OD Shenanigans
 

I am stumped on what is causing my OD issues. My truck will intermittently not shift into OD or will shift out of OD at highway speeds. I bypassed the TPS with a POT and that worked for a few days then the problem came back. I hooked up a switch to the OD solenoid and grounded it at highway speeds and still no OD. Please help point me in the right direction.

The OD solenoid is powered by the A21 splice (same power as the FSS) and grounded by the PCM.
The solenoid in the transmission has to be good.
Connections have to be good.
Inputs to the PCM to calculate OD shifting have to be good:
TPS
CPS
VSS
Engine temp
Transmission temp
Power and ground to the PCM have to be good.

<edit> didn't see you had tried to ground the solenoid. If you have power and ground to the solenoid and no OD, you have internal trouble in the transmission.

hope it helps
John

Thanks for the help! I was thinking it was in the tranny. I am just unsure if its the OD solenoid, or something else. Looks like I have a trip to the tranny shop in the future.

I just had this problem. Turned out for me it was the crankshaft position sensor going bad. Would cut in and out when it heated up to operating temp. The computer couldn't see that the engine was running so it wouldn't send a signal to shift the OD.

Tucker, if you had grounded the solenoid, it would have shifted to OD. Different problem.

Yeah, you're right j_martin. I just thought I'd share what happened to me to let it sink into the collective consciousness of the board.

Just wondering if doing a transmission flush and adjusting the bands would help or if it going to require a full rebuild. There is no shudder and it shifts nice and firm, it just wont go into OD or if it does it will slip back into 3rd on the highway.

It would be very unusual for those symptoms to be internal to the transmission. If you're not up to systematically testing the wiring involved, you need to get some help. Guessing is the most expensive and least effective path to a repair.

I went thru pretty much the same thing with my pile of junk, this was the fix for me...
https://www.dieseltruckresource.com/...oo-t74673.html

what computer?

For ATF fluid is it best to avoid ATF +4? I have read that ATF +4 can cause issues. What would be the right fluid to use?



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92 W250 LE Regular Cab

DEXRON III is the factory suggested fluid. I susect ATF +4 would make it shift smoother but i have never tried it.

My factory manual says ATF plus, with Dexron II an allowable substitute if ATF plus isn't available.

When my transmission was overhauled/upgraded, Kole put in Amzoil Synthetic Multi Vehicle Transmission Fluid. Says he wouldn't warranty it with anything else in it.

theres a pressure port on the left side of the trans put a gauge on it jack it up and run it untill its supposed to go into od. we had one that wouldn't go into od all other gears worked fine and we put a gauge on the od port we found we had 26psi when it tried to shift into od, found the seal was bad on the od piston, we just replace the seal and od clutches and we were good to go.

Well I took it to a Tranny shop this morning All the way there the OD bypass switch hooked up worked and it would go into OD but it was cold. The tranny shop put it on a scanner and told me to check the wiring. Brought it home dropped the pan and changed the filter and fluid. Everything was tight , no lose OD solenoid. I checked the blue wire going to the OD solenoid again and it was going from 13 volts to 0 volts to 5 volts. I am guessing that the blue wire should have 13 volts constantly when the truck is running. And that is why my bypass switch is intermittently working If thats true where does that blue wire go? I am unable to find it when it goes up above the tranny. Thanks for all the help!![duhhh][duhhh][duhhh][duhhh][duhhh]

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92 W250 LE Regular Cab