I've been doing a lot of research across different forums. Some seem a lot closer to my issue, none are exact. I'm sure it's something electrical, but there are still so many places to look, it'd help to narrow things down.

1993 7.5L F350 with E40D


SYMPTOMS

It started shifting hard and late. When I say hard, I don't mean whiplash, launch you into the dashboard hard-- just obviously not functioning normal, makes the truck lurch a little.

All shifts if I keep my foot on the pedal like I normally would are at least ~300-500 RPM late. If I lift off the accelerator at the right moment, the shift is usually pretty smooth and not very late, feels more like I'm just operating a manual transmission (you know, the little hiccup between shifts when you put in the clutch and let off the gas).

Shift between 1-2 is the hardest and latest, needing to be around 2400-2500 RPM before it'll shift with a lurch, but if I let off the accelerator, I can get it to shift usually more smoothly at more like 2000 RPM.

2-3 is definitely harder shift than usual but not as bad as 1-2, and if I let off the accelerator at the right time, it's usually pretty smooth.

3-4 isn't very bad most of the time-- it's pretty normal, really, I don't even have to let off the accelerator to have a smooth shift usually, but maybe I'm not accelerating very hard at that point anyway.

I do notice a little bump when it downshifts into first-- definitely wasn't there before, but small enough you could miss it if you're going over a slightly rough road. No other downshifts cause this.

One thing I have noticed is that the first 1-2 shift of a trip is always really bad, requiring 3000+ RPM before it'l lurch hard into second. But this is only the first shift after ignition, even if the engine is still warm from having recently been run. If I get back down into first and accelerate to get into second again even just a couple minutes after the first shift, it's significantly less dramatic (2400 - 2500 RPM), and it'll shift mostly smooth if I let off the accelerator at about 1800-2000RPM instead of pushing it. Aside from this, the problem is consistent, no intermittency in the way it manifests, and it never goes away temporarily.

I can drive on the highway at 60 - 70 MPH in fourth/overdrive, no problem. Haven't taken it on the freeway since, but I've no doubt I could go 80.

No blinking OD light, no "limp mode" or at least what most people seem to describe limp mode as. I was pretty alarmed at first, but after having read a lot of posts describing worse problems, seems my hard shifts aren't as hard as a lot of others.


OTHER CLUES

Speedometer and odometer work perfectly-- no bouncing or erratic readings.

I do get a code 452 with my reader, which is the code for the VSS, though I've read enough about that code now to know it's just the signal the PCM is getting is bad and doesn't necessarily mean the VSS is bad. I had the VSS/RABS sensor in the rear diff pulled and inspected, and it didn't have any metal fragments or obvious damage, and the fact that the speedo works perfectly indicates the VSS sensor must be working (right?), so the fault must be between the PSOM and PCM or the PSOM itself... I think.

I don't remember if I ever tried using cruise control in this truck before this problem started, but I tried testing cruise control to see if it can hold speed or if it would wander, and cruise doesn't work at all. I can't even get the light to go on. I looked up how to do a cruise control test (key on engine off while pressing the speed control off button), but nothing happens. This could be incidental, but I understand the systems are related, so I mention it.

Oh, and my buddy did maintenance on the tranny back in August, replaced seals, filter, &c. He said the magnet was clean, no shavings, no other issues. It's shifted well until now.


WHAT LED UP TO THIS

Now, let me describe what happened that led up to this problem because this didn't just develop out of the blue:

I got this truck in July of 23. Its fuse block and parts of the harness were in pretty bad shape, so I found a donor wiring harness from a 92 F250 and had a buddy who's a 30-year mechanic swap the harness. He drove it back to my place that night (he's just a street over, so less than half a mile but would have definitely gone into second gear and noticed this issue if it was present), and he didn't notice anything weird about the shifting then. It was pretty late, and he was a little rushed trying to get multiple projects wrapped up that day, but having to get to 3000+ RPMs to get into second is hard to miss.

When I opened the truck door that night, after a minute or so with the driver door open, I noticed smoke coming out of a custom overhead lighting unit wired to the courtesy light circuit and pulled fuse #8 to cut power to the dome lighting. Turns out the prior owners who had that custom lighting unit installed used thin speaker wire to hook up some of the custom lighting, didn't properly secure this wiring above the doors, and it fell in the way of one of the screws when my buddy was reinstalling a panel after finishing up the harness swap, which grounded the circuit to the body and caused at least 15 amps to surge through the wire anytime the doors were open. My buddy didn't notice it because he didn't leave the door open very long like I did. The prior owners also put a 25 amp fuse in #8 probably because they added several power-hungry map lights for the rear seats and may have blown the standard 15 amp fuse with all of them on. The 25 amp fuse didn't blow, of course, and all that crappy speaker wire melted. When I swapped the #8 fuse to a 15 amper before I ripped out that wiring, that fuse blew immediately. Anyway, I finally had time enough to rewire the entire custom overhead lighting console after a few weeks, replace the six power-hungry custom map lights with LEDs, and reinstall the unit. The truck sat on my fairly steep driveway for about three or four weeks during this time not being used at all. I think I started it once at some point without fuse #8 installed but didn't go out of park, just let it idle for a few minutes. She fired up great the first time after finishing the rewired lighting unit, but first thing I noticed going out of the neighborhood was the shifting problem I described above.

CONCLUSION AND QUESTIONS

So I think the obvious things to check for are related to the new harness-- broken or pinched wires, maybe PSOM or connectors not perfectly reseated or damaged during reinstall - though my buddy likely would have noticed the poor shifting on his drive back to my place if there was a problem with any of that after he finished the job.

I'm not ruling out potential problems with the new harness, but I've wondered if somehow the whole courtesy light overcurrent fiasco could have done something here since that happened immediately after the truck was returned to me and before I had the chance to take it anywhere. I wonder this because the courtesy AKA dome lighting circuit shares the same fuse as the PSOM. It seems unlikely they could affect each other in spite of sharing the same fuse, but I don't pretend to know that-- is it possible? Or this also seems unlikely, but could me running the truck in idle without fuse 8 for a few minutes have done something to the PSOM, or even the PCM? I'm perfectly willing to send the PSOM in to be rebuilt or replace it, but it sure would be nice to be more confident that's the problem before taking out the instrument panel and dropping the money.

My buddy'll be taking a closer look again, hook up his fancy computer to watch input/output voltage/current values as I drive, but while I'm waiting for his schedule to open up, I've been trying to see if I can help speed up the diagnosis and save him some trouble, so any recommendations/insight are greatly appreciated.

 

Code 452 will cause late and harsh shifts. Either the VSS (vehicle speed sensor) is bad, the wiring to the sensor is bad, or the PSOM (Programmable speedo/odo module) on the back of the instrument cluster is bad.

All those other checks you're planning are fun, but they won't help fix this. Find which one of what I listed is bad and fix or replace it.

 

I have basically the same problem in my 1995 F-150 4.9 with E4OD, but with a few twists. At first the trans would "neutral out," i.e., shift into neutral during a shift or just driving, but shifts were hard too. Speedometer worked fine, overdrive worked fine and the OD light didn't flash. Checked codes, had a 452 and another one for the neutral safety switch/location sensor thing on the transmission, so I put in a new VSS and had a reputable transmission shop replace the neutral safety switch. It looked pretty easy to do, but the guy only charged me $50, so I let him get greasy. He replaced the connection to the VSS and checked the wires too. Didn't find any problems there. Anyway, all codes were cleared. After that, no more "neutral out" but the shifts, both up and down, got harder, or at least more noticeable and the code 452 came back. Swapped in another VSS, cleared the codes, didn't make any difference. Got a "known good" (well, so they said) PSOM from a salvage yard, no difference. Functioning speedometer, without the needle bouncing, seems to indicate neither my old PSOM or the used one from the salvage yard is bad. Now the salvage yard guy did say that these years of Ford's E4OD only work well with the factory VSS. And who am I to doubt him? He was wearing a greasy blue work shirt and chewing tobacco, so he must have been a qualified expert, right? In any case, that part, by Motorcraft, is discontinued and none seem to be available as New Old Stock. Took out the VSS altogether and the speedometer quit working, but otherwise, still shifted hard. Put the VSS back in, cleared the code again and speedometer etc., worked fine, but still shifted hard. At this point I feel that I've almost shot all the ammo from the parts canon. Only thing left is the PCM and I'm not getting any trouble codes indicating that it could be bad. Could it be that I'm doing something wrong? When I install a VSS I grease up the differential hole and the rubber seal on the VSS but the VSS still has to be tapped firmly with a rubber mallet to get it to go in. Could that be breaking something in the VSS?
Keith

