I've got a 95 F250 E4OD with a lot of modifications. I have been dealing with this problem for 10-15 years but most of the time, life has got me fixing other more important issues. I've got some time now to resolve the one I am having.

Basically, I have a transmission that upshifts/downshifts great. I've got the ability to 'tune' the shift timing and quality of shift [soft/firm]. It seems that when I am towing at freeway speeds [50-60mph] there will come a time where the up/down shifts are violent. Extremely harsh. Not just one particular shift, but all of them. If I pull over and check for codes, I do not get any that point to my issue. If I do a hard reboot [ie, disconnect the battery, turn on headlamps] the transmission will shift fine until I get back up to freeway speeds for a few miles [5-10]. Then, it starts to shift harsh.

The shift timing is not effected. Seems to shift t the right place, it's just harsh. I hear about limp home, but it seems that I am confused what the computer will do in limp home. I read where the shifts will hang up. I also read where the shifts are harsh. Then there are places I have read where both happen.

I like testing and seeing results of the tests so I can feel confident what's going on. That said, I have swapped out every part of the transmission from stock. The stock transmission is sitting in the corner of my shop. I rebuilt the rear differential and installed a 4.10 gear set [was 3.55]. When I go through things, everything gets swapped out. That included the speed sensor.

Since I have owned this truck since 97 and I am committed to keeping this. One more year and I get Classic plates.

It's taken years to figure out when this harsh shifting occurs and what exactly is causing this. I suspect the computer is sending it to some type of limp home mode, but only with full line pressure. I have another EEC-IV computer for a spare and with that computer, it does the same thing. Since this problem has happened to two different transmissions, I do not believe I have a transmission problem. I have changed out the wiring connectors at the solenoid and shifter switch.

I do not have an issue with my odometer or speedo. Both work fine and are not erratic. I have disconnected the RABS computer but not the cruise control computer. I do have a break out box that I plan on hooking up, but since this problem happens mostly on a camping trip, I don't want that 'look' from the wife with all the test gear on the seat.

So, the question I have is.....Is there a limp home feature that just changes the shift quality but not the shift timing. If there is and there are no codes, where would you start to look? I plan on installing the breakout box and testing things without towing the 5th wheel. I suspect I will see nothing that excites me. I guess I would start at checking the speed sensor input signal at the EEC-IV computer. If I see everything good there, I would check the signal to the pressure control solenoid. That for certain would lead me to something. I suspect when it does shift harsh, there would be no signal. If anything, it would prove my theory.

One last thing and I do not believe it has anything to do with it, It seemed to start after I had some shop rebuild my transmission. I hate when I got to sublet work, but I really had no choice 15 years ago. I had no problems before that. I hate to say it seems to be an 'ever since' problem, but it is. At this time, I don't think there is anything that they did that caused this issue.

I have researched this, but I have not found anyone with similar issues or the final results if they have.

I am leaning on the PSOM. I was thinking about taking mine out and getting it rebuilt, but I am also thinking that if there is a chip issue, it might be better to get a used one to get rebuilt.

I can buy a stand alone transmission computer, but I really think that is a chicken ship way of fixing something. I guess, that will be my last resort but I would love to know why.

 

What does this mean? Are there codes, and if so, what are these codes? Code numbers, not descriptions.

Yes, most codes will raise the line pressure but not change shift timing.

 

The only codes I would get are the ones where I have to perform tasks [step on the brake, full throttle, etc].

Thanks for the input with the harsh shifting. I am not a programmer, but I suspect that if the control unit has acknowledge there is something wrong, there would be a code. I can say, I have never seen a code [I have a code reader] but I always hope to see a VSS code.

At some point, I will find the cause and report back. Hopefully with some test results too.

 

I rechecked codes and found codes 179/181. Those codes related to bank 1 O2 sensor and probably related to the leaking header gasket. On my list of things to do. Code 121 which is probably related to the 'tuning' I have done. I will certain check the throttle voltage and probably replace it [because it's too cheap not to]. Both of those codes are in the continuous memory.

 

I finally got some type of resolution with my transmission. Not really a factory way of fixing it, but it has worked for me.

Ever since I had my transmission rebuilt/repaired [early 2000's], I get a harsh shift. Usually 3-4 or 4-3. I tow and it happens only when I tow. I finally got fed up and elected to build my own. I got a 95 core transmission and put in all the heavy duty parts I could. 6 planet gear sets and a 4 planet gear set. All steel. Every clutch basket has more clutches. Some as many as 3 additional. There is also a Tugger shift kit. Basically, it shifted the same as before, but firmer. The only thing that is the same is the EEC-IV module.

I started to think, with all these parts that are suppose to make the shifts firmer, I was wondering if the stock EPC pressures were too high for what I got. I have a Tweecer but nobody uses that to play with the E4OD. Nothing I did helped. I eventually installed a trans pressure/temperature gauge in the dash [removed the trans temp gauge I had] and I found that if the EPC pressure was around 100 psi, it shifted firm. Anything above 130 psi, was getting harsh. Anything over 160 psi was not good what so ever.

I eventually found by changing the engine torque values [Engine Torque for TQ_Net Calculation] lower, the EPC pressures started to get lower. I eventually changed the values to 50% less and some of the higher loads, they are adjusted lower by 75%. Right now, the pressures are not much higher than 110 psi and the transmission shifts much more normal.

There are times where the EPC pressure is high, but not during an upshift. I suspect there are times Ford wants to see a high EPC pressure, manual low, downshift braking, etc and I believe they were not changed.

Anyway, those that have modded a transmission well above what Ford ever intended, it's highly recommended to find a control unit that can change the EPC current. As far as I am concerned, it was well worth the time/effort to put a pressure/temp gauge in the car. That additional data gives you facts so you can figure out what's going on.