Hi everyone, I have a 1991 F150 E40D with the 5.8L. I am having issues with my trans where 1, 2, and R seem to work fine. D felt like it was locked in 4th. When it was cold it ran okay, but whenever it heats up D is only driveable above 20 MPH and 1/2 gears both start to feel like they have TC shudder. After lots of research I replaced my shift solenoid and checked the valve body to make sure none were stuck, they all moved freely. I also replaced my TPS sensor because of code 121.

Now whenever I drive my truck behaves the same on takeoff (a bit of a shudder) and it seems to be manageable at 40mph. It doesnt kick down into gear if I floor it and sometimes it shifts funny.

Fixes I have done (Because it is old and I'm also chasing the trans issue)
Plugs, wires, coil, distributor, vacuum lines, shift solenoid, shift solenoid harness, TPS sensor, fuel injectors, Neutral safety switch.
I pulled codes: 6 CYL, 311, 538, 536, 632 doing KOER and i cleared my KOEO because it was just the 121.
I have NOT fully replaced trans fluid, only did one drop and fill for about 6 qts worth of fluid. This trans fluid is probably original and completely gone bad. I think it could be worth draining the converter and doing all the fluid. I also have NOT replaced/checked my axle speed sensor, I know they can contribute and my speedometer is not "rock solid" it can occasionally wiggle.

I would LOVE to get a couple years out of this truck before I inevitably have to rebuild my trans... please help!

On a side note I feel like my fender mount starter solenoids keep going bad... is this a ignition switch problem or a fusible link issue? The truck always starts when I jump the solenoid but after a few days the solenoid wont start by the key anymore.

 

When it doesn’t work with the key, have you checked to see if the s wire on the solenoid is getting power?

 

What voltages do you have at closed and WOT? Was the MLPS lined up correctly so that you are getting the correct voltages for each gear?

6 CYL? Is it the correct computer for the truck? You cleared the codes after the TPS was replaced and the code didn’t come back so you moved on to the KOER test?

Is the battery good? Maybe it’s weak and that’s why it doesn’t start and/or the ignition switch is bad. The

 

A 1991 model year truck has a mechanical speedometer/odometer. No physical or electrical connection to the rear axle vehicle speed sensor that is used for only the rear anti-lock brake system (RABS).

The cylinder display on the KOER tests is frequently wrong. Aftermarket code readers are hit or miss displaying the correct value.