What signal does an auto trans need to work properly?

[Mike7447]

I am going to add a MS pro ecu to control the engine and FP. If I install  the new ecu in piggy back style, and leave the factory ecu in place, what signal will the trans need to work properly? I.e. rpm? 

 

Edited April 29 by Mike7447

[psu_Crash]

Sounds like you are running fuel only on the MS. That won't effect the trans. I'm not well versed on the autos though. I'm sure someone else will chime in. 

[Mike7447]

53 minutes ago, psu_Crash said:

Sounds like you are running fuel only on the MS. That won't effect the trans. I'm not well versed on the autos though. I'm sure someone else will chime in. 

Nope, I’m gonna run fuel and spark. I don’t want to lose any functionality, only seeking to improve the way it runs. 
I purchased a MS3pro mini. It’ll go way beyond what I want to do with this project, to include control of the auto w/the purchase of an additional controller.

Right now though, the trans appears to have 3gears, plus O/D full time. The button on the shifter does nothing. 

[admin_JAinsworth]

Here is a write-up from Mike_C:

. The O/D is controlled by a relay; the relay has to be ON to allow O/D. The relay is turned ON by a combination of 2 things:
* O/D switch on the shift lever has to be in O/D enable/on position
* Temp sensor switch in engine coolant has to "see" some warmth in the coolant; O/D is disabled until the engine is warmed up a bit.

So what causes the problems? Typically a combination of two things:
1: Temp sensor going bad - it's supposed to be an ON/OFF switch but when it ages it builds up resistance in the ON position. That starves the relay of working voltage.
2: poor wiring/connectors/fusible links in the IGN circuit. The IGN circuit powers EVERYTHING turned on/off by the ignition key. Bad connections rob voltage in this circuit... This circuit feeds your dash guages, the turn signals, and the O/D relay among other things. Ever notice how your voltmeter "dances" in sync with the high-amperage turn signals? You're seeing the effects of long, old wires, bad connections, etc.

To fix:
1: disconnect the battery for safety, key OUT of the ignition
2: In the fusible link box (those wire loops between the battery and ignition coil) remove the links one by one. Clean the contacts on the box and on the link. Test each link with an ohmmeter; if they show more than a couple tenths of an ohm resistance replace that link with a dealer part. They're not expensive and will cure LOTS of problems.
3: Follow the wires to/from the fusible link box to some connectors in that area. Undo them one by one and clean them as well. Auto parts stores sell a spray electrical parts cleaner that works well. Don't use spray carb or brake cleaner... they'll disolve the plastic connectors.

4: check or just replace the temp sensor. Look for a temp sensor with a yellow+green wire feeding it. On the 87-later cars it'll be near the thermostat housing. Probably the same for earlier cars but I don't know for sure. To test the sensor: warm up the engine, then shut it down. Disconnect the wire going to the sensor. If the tang is loose or twists around, the sensor has disintegrated and is shot. Otherwise, use an ohmmeter to probe from the threaded nut portion of the sensor to the tang; it should read zero ohms. I'll bet yours reads several ohms. Drain a little coolant out of the system before removing the sensor!

As a short-term workaround, you can unplug the sensor connector and just ground the wire. That'll enable O/D at all times - warm or cold engine. Use the switch on the shift lever to disable O/D until the engine warms up a bit.

mike c.

[Mike7447]

2 hours ago, admin_JAinsworth said:

Here is a write-up from Mike_C:

. The O/D is controlled by a relay; the relay has to be ON to allow O/D. The relay is turned ON by a combination of 2 things:
* O/D switch on the shift lever has to be in O/D enable/on position
* Temp sensor switch in engine coolant has to "see" some warmth in the coolant; O/D is disabled until the engine is warmed up a bit.

So what causes the problems? Typically a combination of two things:
1: Temp sensor going bad - it's supposed to be an ON/OFF switch but when it ages it builds up resistance in the ON position. That starves the relay of working voltage.
2: poor wiring/connectors/fusible links in the IGN circuit. The IGN circuit powers EVERYTHING turned on/off by the ignition key. Bad connections rob voltage in this circuit... This circuit feeds your dash guages, the turn signals, and the O/D relay among other things. Ever notice how your voltmeter "dances" in sync with the high-amperage turn signals? You're seeing the effects of long, old wires, bad connections, etc.

To fix:
1: disconnect the battery for safety, key OUT of the ignition
2: In the fusible link box (those wire loops between the battery and ignition coil) remove the links one by one. Clean the contacts on the box and on the link. Test each link with an ohmmeter; if they show more than a couple tenths of an ohm resistance replace that link with a dealer part. They're not expensive and will cure LOTS of problems.
3: Follow the wires to/from the fusible link box to some connectors in that area. Undo them one by one and clean them as well. Auto parts stores sell a spray electrical parts cleaner that works well. Don't use spray carb or brake cleaner... they'll disolve the plastic connectors.

4: check or just replace the temp sensor. Look for a temp sensor with a yellow+green wire feeding it. On the 87-later cars it'll be near the thermostat housing. Probably the same for earlier cars but I don't know for sure. To test the sensor: warm up the engine, then shut it down. Disconnect the wire going to the sensor. If the tang is loose or twists around, the sensor has disintegrated and is shot. Otherwise, use an ohmmeter to probe from the threaded nut portion of the sensor to the tang; it should read zero ohms. I'll bet yours reads several ohms. Drain a little coolant out of the system before removing the sensor!

As a short-term workaround, you can unplug the sensor connector and just ground the wire. That'll enable O/D at all times - warm or cold engine. Use the switch on the shift lever to disable O/D until the engine warms up a bit.

mike c.

Thanks for that, I really appreciate it. Is the OD circuit the only thing that the transmission reads electronically via related sensors to work? I think I read that there is a vacuum modulator in the thing… meaning that other than OD, it’s a standard 3 speed trans. And if that’s the case, what did the factory do to block boost from pressuring the modulator?