 

I ended up sending in the PSOM to Module Mechanics to be rebuilt. I didn't see any corrosion or bulging capacitors, but I sent it in anyway. It was destined for Colorado, but the USPS in all their efficiency sent it for a scenic trip through Georgia, so it's taken an extra week to arrive.

In the meantime, I managed to find pinouts and wiring diagrams and used a wire toner to trace the wire from the PSOM through the firewall into the engine compartment. It goes to both the PCM and the Speed Control Module as the diagrams say it should, so there isn't a wiring fault. At this point because the speedometer worked perfectly it seems it couldn't be an issue with the VSS, and since the wiring between the PSOM and the PCM is good, it has to be the PSOM itself. We'll find out sometime next week when the rebuilt PSOM is sent back and I put it back in (unless USPS decides to route it through Hawaii or Alaska on the way back). I really hope that's it because I've exhausted the other possibilities. I guess it's possible there could be a break somewhere in the wire insulation between the PSOM and the PCM allowing another bare wire to touch it and mess with the signal. I was not able to find any other wires carrying the signal elsewhere, but something like that would require additional tracing. I can try chasing that unlikely scenario if the rebuilt PSOM doesn't solve this problem, but let's hope it was just the PSOM like it seems to be for so many other problems like this.

Oh, I did test unplugging the RABS module behind the glovebox as I read that sometimes the RABS input can mess up the PSOM output signal if the RABS module is faulty-- no change in behavior.

Will update once the rebuilt PSOM is back in.

For others who may have similar problems later on and want to use the diagrams I found, they're linked below (some are for Broncos, but they should have the same wiring and pinouts as the F-series of the same years, and I understand at least 1992 - 1995 wiring should be pretty much the same-- not sure how much the OBDII introduction in 1996 might alter wiring not directly tied to the OBDII port like the VSS to PSOM wires and the PSOM to PCM wires that I've been tracing):

• PSOM connector pinout
• PCM pinout, firewall connector pinout, PCM wiring diagram
• More detailed firewall connector pinout
• VSS system wiring diagram
• Alternative VSS system wiring diagram

 

Well, glory to God, it's working. Not at all how I expected, though.

Got the PSOM back a couple days ago, put it back in and took her for a spin-- no dice. At best maybe the shifting was less harsh, but that could be my imagination. Still got code 452, still shifting late and rough.

I spent a lot of time tracing out the circuits, testing resistances, pulling off firewall connectors and testing every pin for continuity between itself and the PSOM output wire (I was hunting for any wire that could somehow be connecting to the PSOM output wire through worn insulation or otherwise, and as far as I can tell, the wiring harness is in great shape-- I can't find any evidence of any other wire contaminating the PSOM output).

In my tracing and testing, I disconnected the speed control module (AKA cruise control), double-checking that the PSOM output wire (gray/black 679) still had continuity with it and the PCM. But for the heck of it I left the speed control module unplugged and tossed the instrument cluster back in and took her for another spin. Well, tug my beard, it's shifting smooth as butter! Uncertain whether this was a fluke caused by me bumping harnesses around and retightening firewall connectors, I tested plugging the speed control module back in, and it immediately started shifting problematically again. Unplugged it, and it's smooth sailing again. So the speed control module was the culprit this whole time.

