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Hello
I have a 1991 f150 351w E4od with some weird shifting issues. The transmission was replaced in 2022 with one build from monster. It has roughly 50k on it. It started to lose lockup in 4th. Ran diag. And gave a code 99 " EPC circuit fault". After diagnosis my epc solenoid had high ohms. Replaced that and put a new filter in and code went away. Didn't fix the issue instead it got worse. I would lose reverse when at temp. Replaced the MLPS "neutral Safety switch" and TPS for good measure. Ran a pressure test and got some weird numbers. On start up all pressures read good in every gear. Tap the gas and idle pressure goes to 30 psi and all gears read really low. Turn the key off and restart and the pressures are fine again. I'm thinking maybe a sticking valve. But will admit I'm in over my head and don't know enough about transmissions.
It could be a sticking main regulator valve. It could also be loose feedbolts. Both of these problems can cause erratic issues.
The main regulator valve is in the main valve body. I don't have a diagram to show you which valve.
While the valve body is off, look up into the worm trails and you'll see the feedbolts. They need to be torqued correctly. If any are loose, you've found your issue.
Ok got time to pull the valve bodys off. Cleaned and installed. Didn't see any issues. Had one valve felt a little sticky. Pulled it out and cleaned. Had a little clutch material in it but not much. Retested the pressures and no real change. No reverse. I can blip the throttle and it will go to 30 psi in park. I can rev it and slowly let off it will stay at 60 psi. Hate to say it but I think its going to need to be pulled and have someone go through it.
Last edited by tpone; Aug 17, 2025 at 06:10 PM.
Reason: added attachment
I get that you are scared. We all have been there, but since you did not check them, you will probably have to do all that work again or have someone else do it for you. Don't forget the gasket that may break. The aftermarket manufacturers make a thicker gasket to help with warped cases.
Yeah that's why I didnt want to do that. Be my luck id lose one or get one in the wrong spot.
Lay a tarp down under the trans so if you drop one, you can find it.
6-10 FT-LB on the single feed bolt (overdrive clutch cylinder)
10-12 FT-LB on the two feed bolts that are side by side (Center support)
10 FT-LB on all 3 if you forget haha Do NOT guess! If you over tighten, you can warp the case!
It's broke now, you can't do damage by taking it apart.
If you take it apart, you will know if the feed bolts are tight or loose.
If not, you will never know.
If you loose a ball, get another one.
Nothing to be scared of.
Blocked off is fine but there should still be movement when the solenoid applies vacuum.
