I should know the answer but.....

[nyernga]

Here's the question and it involves the infamous 4+3 trannmission. When I first begin driving and the car reaches 124 degrees I hit the OD button. The OD light comes on but the unit doesn't engage. After about 20 minutes or so of driving, it starts working just fine. So, with the indicator light coming on I know the switch works ok. The question is.............Relay? And if so, the manual shows the relay on the firewall alongside another one. The problem is there are no relays at that location on my car. I do however, have two relays mounted to the back of the drivers side wheel well that are unaccounted for.

Any thoughts???????

Len

 

[rrubel]

You should have a 4+3 relay *and* a fuel-pump relay next to the washer motor. They should be mounted one on top of the other, and they're identical so it's not easy to tell which is which (you need to check the wire colors, which are all black... at least after 15+ years ). If you do have them, just swap the relays.

Also, the plastic around the wires is notorious for shrinking with age/heat and allowing the wires to touch and short. My fuel pump stopped working for this reason...

[RICHR]

 

[nyernga]

You should have a 4+3 relay *and* a fuel-pump relay next to the washer motor. They should be mounted one on top of the other, and they're identical so it's not easy to tell which is which (you need to check the wire colors, which are all black... at least after 15+ years ). If you do have them, just swap the relays.

Also, the plastic around the wires is notorious for shrinking with age/heat and allowing the wires to touch and short. My fuel pump stopped working for this reason...

[RICHR]

Thanks Rich. My service manual and the alldata website both show the relays on the firewall by the brake booster. The problem is the only "double" relays there are the MAF power and MAF burnoff relays. There is a single next to the washer motor. I must be the only one with relays mounted to the rear of the drivers wheel well. Wire color matching may be the only answer.
I did read about what controls the OD unit and there may be a problem with the internal pressure switch or solenoid. I'm hoping it's just the relay. I can eliminate some things like the fuse, shifter switch, temp sensor because they would not necessarily work intermittently. I'll pick up a relay at pep-boys and pop it in..... well as soon as I figure out where the darn relay is...

Len

 

[MoeJr]

I would bet that the computer will not allow the trans to go into OD until much warmer than 124 degrees. I am thinkg about 160 or so. Just my .02

 

[WhalePirot]

The 4+3 is a GREAT unit, if maligned, unjustly

Rich is right on: swapping plugs on the relays, then checking for fuel pump operation is the easiest. My relays were originally on the firewall, too, but I moved them both, when I moved the battery. They joined the fan relay, as neighbors.

I bought a ($12; Chinese made) new relay from Chevy, which now sits unused, as I just solved a problem like yours. Mine turned out to be the 3 & 4 gear linkage switch. Turning the switch 'on' (+12vdc) sends a 'request' for O/D to the ECM and turns on the dash light, but the ECM won't allow O/D until closed loop ops. This is not, strictly speaking, triggered by a temperature switch.

The dash light coming on means the +12vdc side is okay, at least to the linkage switch(es). The pressure switch is inside the Nash, and not directly testable w/o dropping the pan. The external lug is merely a pass-thru, and not of too much value when troubleshooting, except that the +12vdc can be found, if the switches and relay are okay and operating, i.e. sending the voltage there.

The other half of this circuit, the GND side is controlled by the ECM (as above), again, though the relay.

If the late O/D 'on' is occurring in a consistant manner, it may not be a problem with the relay's contacts, which can be 'dressed' up, with emery cloth and contact cleaner, after the cover is removed.

Please check for proper fluid level in the Nash, especially if the unit cycles, particularly under lateral/longitudinal G's. Years ago, before any serious mods, I fixed a cyclic O/D by changing spark plug wires. Honest, I did nothing else! While the unit used to 'come on' exactly at 174* temperature, that trigger temperature had raised significantly; then became cyclic, even at steady, freeway speeds. The wire change restored the original operation.

FWIW, I believe that my mods and perhaps weak wires had caused a rich condition, which was sensed by the oxygen sensor, thereby, the ECM said "Open Loop" >no O/D. My tailpipes were blackish, too.

There have also been reports here, of problems with the console switch. It switches the 12vdc that it is fed.

 

[nyernga]

Rich is right on: swapping plugs on the relays, then checking for fuel pump operation is the easiest. My relays were originally on the firewall, too, but I moved them both, when I moved the battery. They joined the fan relay, as neighbors.

I bought a ($12; Chinese made) new relay from Chevy, which now sits unused, as I just solved a problem like yours. Mine turned out to be the 3 & 4 gear linkage switch. Turning the switch 'on' (+12vdc) sends a 'request' for O/D to the ECM and turns on the dash light, but the ECM won't allow O/D until closed loop ops. This is not, strictly speaking, triggered by a temperature switch.

The dash light coming on means the +12vdc side is okay, at least to the linkage switch(es). The pressure switch is inside the Nash, and not directly testable w/o dropping the pan. The external lug is merely a pass-thru, and not of too much value when troubleshooting, except that the +12vdc can be found, if the switches and relay are okay and operating, i.e. sending the voltage there.

The other half of this circuit, the GND side is controlled by the ECM (as above), again, though the relay.

If the late O/D 'on' is occurring in a consistant manner, it may not be a problem with the relay's contacts, which can be 'dressed' up, with emery cloth and contact cleaner, after the cover is removed.

Please check for proper fluid level in the Nash, especially if the unit cycles, particularly under lateral/longitudinal G's. Years ago, before any serious mods, I fixed a cyclic O/D by changing spark plug wires. Honest, I did nothing else! While the unit used to 'come on' exactly at 174* temperature, that trigger temperature had raised significantly; then became cyclic, even at steady, freeway speeds. The wire change restored the original operation.

FWIW, I believe that my mods and perhaps weak wires had caused a rich condition, which was sensed by the oxygen sensor, thereby, the ECM said "Open Loop" >no O/D. My tailpipes were blackish, too.

There have also been reports here, of problems with the console switch. It switches the 12vdc that it is fed.

Thanks whale. I was thinking the same thing about the relay. Usually they either fail or work. Unless of course the signal going to them is erratic. I'll pick up a relay and pop it in. If nothing else I'll have a spare for future use.
I had the fluid and filter changed about 7 months ago. Very little mileage since then as the car sits in the garage during the week. Reading your comment about an "open loop" condition sounds like a good place to start. My plug wires are almost 4 1/2 years old. Looks like I'll be busy this weekend.

Len

ps: I love the 4+3 by the way.........no real problems since I bought the car 5 years ago.

 

[Silveradojoe]

I also have the 4+3 and my OD stopped working a week ago. I figured the fluid could be low or need changing as I've read here before.
Driving this past weekend I experienced an occasional strange vibration as I slowed down to stop in 2nd or 3rd gear. It felt like driving overthose rumblestrips approaching a highway toll plaza. At one point I thought the engine was about to stall out. I disengaged the OD for the rest of the day and the vibration did not happen again decelerating to a stop.
Can the strange vibration and OD problem be related? Any help would be appreciated.
Joe

 

[WhalePirot]

Can the strange vibration and OD problem be related?

Assuming you had the O/D on when the shuddering occurred, yes. My guess is that the clutches were trying to keep it in O/D, but had insufficient pressure to hold. I will not claim to be an expert on these things, but I have messed around with the outside.

It is a great unit, if unique; therefore draws some fire.

 

[Silveradojoe]

Whalepirot,
Thanks for your input. Yes, the OD switch was on, even though it wasn't working. I agree with you and hope that the problem disappears after the OD unit is working properly again.
Joe

 

[WhalePirot]

YW. Don't drive too long if you think the fluid is low.