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I think that since you got the OD light to light you are past the first gear switch - so I think that switch is good. The problem now is that the OD light does not light if you put the OD relay back in. This would indicate:
1. A bad OD relay.
2. Something that the ECM sees, like engine temp, is preventing it from energizing the relay. I know you got the engine up to 190 but I believe that the ECM sees a different sensor than the LCD gauge does so it could be getting the wrong reading. If you could connect a scan tool to the car you could verify the engine temp reading.
3. The ECM wants to energize the relay but it's connection to ground is bad or the "switch" inside the ECM which connects the relay to ground is bad.
I think the goal right now should be to get the OD light to light while you are driving. You should look over the troubleshooting charts in the FSM.
Alternately you could jump +12v power to ALDL pin F which would light the light and energize the OD solenoid as long as the OD relay controller by the ECM does not energize. Ray Quayle who posted the colored diagram expressed some doubt as to whether its really pin F so you should check the wire color like he said. This might get the OD to work but would not solve the real problem.
I think that the replacement of the 2nd & 4th gear switches would help give the ECM the inputs it needs to make it decide to energize the OD but I don't know if not having the 2nd and 4th switches would necessarily keep the ECM from energizing it.
So now I think he needs to see if the ECM wants to energize the OD. I don't know if a scan tool will show that but it would be nice if it did. I guess his next step is to see if the ECM has all the conditions on its inputs (engine temp, etc.) so that it should try to energize the OD.
Got the car back from the Chevy dealer, here's what they did:
Replaced the 1st, 2nd & 4th gear OD "switches". (they said the original ones did not OHM correctly).
They tested the OD wiring going into the ECM, and that all tested good.
There was a ground problem, going from the OD "B" relay to the ECM, so they installed a new ground at the OD "B" relay at the firewall, they tested all of the other OD components, and they all tested good.
The OD is now working, bypassing the ECM, so I do not have worry about the coolant temp @ 180*+ or the speed sensor at 25 MPH +.
Again "many" thanks for your continued support.
I hope these postings will help others in the future . . .
A few things to keep in mind, I spent several hours with the help of this forum to try to resolve or pin point the problems. With this 4+3 overdrive, there's at least 18 points of failure, so I was able to test about 12 of them without raising the car off the ground - plus I have already removed the dash panels, replaced the OD relay and tested several components.
When I took it to the Chevy dealership, and asked them if they have experience with the 4+3 manual trans with overdrive, the "mechanics" told me they had not seen one of these for 30 years, and they had no access to manuals - so I gave them my manual(s) and the OD wiring diagram (huge help) which was graciously provided from the forum.
The car was at the Dealer for 2 weeks, of which they had to order the 1st gear switch, which took 3 days to deliver, as Chevy no longer makes this part, then they had to order the 2nd & 4th gear switch, which took 2 days to deliver, then install test.
In addition, I had them service the OD unit, cleaning the OD filter and fresh oil, then seal the OD unit.
They also had to add a ground wire from OD relay terminal "B" in order for the OD to work, bypassing the ECM - (all the ECM connections were good).
Total bill was $405, plus I tipped the mechanic. With the help of this forum, I was able to suggest several things to try to the Chevy tech, of which he called me 3 times to ask me my thoughts on additional tests.
Again, "many" thanks to those who posted positive comments . . .
I am glad you got it worked out. You got a lot of valuable work done for that amount of money. You will like the ECM bypass, one of the best mods I have done to my car. Get a Hurst pistol grip handle, You will love it!
Wow. This looked like an ordeal. I just fixed my no-OD condition and it was a breeze. I thought I'd add to this tread for the future victims.
The '84 OD relay connects 12V to the solenoid with only the 1st gear switch, dash switch, and the pressure switch able to break the connection (and in that order). The "Overdrive Engaged" light is between the dash switch and the solenoid so if it comes on you know you've got continuity at least through the switch.
First thing to do is open the relay casing and close the points manually with a wedge. Then, turn on the ignition and flip the dash switch. If "Overdrive Engaged" comes on the problem is the few inches of wire from the dash switch to the OD connector on the OD case, or something in inside the case (pressure switch, solenoid itself, etc.)
In my case, the dash switch was not working. After some rapid flipping "Overdrive Engaged" started to flicker. WD-40 does a great job of reviving old mechanical electrical contacts. It was originally designed for driving water out of circuits after all (Water Dispersant, formula #40). The switch has two openings on either side where you can see the contacts sliding. A drop in each and "Overdrive Engaged" comes on solidly now.