I haven't seen the speed control module as a potential source of trouble for the PSOM-to-PCM connection on any other thread or article-- and I've read more than my share. High chance that it still has something to do with the new wiring harness causing the speed control module to pollute the PSOM signal to the PCM since the only thing that's changed since before it worked fine was the dash wiring harness. Or maybe it's a fluke and the speed control module started acting up on its own about the same time as the harness swap, or it somehow got fried during the dome lighting overcurrent fiasco (seems unlikely). Obviously the PSOM output wire (gray/black 679) connects to both the PCM and the speed control module, so that seems to be the likely method of it messing up the PSOM signal, but I have absolutely no idea how.

I'm not in a rush to get speed control working again (I hadn't used it before this so don't know if it worked before), so I'll be leaving it disconnected for now, but I figure I'll probably start by researching how to test the module by itself with inputs/outputs, see if it's faulty. Or just replace it if it's cheap enough and see what happens. If the module ends up still being good, then perhaps there's a wiring problem from the other wires that connect to the module causing the module to misbehave and mess up the PSOM signal, which will be a whole different task to trace at another time.

I was at the point that I was going to try bypassing the 679 wire and run my own through the firewall to the PCM, either cutting the wire and splicing at both ends or pulling the pin out of each connector and replacing it with the new wire. I'm glad I didn't because that would be ugly, a lot of hassle, and I was going to splice it to the speed control module as well, so I'd have just run into the same problem and gone bald ripping my hair out.

I'm not too broken up about having my PSOM rebuilt. Price was reasonable, and at least now I know it's 100% back up to spec. There's a good chance it would have failed in the next few years anyway based on so many other threads where a rebuild fixed the shift issue. I did ask them to test it before doing any fixes, and while they didn't say the signal was obviously toast, they did say it was definitely exhibiting common degradation of the square wave signal.

Oh, one thing of note that may help others in the future is that I measured the resistance of the VSS/RABS sensor on the rear diff in my desperation even though I was pretty certain it wasn't the sensor much earlier in this game, and it came out as 1227 ohms. I've read a few places that it needs to be about 1330 ohms, but apparently being off by ~100 ohms isn't enough to be a problem.

Anyhow, if you're pulling your hair out trying to solve a similar problem, it's easy and cheap as free to disconnect the speed control module to see if that clears up your shifting issue-- easy to reach since it's right there at the top driver side of the engine bay next to the EECIV test connector.

 

My hard-shifting issue was fixed by replacing the powertrain control module. Shifts smooth as silk now.
kjhansen

 

A year later your truck still good? what truck did you fix this on, and what was your issue, because I've been having crazy tranny shifting issues that i've been wracking my brain to solve. I have a 1994 f250 7.5 e4od

 

You need to read the codes to be able to fix this. Here's how: www.troublecodes.net/ford

 

My 97 F250HD 4X4 with a 5.8 E4OD shifted hard into second and a little bit in third. Also hard going into reverse. It is not as hard as if your speedometer was out but enough to take notice.I
read and tried everything minus a transmission replacement and learned to live with it. If I disconnected my battery and reconnected it, the problem would go away but return after a few short drives.
i lived with this for over seven years!
One day I decided to replace all the components in the cooling system because the antifreeze was brown and the truck started running a little warmer. While doing this, I noticed a vacuum line running from a solenoid by the throttle body to the charcoal canister was in bad shape but didn’t change it. Weeks later, I stumbled across a vacuum line in my garage that looked like it would fit it and used it on the truck. After a few drives I noticed the shift problem was gone! If your having a shift problem like I described, take some time and look closely at your vacuum lines on the engine and don’t discount any of them. I felt like a shlep putting up with this only to have a vacuum line causing it.
I’m new to this site but if you have any questions about this issue just ask.