Even with a cooler thermostat, your temp shouldn't drop that low. Replace it.
4+3 Overdrive ECM Bypass
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Joined: Oct 2013
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From: Atascadero CA
4+3 Overdrive ECM Bypass
Ok, so I finally got my 4+3 OD unit replaced and it is working correctly. However, since it is winter, I frequently am driving on the freeway and my coolant temp will drop below 140 and the OD will kick off, then heat back up and kick back on, cool back down and so on. It's really annoying, so I would like to bypass the ECM and have manual control.
I have a 1985 early with the Overdrive switch on the console. I took apart the passenger kick panel to get to the ECM but there was no way in hell I was going to be able to get it out past all of the wires.
So my next option that I've heard is to ground a wire from the OD relay. First question, haha, Where is the OD relay!? What I've gathered, is you typically cut the wire going to the B terminal, run the cut wire to a switch in the cab, then from the switch to ground.
Second question, since mine has the constant on/off switch already on the console, do I just need to ground the B Terminal wire with no switch, and use mine like normal?
Is this the best way to accomplish what I need (manual control of OD not dictated by engine temp)? Thank you for the advice!
I have a 1985 early with the Overdrive switch on the console. I took apart the passenger kick panel to get to the ECM but there was no way in hell I was going to be able to get it out past all of the wires.
So my next option that I've heard is to ground a wire from the OD relay. First question, haha, Where is the OD relay!? What I've gathered, is you typically cut the wire going to the B terminal, run the cut wire to a switch in the cab, then from the switch to ground.
Second question, since mine has the constant on/off switch already on the console, do I just need to ground the B Terminal wire with no switch, and use mine like normal?
Is this the best way to accomplish what I need (manual control of OD not dictated by engine temp)? Thank you for the advice!
Team Owner
Joined: Dec 1999
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
I think the real thing to do is to fix is the coolant temp problem. 140 degrees is far too cool for the engine.
What thermostat do you have? I have a 180 'stat in my '87 and the car will always maintain coolant temps between 178 and 210 depending on the weather and how I'm driving the car. I was out in the car a couple days ago with the air temp around 40 and the coolant temp stayed between 178 and 180 in both 25 MPH city driving and out on the freeway at 70 MPH.
The OD relay is on the firewall in front of the fuel pump relay. Both are next to the windshield wiper motor.
What thermostat do you have? I have a 180 'stat in my '87 and the car will always maintain coolant temps between 178 and 210 depending on the weather and how I'm driving the car. I was out in the car a couple days ago with the air temp around 40 and the coolant temp stayed between 178 and 180 in both 25 MPH city driving and out on the freeway at 70 MPH.
The OD relay is on the firewall in front of the fuel pump relay. Both are next to the windshield wiper motor.
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From: Atascadero CA
I think the real thing to do is to fix is the coolant temp problem. 140 degrees is far too cool for the engine.
What thermostat do you have? I have a 180 'stat in my '87 and the car will always maintain coolant temps between 178 and 210 depending on the weather and how I'm driving the car. I was out in the car a couple days ago with the air temp around 40 and the coolant temp stayed between 178 and 180 in both 25 MPH city driving and out on the freeway at 70 MPH.
The OD relay is on the firewall in front of the fuel pump relay. Both are next to the windshield wiper motor.
What thermostat do you have? I have a 180 'stat in my '87 and the car will always maintain coolant temps between 178 and 210 depending on the weather and how I'm driving the car. I was out in the car a couple days ago with the air temp around 40 and the coolant temp stayed between 178 and 180 in both 25 MPH city driving and out on the freeway at 70 MPH.
The OD relay is on the firewall in front of the fuel pump relay. Both are next to the windshield wiper motor.
Maybe the stat isn't closing all the way?
And thanks for the location, i figured it was one of the two.
Racer
Joined: Dec 2003
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Your 85 overdrive is designed to kick on at a minimum coolant temp of 140F, (84 mdl is 176) your first step should be to correct the low engine temp.
ps; if you have a fail safe stat it may be have failed in the open position. I have seen a number of them fail, get a standard thermostat.
ps; if you have a fail safe stat it may be have failed in the open position. I have seen a number of them fail, get a standard thermostat.
Last edited by frank j. moran; Nov 28, 2013 at 09:35 PM.
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Thread Starter
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Joined: Oct 2013
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From: Atascadero CA
Your 85 overdrive is designed to kick on at a minimum coolant temp of 140F, (84 mdl is 176) your first step should be to correct the low engine temp.
ps; if you have a fail safe stat it may be have failed in the open position. I have seen a number of them fail, get a standard thermostat.
I think i still want to bypass the ecm too, just for more control. Anyone have any insight on what to do with the relay?
Safety Car
Joined: Jan 2004
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If your setup is working correctly ,the O/d is always available when the programmed conditions ( inc engine temp ) are met unless you manually disengage it before driving off.
Cut the relay control wire ( tan /blk ?) to the ECM and run it to ground through a switch
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From: Atascadero CA
Race Director
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From: moraga ca
One of the first mods I made on my 84 when I bought it new 3 decades ago was to bypass the ECM and allow direct control of the overdrive using the overdrive switch on the console. It was relatively easy back then either grounding the switch wire to the of unit or supplying 12 volts. It's been a while. The do light on the dash still worked when the is was activated.
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From: Atascadero CA
One of the first mods I made on my 84 when I bought it new 3 decades ago was to bypass the ECM and allow direct control of the overdrive using the overdrive switch on the console. It was relatively easy back then either grounding the switch wire to the of unit or supplying 12 volts. It's been a while. The do light on the dash still worked when the is was activated.
Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
I don't have a schematic for an 85, but if my 86 switch was constant, I would cut the the wire from switch at ECM and cut the wire from ECM to relay and join them together beside ECM.
That would allow full control with no input from ECM.
Do you have a schematic for 85 OD ?
That would allow full control with no input from ECM.
Do you have a schematic for 85 OD ?
Race Director
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From: moraga ca
But am i correct in saying you didn't have to add another switch? I think that would only apply to the later years that had the momentary switch on the shifter, not for ours that have the constant switch on the console. I'm gonna give it a go tomorrow when i wake up from my food coma.
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From: Atascadero CA
https://wiki.bentleypublishers.com/d...g-1985%204.jpg
Can anyone confirm this? Last thing I want to do is damage the ECM by wiring something incorrectly.
Drifting
Joined: May 2006
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From: Chewelah Wa
When you bypass the ECM by running a ground switch to the relay, the switch (and you) essentially become the ECM. You just need to make sure that you cut or unhook the ECM wire from the relay. No risk of damage to anything. I do believe it is the "B" post on the relay. As far as the thermo, the fail safe will get stuck open. Mine did it several times until I cut the clips off that hold it open. I have an 85, and the ECM bypass is one of the best mods I have done to my car.
Last edited by powerpigz-51; Nov 29, 2013 at 05:42 PM.
Thread Starter
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Joined: Oct 2013
Posts: 73
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From: Atascadero CA
When you bypass the ECM by running a ground switch to the relay, the switch (and you) essentially become the ECM. You just need to make sure that you cut or unhook the ECM wire from the relay. No risk of damage to anything. I do believe it is the "B" post on the relay. As far as the thermo, the fail safe will get stuck open. Mine did it several times until I cut the clips off that hold it open. I have an 85, and the ECM bypass is one of the best mods I have done to my car.