As for diagnosing the dash switch, I saw some comments about pulling it to test it isolated. You can't do that with mine because there are no quick disconnects. The wires are crimped into metal posts which are riveted to the bottom of the switch. Instead, I jumped the two connector posts with an alligator clip test lead. The "Overdrive Engaged" light came on so I knew it was the switch. *whew* (easy fix)
As for getting at the switch, the bezels are setup so that they interlock. The IP bezel comes out first, then the one around the HVAC controls, then the shifter panel bezel. However, you can get just the shifter panel bezel up "enough" at the rear end to use a long phillips head to remove the switch screws. Don't drop a screw or (you guessed it) you're screwed. Taking all the bezels out only takes 5 minutes. The main hassle is having to get the driver's door all the way open to access the 3 screws on the side. The danger is that you'll hit the IP face with a tool (or knuckle) and break an LCD panel. Then you'll need to contact AER Technologies for a rebuilt one (http://www.aertech.com/dealers/make-gm.asp). I've been to their shop twice. So, beware. *laugh* Now, I have a fitted sheet of cardboard that I cover the IP face with anytime I'm working near it.
I'm attaching a clearer copy of the factory service manual addendum which covers this. Also, a shot of the troubleshooting section of the main manual.
Connector "B" goes to the "overdrive relay control" pin on the ECM. While the output is "low" when active, it's not a chassis ground. Grounding connector "B" is OK, will make the OD fully manual, and is equivalent to wedging the relay closed. However, one should not chassis-ground the "overdrive relay control" pin on the ECM itself. Might not hurt anything but the relay coil's impedance may be necessary to protect that particular ECM output. Since grounding relay pin "B" solved your car's problem, either the wire from "B" to the ECM is bad or that output on the ECM is bad.
A note on the relay, it's a standard GM fuel pump relay. Mine quit (coil looks overheated) and I got a replacement here cheap. (
The curious thing about this diagram is that the pressure switch is missing. Given it's mentioned in the trouble shooting list below, I assume it's really in there.
Glad you were able to resolve and fix your OD problems . . .
There's a lot of good info & people on this forum.
Originally Posted by ZPM
Wow. This looked like an ordeal. I just fixed my no-OD condition and it was a breeze. I thought I'd add to this tread for the future victims.
The '84 OD relay connects 12V to the solenoid with only the 1st gear switch, dash switch, and the pressure switch able to break the connection (and in that order). The "Overdrive Engaged" light is between the dash switch and the solenoid so if it comes on you know you've got continuity at least through the switch.
First thing to do is open the relay casing and close the points manually with a wedge. Then, turn on the ignition and flip the dash switch. If "Overdrive Engaged" comes on the problem is the few inches of wire from the dash switch to the OD connector on the OD case, or something in inside the case (pressure switch, solenoid itself, etc.)
In my case, the dash switch was not working. After some rapid flipping "Overdrive Engaged" started to flicker. WD-40 does a great job of reviving old mechanical electrical contacts. It was originally designed for driving water out of circuits after all (Water Dispersant, formula #40). The switch has two openings on either side where you can see the contacts sliding. A drop in each and "Overdrive Engaged" comes on solidly now.
As for diagnosing the dash switch, I saw some comments about pulling it to test it isolated. You can't do that with mine because there are no quick disconnects. The wires are crimped into metal posts which are riveted to the bottom of the switch. Instead, I jumped the two connector posts with an alligator clip test lead. The "Overdrive Engaged" light came on so I knew it was the switch. *whew* (easy fix)
As for getting at the switch, the bezels are setup so that they interlock. The IP bezel comes out first, then the one around the HVAC controls, then the shifter panel bezel. However, you can get just the shifter panel bezel up "enough" at the rear end to use a long phillips head to remove the switch screws. Don't drop a screw or (you guessed it) you're screwed. Taking all the bezels out only takes 5 minutes. The main hassle is having to get the driver's door all the way open to access the 3 screws on the side. The danger is that you'll hit the IP face with a tool (or knuckle) and break an LCD panel. Then you'll need to contact AER Technologies for a rebuilt one (http://www.aertech.com/dealers/make-gm.asp). I've been to their shop twice. So, beware. *laugh* Now, I have a fitted sheet of cardboard that I cover the IP face with anytime I'm working near it.
I'm attaching a clearer copy of the factory service manual addendum which covers this. Also, a shot of the troubleshooting section of the main manual.
Connector "B" goes to the "overdrive relay control" pin on the ECM. While the output is "low" when active, it's not a chassis ground. Grounding connector "B" is OK, will make the OD fully manual, and is equivalent to wedging the relay closed. However, one should not chassis-ground the "overdrive relay control" pin on the ECM itself. Might not hurt anything but the relay coil's impedance may be necessary to protect that particular ECM output. Since grounding relay pin "B" solved your car's problem, either the wire from "B" to the ECM is bad or that output on the ECM is bad.
The curious thing about this diagram is that the pressure switch is missing. Given it's mentioned in the trouble shooting list below, I assume it's really in there.
