4+3 Problems in Paradise Miami, Fla.

wetwolf · 05-27-04, 06:10 PM

I have a 1985 Vette with a 4+3 and 130,000 Miles,the engine is strong and smooth. My over drive in the other hand is working backward than it is suppose to. When cool and at low speed the over drive is in gear. At speed over 55mph
it shift into striaght drive. I have code 15 that is the cooling temp sensor and it was replace, I also replace the O-D relay and the problem was not fix.
If some one knows of a way to fix it or a way to bypass the computer in order to regain control please tell me.

**corvette66** · 05-27-04, 10:59 PM

Oh man them Overdrives really stink. I rebuilt mine once, and have had it apart probaly 4 times. It is really hard to locate a problem with them.

What exactly is it doing at 55mph?

Does it slip out of gear at 55? You say it stays in overdrive when you run at low speeds, What happens when you shift into 4th and the overdrive is already engaged? Does it jump out? Or what happens when you shift into 4th then hit the OD switch?

**WhalePirot** · 05-29-04, 09:08 PM

Has this problem just begun? Did the code appear at the same time?

The relay was NOT the issue, as you found, because the O/D was beinig switched on and off by it. The dash light would indicate the same, even if the O/D did not actually engage.

The ECM controls the availability of the overdrive and requires the engine to be in closed loop. Part of the criteria for closed loop (the engine is taking sensor input and controlling based upon the inputs) is engine temperature.

Some owners run a 12v wire directly from the switch to the relay, bypassing the ECM. The relay has wires for: battery-12v /control 12v/ Ground/ wire to O/D solenoid. The direct wire replaces the ECM (control) wire on the relay.

wetwolf · 06-16-04, 03:41 PM

Originally Posted by corvette66

Oh man them Overdrives really stink. I rebuilt mine once, and have had it apart probaly 4 times. It is really hard to locate a problem with them.

What exactly is it doing at 55mph?

Does it slip out of gear at 55? You say it stays in overdrive when you run at low speeds, What happens when you shift into 4th and the overdrive is already engaged? Does it jump out? Or what happens when you shift into 4th then hit the OD switch?

nothin

At 55 mph jump back to strait drive, the overdrive bottom on the shifter dont work. I can push that bottom & nothin hapen.

wetwolf · 06-16-04, 04:00 PM

I like the idea of baypasing the computer but I did't understand your explanation .
Please can you expand . Thank.
The overdrive switch on the shifter looks kind of week to connect 12V , if you can explain step by step Y can fallow instruction well also I like to hear more about your
Viper eating Corvette

**trupp** · 06-21-04, 03:18 PM

I would check the fluid level on the od unit and make sure you have sufficient transmission fluid it sounds like you might be low on fluid.

wetwolf · 06-21-04, 05:12 PM

Originally Posted by trupp

I would check the fluid level on the od unit and make sure you have sufficient transmission fluid it sounds like you might be low on fluid.

Dear Trupp
The first thin I check was the fluid & the od was ok but the trany was low so I
add olmost a quart of 90sae oil

wetwolf · 06-21-04, 05:33 PM

Wetwolf Thank you WhalePirot I ran an experiment base on your comment.
I connected a 12v line directly on to the electrical connector on the driver side of the OD and the OD is on all the time, it does't slip any more and that shows me that the OD is in good working order. Now I'm going to connect the OD baypassing the ECM your way.
Wetwolf.

**WhalePirot** · 06-21-04, 09:35 PM

Sorry for the delay; been away, fishing for the halibut.

I do not know exactly how to wire it, as mine was done by a shop. I would connect the 12vdc supply to the switch you use and the other side of the switch to the O/D relay, under the hood.

There are two identical relays and it sounds like yours are okay. You also know the solenoid at the O/D unit checks out okay. The other relay triggers the fuel pump, so pulling the connector from one will tell you which it is, if the car starts or will not start. (You could just check for fuel pressure.)

I would check the following against the wiring diagram, as it is from memory: There are five wires on the relay. The end, red wire is hot all the time; the next red wire is switched; one is ground and one outputs to the O/D. I do not recall, at the moment what the fifth is for. The 'second', switched wire should feed from the switch you utilize. All else is unchanged.