light has never come on, except when it was cut out. Though once it had finally stopped running at all, it would slowly flash when cranking. I did have it into a shop for a while and they had it for a couple days and couldn't replicate it at all, and there were no codes to be read.

 

[zimmyjim]

yep...pretty much the same problems with my truck...
changed nearly every sensor with no luck.
then out of desperation i bought a fuel pump
and its ran great since.
it would be well worth the $30 to try a new pump if
it hasnt been changed already,
and it only took an hour or so to change..
fuel pumps will cut out like that..even more so if
ur running low on gas ....and theres no code
that i know of for a bad pump....zimmy

 

[Slysdexia]

yep...pretty much the same problems with my truck...
changed nearly every sensor with no luck.
then out of desperation i bought a fuel pump
and its ran great since.
it would be well worth the $30 to try a new pump if
it hasnt been changed already,
and it only took an hour or so to change..
fuel pumps will cut out like that..even more so if
ur running low on gas ....and theres no code
that i know of for a bad pump....zimmy

The pump primed every time, and maintained good pressure throughout (we even opened the pressure test port while cranking, it tried to soak the engine instantly, we took a break). There was fuel vapor coming out of the exhaust pipe after longer periods of cranking (after which we let it sit for a while). The capacitors on the ECU don't look good, and they're electrolytic, which means they've not got the best lifespan, get much past 6 or 7 years, and they can begin to degrade, or remain fine only to let go completely in a short period of time.

 

[TedJ]

So then did you meet with success by replacing the ECU? Just going through some old "Reply to thread" emails....




Just to satisfy the 'ol curiosity....

 

[Slysdexia]

Well, the ECU didn't help. what it ended up being was the wiring for the crankshaft position sensor having melted the insulation and allowed the wires to short. Replaced he wiring from about 2" past where it comes out of the harness down to a new connector, and it's good as gold.

 

[TedJ]

Ah, success. Interesting that even though the ECU was toasty it was still working just fine. Good to hear you got it back on the road.