1991 f350 7.3 idi e40d
I already made a post about this with all the details so I'll keep this update simple. My transmission doesn't want to shift down from 3rd and will constantly stall out when coming to a stop. To bandaid the issue i have been manually shifting bewteen 1st 2nd and D. On top of that a couple weeks ago, tranny started throwing a code (overdrive light blinking, as well as very hard shifts). Not sure how to read it but I'm planning on figuring it out soon here. It goes away if i shut off the truck and restart it, but still doesnt downshift from 3rd.

I had the tranny rebuilt buy a "cheap" shop in March 2025, and have been having the stallout issue since a few weeks after that. I took it back into the shop in october and they held on to it for 3 weeks only to tell me the problem is the TPS and thus not covered under the rebuild warranty (but they messed around w it anyway and said they couldnt figure it out.) So i bought a new NGK TPS and just put it in and calibrated it today. Reading 1.22v idle and 4.15v open throttle. That cleaned up a lot of slop, as the readings were waaaay off from when the shop messed with it. It was around .8v to 3.6v before i touched it. But still doesn't downshift from 3rd and wants to stall out.

Anyways without going into too much detail i don't trust the cheapo shop they have been very difficult to work with and cant seem to do anything right (Even replacing the battery and terminal connectors that was stolen while my truck was in their lot was too much for them apparently. Wrong battery and the connectors they installed were all butchered up and very loose.) So I guess I'm gonna try to read the code and see whats up, if i cant figure it out i will take it to a better shop for diagnosis.

I will research but any tips on reading the code is much appreciated 👍
thanks

 

You can use a jumper to flash the codes. Check it out!

https://www.troublecodes.net/ford/#accessmil

When I started manually shifting the C6 in my Bullnose truck it was on its last leg. I had to get it rebuilt.

BTW, do you still have your original FIPL? I'm not sure how well rated those NGK parts are.

 

It may be downshifting, but the converter is not unlocking. That could be a problem with the valve in the pump. If you drive down the road in OD, and hit the OD cancel switch, does it downshift?

Get yourself a Ford OBD 1 scanner. They're cheap.

 

Yes it will downshift when i turn off overdrive. There was a code for a tps issue which I replaced and calibrated and didnt fixe the problem. I also learned about the 3rd brake light causing shifting issues if its not working right and just had to rewire it today to get it to work but still didnt fix the issue. Also sometimes it will just skip 2nd gear when moving the gear selection from 1 position to 2 position and go right into 3rd, while still in 2 position. Kinda weird

 

i dont have the original one, i took it back to tbe shop after having this issue and they replaced it and tried to calibrate it but couldnt calibrate it right so they gave up. Which is interesting because it took me a few minutes to calibrate and i dont know sht. So i replaced the one they had just put in there anyways with the one i already had bought.

 

You must read the codes to fix this. Without the codes, the only thing you can do is start throwing parts at it.

 

Just pick your favorite transmission shop and get it there now while you still can.
Save yourself the tow.