92 F-250HD RWD 460 E4OD ExCab XLT 155"WB 4.10 Limited Slip

Description of problem: During 2-3 shift, under mid-throttle, E4OD slams into gear very hard. Light throttle is just a clunk. I'm afraid to try WOT. 3-4 can be very firm (truck lurches forward), but no hard slamming. Under mid-throttle, it also seems to hold 2nd and 3rd longer than it should. If I notice RPM going a bit high, and lift gas for a second, shift will be firm but not dramatic. When vehicle is cold, shifts are predictable and smooth.

While towing recently, I made the mistake of pushing the O/D Off button without letting off the throttle. The truck bucked and shuddered violently during the 4-3 shift. I'm still amazed the transmission didn't explode right then and there.

Scanner:
KOEO: 11
KOER: 11
CM: 11
Bosch OBD1015 Code Scanner; it has produced reliable readings in the past, and helped diagnose a malfunctioning cat and alternator (Codes 95 and 65 respectively).

Relevant previous repairs:
4,000 miles ago:
- Timing checked/adjusted
- RABS sensor replaced
5,000 miles ago:
- VSS replaced
18,000 miles ago:
- Rebuilt Transmission w/HD converter

Theory: One or more resistors/capacitors/diodes on the PSOM is faulty but not blown so the ECU doesn't know about it. It's somehow causing the ECU to send shift signals without the attendant "unlock" signal to the converter.

PSOM version is E 03. It has no digits after, indicating that the previous owner used up all the resets, or it's such an old version it has no resets. The Conversion Constant is 9.84, and according to this chart it's the factory setting for my stock 235's. I've noticed the speedometer reads about 5mph too fast.

I'm hoping someone can poke holes in my theory about what's wrong. I'd like to make sure I'm not missing something before dealing with the Pain-in-the-SOM.

Also, can anyone tell me whether EEC-IV is supposed to retard ignition or cut injector pulse width during shifts? If so, should I be checking this?

 

If you are getting 11's, those are pass codes. All is well.

There are no "mysterious" electronic component failure modes invisible to some devices, but not others.

I think your hard shifts may be the result of high line pressure in the transmission, not converter lockup. If you want to diagnose the transmission, hook up a pressure gauge to the test port. It also helps to know that your transmission is running at an appropriate temperature. A temp gauge is a welcome addition and you cannot have too much transmission cooler.

You may find it interesting to monitor the EPS signal from the ECU to the transmission. Measure it as current, not voltage! Takes a bit of fiddling to rig a test set up. If I recall correctly, no current = highest line pressure. The plug at the transmission is notorious for insulation failure. A short here can cause all sorts of shifting problems and repair kits are available.

 

Do you have speed control(cruse) on your truck. If you do, activate it and see how it will hold speed. If the PSOM is not sending out a good speed signal the speed control most likely will hunt the set speed or not even set at all.

Usually just before a code is set the above tranny shifting problems will happen. Once it gets bad, the OD indicator will flash and tranny goes into limp mode due to bad speed signal.

To test this, find another PSOM and install it to see what happens. Just rember these PSOMs are getting up in age and you can get another "bad" one from the junkyard.

 

 

I'll do the pressure check first, of course, but I expect to find it normal. The transmission only has 18,000 miles on it and it was a complete rebuild; right down to a new wiring harness. The valve bodies & solenoids were upgraded to the best units available in 2014. I had all this done specifically to address the hard shifting problem, otherwise I'd have just chosen a normal rebuild with upgraded converter. So it seems a little redundant to go through the transmission *again* (other than the line pressure check, just to be sure). I agree about cooling and temp gauge. It's on the to-do list, but the hard shifting seems more urgent at the moment.

I hadn't considered the ECU itself for troubleshooting. It seems to be doing fine running the engine, but maybe that doesn't matter. If line pressure is high, I'll take your advice and try to measure EPS (this is the signal sent to solenoids, yes?) current (amps, I assume).

 

Yes, it does fine in cruise. Holds speed correctly and it's very stable.

I've had the shifting problems for almost 40,000 miles now, through two transmissions. I keep checking codes (and finding other things to fix, so it's not been for naught). OD indicator has never flashed. It's never gone into limp mode. Seems like it would have progressed to this point already if it was the PSOM, so thank you; I think we're ruling it out as top possibility. I'm looking more to faulty solenoid signals from the ECU.

If it does come down to PSOM, I'll just rebuild it. I agree with your assessment that age makes junkyard electronic parts super questionable. Plus, I'm comfortable soldering small parts and am capable of finding the correct components online. The added benefit is my odo remains original and true.

I don't mind putting effort into this vehicle. It's a 250HD. Getting the same capability in a newer truck with any kind of warranty left is north of $30k. I could spend that on this '92 and have a beautiful, comfortable vintage rig that turns heads.

 

Ok, as the speed control works with out any issues, that rules out the PSOM(from my experiences). The PSOM sends speed data of 8000 pulse per mile. That goes directly to the ECU and speed control servo. May want to pull the ECU out and check for bad/leaking capacitors. Another thing could be is the alternator has a weak diode and is giving out some voltage ripple. That has caused the E4OD to shift in weird ways from other posts here.

 

ECU seems to be the next logical step. Alternator is new.

I'll report back after I get a chance to do a line pressure check and visually inspect the ECU.

 

You might try unplugging the Speed Control Amplifier, plug C216.
Also leave the Rear Anti-lock Brake (RABS) Module unplugged C277 while working on the problem.

If still having issues with them unpluged unplug the passenger side plug on the transmission, remove the plug shell and check out the wires as they go into the plug C1048.




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Rebuilt or not, I have seen a 500 mile trans have pressure problems. A piece of clutch fiber got passed the filter and was just enough to stick the pressure regulator valve.
And while it ultimately came down to a manufacturer defect in the clutches, they were not slipping so if the pressure had not been ungodly high no problem would have been noticed at that point.

 

Based on the hard shifting issue with my 1993, the PCM has detected slippage of the TCC and has increased line pressure in an attempt to prevent damage to the transmission. To test this, disconnect the battery for a while to clear the error codes from the PCM. when you drive it note if the shifts are normal and not harsh. This may only be a short time before TCC slippage is detected. The best way to check this is to monitor the line pressure at idle when it is shifting bad and then after resetting the error codes.

Keep an eye out for my update to my post about my harsh shifting.

 

Also, if disconnecting this plug, get a mirror and position it so you can look down inside of this connector to see if any atf is leaking through and/or collecting there.