My friend has a 94 F250 7.5L E4OD 2WD truck 94,xxx miles. Truck is in fantastic shape, he is the 2nd owner. This problem started suddenly. The truck starts and runs fine. Put it in reverse and get on it a little bit and it goes stupid, bucks, backfires, and the O/D light blinks. If you shut it off and re-start it, everything is fine untill you do that again. You can drive it all day long in forward gears and everything is fine. You can start the truck, unhook the MLPS, and then put it in reverse and do anything you want and everything is fine. We attempted to pull codes with two different code readers and got nothing, and I mean nothing. Starts to do the test and then just stops and reads 000. We have not checked the computer for leaking caps yet because it runs too good as long as you stay out of reverse. Anybody got any ideas? All comments welcome!

 

Pull the computer and look it over.

Failing that as the problem check the circuits for reverse make sure nothing shorting to ground or crossing circuits wreaking havoc for the computer to the point it simply can't deal with.

The fact it fails to run the self test and while in park suggests the computer as the problem.

 

That's what I thought, but was thrown off by the fact it ran so well as long as you stayed away from reverse.
We checked all the wiring and connectors on and around the trans but found nothing wrong. Cleaned the MLPS with electrical cleaner but it didn't help. Can a bad MLPS do this? Computer will be coming out tomorrow for a thorough inspection.

 

Yea especially for example if full of or soaked inside from being submerged in water, water jumping circuits could cause any number of problems/screw with a computer.

I don't recall some where around the 94 95 model year the MLPS was updated to be more water tight? to prevent that very issue.

 

I think we might unplug the MLPS and try testing for codes. I know this will throw a butt-load of codes, but IF we get codes that means the computer is still working. I'll update tomorrow.

 

1995....

 

Update. Unplugged the MLPS and the codes started pouring in, so the computer is working. He pulled and examined it just to be sure and he said it looked perfect. Got a new MLPS (new updated version, thanks for the heads-up danr and rla) and installed it. NOW............if you start it in park and go to reverse the problem is back, running poorly in all gears forward and reverse, check engine light(that didn't happen before) and flashing OD light(that did happen before). If you start it in neutral, you can go in any gear, reverse or forward, back to park, and it runs and drives just fine no problems as long as you don't shut it off. He is going to clear all codes and make it misbehave and then re-check codes and see what it shows tomorrow.

Any ideas?

 

I'm leaning toward transmission solenoids or wiring, but wouldn't it do it consistently instead of the way this one is behaving?

 

Pulled the codes today and here's what he got:

114 ACT out of self test range 0.3 to 3.7 volts.

116 ECT out of self test range 0.3 to 3.7 volts.

624 Electronic Pressure Control solenoid or driver circuit failure

625 Electronic Pressure Control driver open in EEC

636 TOT sensor voltage out of self test range.

10 Cylinder #1 Failed Cylinder Balance Test.

So what should I check first?

 

10 is to indicate it is switching from KOEO codes to CM codes.
so disregard the 10.
Trav

 

Was the engine and trans up to full running temperature for the self test?

If not you can at least for now disregard 114, 116 and 636.

I'd start with 625, correcting that one should resolve 624 with it.

Not sure if 625 is just misleading in its wording or if its a true reflection of the problem . The problem being internal to the computer itself as in "Control driver open in EEC". "in' being the key word in that sentence.

First thing I do is check that circuit between the trans and computer pin 38 (pcm) to pin 11 (solenoid pack) for contintiy/clean connections both ends (WHT-YEL wire).

Then check pin 12 at solenoid pack and verify its getting battery juice from to it and also pin 37 at PCM connector (red wire).

The PCM relay is the source for the red wire, it runs so safe to assume it at least leaves the relay as it should. Wire ties in at various places mid harness to branch out as needed. Make sure it does make it to both trans pack and PCM at the listed pins just to be sure.

If those circuits tests good you know they make solid connection as they should? then the problem is most likely internal to the PCM and it will need repaired or replaced.

His is a PCM as it controls both engine and trans, the codes definitions are incorrect as written as far that aspect goes, incorrect listing it as "EEC". (just in case that part was confusing in my post, code defined as EEC but me referring to it as PCM).

EEC = computer PCM = computer just depends on what's controlled by it. EEC is engine only/earlier models.

 

Yea, that code is a real red herring. I wish they would have designated a code indicating it's real intention instead of saying it is checking something it has absolutely no way of checking.

One thing I forgot to mention. If you cycle the key 3 times (on-off-on-off-on) and then start it, if runs and works perfect no matter what gear you shift in to.

 

The truck was warmed up to full operating temp, that clued me in to a possible bad PCM, but was looking for a second opinion.

Thanks for the info danr, I will check those things out. But I agree with your assessment of a bad PCM.

 

Thanks for the reminder on 10, Trav!

 

Yea the more info you provide such as cycling the key on off on off and codes for temps sensors out of range even though would be or should be right on points to the computer as the problem.

Either that or its got one heck of a power supply issue, check power to the computer and its main grounds. If checks out and those couple circuits, wouldn't hurt to spot check one or two of the temps sensors while he's at it, if find all as it should be then the computer would be number one suspect for sure.

If the computer hasn't been pulled for a visual inspection of its main board yet? then might better start with that checking it for obvious damage/failure that can be seen with the unaided eye.

Doing so might prove save him on the task of chasing down hand full of circuits/sensors for nothing!