Vehicle 1992 B250 w/318 v8. From google images it appears to have an a518 transmission, though some of the details in the diagram I'm looking at are off.
Issue: Poor MPG + no overdrive

I recently noticed my overdrive seems not to be engaging. The engine is LOUD on the freeway at cruising speed, and pushing the OD on/off button does nothing. The button does light up as though it's toggling, but it has no effect on engine noise at all. This tub has no tach so I can't verify RPMs, but I think we can all agree you should hear the difference between 3rd and OD. There are no new engine codes after this issue started.

My research brought me to several threads on this and other forums, wherein people have the same issue and are told to put a switch on the OD solenoid to control it manually. This interests me greatly as a quick fix, as I'm taking a fairly long road trip in a couple weeks and do not have time to dick around with replacing sensors and everything down the list. However, I'm not finding it as simple as it's been suggested to be.

People seem to agree that the OD solenoid plug is on the driver's side of the trans, situated vertically, with two wires. The only diagram I can find has it located here:



However, that plug on my van has three wires:



This complicates "put a switch on the orange wire and hook the other end of the switch to ground". Probing with a multimeter, key on engine off, I get 12v from the center wire to BOTH orange wires. Unplugging this thing gives me code 37 and 45; 37 is "unexpected output from OD solenoid" and 45 is "temp sensor voltage out of bounds". So this DOES control the OD solenoid if anything does, right?

I'm at the end of my wits with this. My Haynes book doesn't even mention this thing other than that it exists. Can anyone point me in any kind of a direction as to how to proceed with this repair? My priority is getting it working first (1800 mile drive in a couple weeks, I absolutely cannot do it in 3rd gear) and diagnosing the root cause later. However, if there are any inexpensive/easy sensors to replace, THAT I will happily try.

 

Three wires there, power feed, and grounds for TCC, and O/D solenoids. Put the switch in the ground circuit for the O/D solenoid, and just run it to a good ground. Flip the switch, O/D engages.

 

How do I figure out which is which? I think I need to switch both, since whatever sensor is disabling the OD solenoid probably controls the lockup, too. But I don't think switching the wrong one at the wrong speed is a good idea..

 

Need wiring diagrams to see which is which. Both black wires control solenoids. TCC, and O/D. Getting the wrong one will be readily apparent, as the RPM drop will be pretty small.

 

"Both black wires" - There's one black (maybe dark blue, I can't tell, it's filthy) and two orange (one MAY be orange/black, but again, filthy)

TCC is the lockup, correct?

 

Correct. One wire will be 12 volt supply. You wanna play with one of the other two.

 

OK!

I'd like to understand a little more here before I go cutting wires. I'm getting 12v from the center wire, with both orange wires having continuity to ground. (IE I get 12v from center to each orange wire)

I understand the solenoids are always getting 12v from the battery, and they're switched on the GROUND side. Should that switch be closed with the engine off? Seems like the opposite.. Or does it energize it with the engine off to get a reading off the things or something?

Pardon my questions, I just really prefer to have a full picture in my head of how what I'm doing affects the systems I'm hacking into. Thanks for the replies!

Edit: Also, what kind of amps might I expect these solenoids to consume? So I know what grade of switches to buy for this.

 

The grounds should be normally open..... computer provides ground path for the circuits. If you are actually seeing a ground with trans in park, something is awry. If you are testing for voltage at each wire, with the other probe grounded somewhere, that is ok.

It's just a solenoid, so, I don't think they are real high amperage. I figger a 10 amp switch should be adequate to the task.

 

I had my mult in voltage mode, red probe on the center terminal in the plug. Touching the black probe to the terminals on either side gave me 12v. This was key on, engine off.

 

That shouldn't be happening...... Wonder if the solenoids are bad...... but, where they are grounding out, I have no idea.