1990 Mighty Max - Overdrive In/Out

[HHMM19]

I just had the transmission and ECM replaced and the overdrive still goes in and out. Sometimes it works, sometimes it doesn’t. All help much appreciated!

[HHMM19]

Also, if someone suggests that I ground a little black wire, please share the exact location (pic preferably) as pennyman has suggested this on every post.

[geezer101]

Hi and welcome to mightyram. The OD's are tripped by a temperature sensor on the engine so there could either be a problem with the sensor, a bad ground or the wiring to the sensor is sketchy. Bad grounds will cause random faults and charging issues so it's worth while disconnecting them and giving them a freshen up anyway. Maybe try grounding the temperature sensor to test the theory as well (once the engine is warm to avoid any risk of damaging the trans) Someone else will chime in and offer some insight.

[MrPaco]

The OD's are tripped by a temperature sensor on the engine

Geezer (or anyone else who knows about this stuff), can you explain how this works?
I just got a hold of an owner's manual, and here's what it has to say about OD (see the picture below).
If I'm reading this correctly, it's saying that the OD button, if pressed in (thus turning off the OD), it will only allow the A/T to go up to 3rd gear, but not 4th. If this is right, what role does the temperature sensor play on this?
Thanks, and I hope that question makes sense...

21537

[geezer101]

The temp sensor and related faults have come up from time to time. The above synopsis made by MrPaco is correct - there is a manual engage/disengage switch on the end of the control stalk. There are a bunch of components that could be the culprit like the manual switch assembly, the OD solenoid, the temp sensor etc. The temp sensor simply prevents OD from operating until the whole show has warmed up sufficiently.

[geezer101]

Could try flushing the OD button out with electrical contact cleaner - might be dirty contacts :shrug:

[BradMph]

I was thinking to hook a volt gauge to connectors and see if your getting intermittent connect disconnects at the same time that trany starts to play games. Almost sounds like a speed control relay or a broken solder spot. Our trucks are so old now, solder starts to give out on electrical.

[HHMM19]

Where is exactly is the temp sensor located? It seems that the overdrive works better when the truck is warm. If the truck does shift into overdrive, the button on the shifter does disengage. A picture would be super helpful. Location of Temp sensor, relay, wires to check. Thanks so much!

[Chargerx3]

Subscribed as well. My father has a 91 Ram 50 4x4 that will not go into OD. Someone replaced the motor at one point and im almost certain the proper intake manifold with the sensor are not there. When you cycle the column button the light will go on and off.

[pennyman1]

The temp sensor is located on the intake in front of the throttle body. it is a one terminal sensor. It delays the availability of o/d to when the truck is up to operating temperature. It is an emissions thing and is not necessary. There may be 2 sensors near each other in the same location - one is the gauge sensor and the other is the o/d sensor. both have black wires, but one should have a white tracer - that is the gauge sensor. There should be a spot on the intake beside the throttle body that has 1/4 inch lugs held on with a bolt - that is where to ground the sensor wire to give you o/d at any temperature. Hope this helps.

[Chargerx3]

The temp sensor is located on the intake in front of the throttle body. it is a one terminal sensor. It delays the availability of o/d to when the truck is up to operating temperature. It is an emissions thing and is not necessary. There may be 2 sensors near each other in the same location - one is the gauge sensor and the other is the o/d sensor. both have black wires, but one should have a white tracer - that is the gauge sensor. There should be a spot on the intake beside the throttle body that has 1/4 inch lugs held on with a bolt - that is where to ground the sensor wire to give you o/d at any temperature. Hope this helps.
Great explanation.

[Chargerx3]

Turns out that on the V6 the temp sensor is at the very front of the motor and that there are a total of 4 coolant temp sensors next to each other. I tried grounding both of the ones that were single leads to the battery but nothing changed. I’m going to try and ground at the TCU next just in case my wiring is bad. Any other suggestions?

[pennyman1]

you may have an transmission ECM that controls the o/d on your setup depending on the year of your transmission. Is this on the motor swapped truck?

[Chargerx3]

Correct it has an ECM. I tried jumping the lead coming out of it to ground and still no change. Wondering if the modual is bad. My luck it has leaky caps. Wonder if the 4 cyl TCU is the same or interchangeable with the V6?

[claych]

Honored Posters___
???4g67???
No matter,
Much more going on ,
https://ww2.justanswer.com/uploads/indytech/2012-07-21_122915_od.png

[Chargerx3]

That module looks to have the same amounts of leads and the same colors. Have a part number?

[claych]

Apologies Chargerx3 for the late reply,
TCU # MB670284.
---> obsolete<----

[Chargerx3]

Ok, so to summarize the V6 part number for the TCU is MB670284 and the 4Cyl is the SAME?

[claych]

MB670284,
Same for 4G64 & 6G72 from '91-'95
Verified on actual vehicles :shock:

[Chargerx3]

This opens up a new door for us V6 auto guys then. Albeit there are probably only a few hundred that ever existed but it means we aren’t stranded and can scalp from the red 4cyl trucks in the bone yard. Great work!

[claych]

I strive to be Tau'ri Colonel :)

[claych]

Update ,

MB670284 TCM
Same for 4G64 & 6G72 from '91-'95
2x4 or 4x4 !!!

Now verified on 3 vehicles.

[Chargerx3]

Update ,

MB670284 TCM
Same for 4G64 & 6G72 from '91-'95
2x4 or 4x4 !!!

Now verified on 3 vehicles.

Truth. Thanks to claych's extra 2wd TCM my fathers 4x4 V6 Ram is now shifting into OD. This is a great find for all us auto guys out here...2wd or 4wd.

Thanks bud!

[claych]

An Honor as always, Sir .

[Can1991Ram]

The OD is also sensitive the speed sensor in your Speedo. If your Speedometer is working incorrectly it will not go into OD. Probably not the case here but just adding that in.

While I waited for a new speedo cable I did the ole OD swap into an old Mopar trick and ran a toggle switch to ground and ran the other end to the proper line on the harness going into the tranny. When I wanted OD.. I would flip the switch grounding the wire and into OD it goes... but.... you have to flip the switch to go OUT of OD and remembering to do that can be a pain. Also this engages not only OD but the lock up IMMEDIATELY and can be jarring.

[claych]

Update:
Ck'd back on the module replacement...
Normal O/D & Lockup, repair verified & validated.

[claych]

Reed switch , not the issue here.
As to the rest ---
"Flip the switch" _________
& What of a panic stop where the need to steer & brake takes up all of
your synaptic 'time'?
Lockup, O/D, still engaged = stall on decel.

[geezer101]

Reed switch , not the issue here.
As to the rest ---
"Flip the switch" _________
& What of a panic stop where the need to steer & brake takes up all of
your synaptic 'time'?
Lockup, O/D, still engaged = stall on decel.

Trading one issue for another. Not having O/D won't get you killed but this is a sketchy ghetto fix - better to rectify the faulty O/D module as claych has done :thumbup: