85 - 4+3 Tranny troublehooting help - electrical

[XQIZT]

This is possibly related to the "missing" problem I am having.

The car STILL periodically bucks/misses/slips at about 70mph with the OD engaged in 4th gear. Enough so that I don't want to drive the car for fear of it stranding me.

I'm trying to hunt this down (now with the help of professionals) and I do not want to pay for "guesses." Fixing a problem is fine, shooting in the dark is a waste of money.

So what is the electrical set up for the OD's? There's the switch (mine in on the console, not in the shifter). There's the light in the DIC. There's the relay on the firewall next to the fuel pump relay. There is the OD itself (which is a rebuild unit from SK Speed, only about 40K miles on it or so, all proper maintenance done).

I'd like to try and test on bit at a time, either by bypassing it or whatever, in an attempt to track down the faulty part.

Monday its going to get driven with a diagnostic computer hooked up, so that we can see if the OD is being "ordered" off by the computer, and then almost instantly "ordered" back on. The "engaged" light never flickers off when this problem occurs, and its so fast that I don't hear a difference in RPM either.

Any thoughts, ideas, questions, suggestions, etc...please...they're all welcome!

[walleyfisher]

I was sitting back and waiting for some response. sorry that I'm your first.

Our '84 OD has worked flawless so far. (It’s a little slow at engaging after sitting for 3 months though)

Being I have had not to fix anything on the trans except for the shift position switches and fluid change

I would have to come to the conclusion that if your OD is engaging after the motor is up to temp and the computer determined that the RPM are high enough, that if you are experiencing it dropping out intermittently I would have a couple of guesses:

There are (5) screw in switches that inform the CPU which gear the car is in. If you look there are (2) on each of the shift levers and (1) on the reverse lever on the transmission.

These switches get corroded and greasy and are have known for failure. I would try swapping the 4th gear switch with maybe the reverse and see if the problem goes away. Also when you have it out, look for wear on the ball, maybe there is not enough "detent" on the shaft to operate the switch.

The other thing check for bad wiring to temp sensor for computer (not the gauge) If memory serves me right, the temp sensor for the computer is the one above the water pump below the air pump.

[XQIZT]

Wally thanks. Its getting maddening at this point!! I'll look into what you suggested.

Engine wise, the ZZ4 motor purrs...and pulls until I say stop basically. Timing is dead on. Re-checked and still dead on (at a suggested 10*BTDC). New cap, rotor, coil, ignition module, plugs, OD relay. Wires ohm out to spec, as do the injectors. Fuel pressure hits the mark at like 39PSI and is rock solid. Fluids are at the correct level. I cleaned the IAC. EGR deleted (and no codes). Ran Seafoam through the tank per can instructions. No vac leaks that I can find.

And its not like this "miss" (or whatever) is long...its a quick BLIP. Then everything returns to normal.

[wildcatlock]

Originally Posted by walleyfisher

I was sitting back and waiting for some response. sorry that I'm your first.

Our '84 OD has worked flawless so far. (It’s a little slow at engaging after sitting for 3 months though)

Being I have had not to fix anything on the trans except for the shift position switches and fluid change

I would have to come to the conclusion that if your OD is engaging after the motor is up to temp and the computer determined that the RPM are high enough, that if you are experiencing it dropping out intermittently I would have a couple of guesses:

There are (5) screw in switches that inform the CPU which gear the car is in. If you look there are (2) on each of the shift levers and (1) on the reverse lever on the transmission.

These switches get corroded and greasy and are have known for failure. I would try swapping the 4th gear switch with maybe the reverse and see if the problem goes away. Also when you have it out, look for wear on the ball, maybe there is not enough "detent" on the shaft to operate the switch.

The other thing check for bad wiring to temp sensor for computer (not the gauge) If memory serves me right, the temp sensor for the computer is the one above the water pump below the air pump.

With everything else you have checked and all the suggestions I made ( no help there ) I had forgotten about the switches. That is about the only thing left. BTW you still have your CF top? How is it holding up? Considering getting one from socali. Cant believe you are still fighting these issues. Thought you had it fixed/figured out. Hopefully the datalog will show something. Good to hear you havent given up though.

[vetteoz]

Originally Posted by XQIZT

So what is the electrical set up for the OD's?
There's the switch
There's the light in the DIC.
There's the relay There is the OD itself
I'd like to try and test on bit at a time, either by bypassing it or whatever, in an attempt to track down the faulty part.

Power goes from relay through 1st gear lockout switch to the solenoid. The relay is controlled by the ECM.

Switch allows you to have man or auto control of the O/d
Light only shows power coming out of the relay; not indication that the O/d is receiving power or is engaged,
There is no feedback other than change of revs to indicate O/d is engaged (or not )

Can you manually engage the O/d?
Before driving off , put O/d button in Off , drive to get up to O/d Min op temp ( 140 F in your car ) and see if you can engage the O/d by pushing the button.
If you can ,you know all components are working because the switch sends a signal to the ECM which then operates the relay

[vetteoz]

Originally Posted by XQIZT

so that we can see if the OD is being "ordered" off by the computer, and then almost instantly "ordered" back on.

If your problem truly is the rapid engage / disengage of the o/d I doubt that is happening ,
more likely to be a "physical problem" like a loose / bad connection somewhere dropping the power out.
What does the relay connector look like?
Not uncommon to have problems there on the early style relays ; the bare wires can short to each other doing weird things

Edit
If you think the ECM is screwing with the O/d , you could put 12V to terminal F on the ALDL connector ( while driving )
and that would engage the O/d full time, bypassing the ECM controlled relay assuming your wiring is sound ( ref above )

[vetteoz]

Diagram for '86 O/d control.
Only major difference I am aware of is your car has a "Off /On " switch on the control line to the ECM where as later cars have the " momentary contact" switch as shown below

Not shown is the 1st gear lockout switch which would be on wire #901 (dk green ) between the relay terminal A and the terminal on the side of the O/d.
'86 was only year not to have that switch