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4+3 OD woes

Achilles

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Joined
Oct 31, 2004
Messages
447
Location
Back in Sunny California!
Corvette
1982 CE, 03 MY Z06
Suddenly had a problem lately with my overdrive not engaging on my 86. Tried switching the OD & FP relay to see if that was the culprit. Car didn't start after the switch. Conclusion...bad relay. So I removed the apparent faulty relay to get a new one and while driving the car to the parts store, it pops into OD. WTF? Can the OD work without the relay installed? It worked perfect in/out on comand. What gives?
 

wallyknoch

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Joined
Nov 9, 2002
Messages
457
Location
Dearborn
Corvette
One owner unrestored Black 1962 FI Corvette
You should service the 4+3 before it quits. Filter and new lube because those suckers are EXPENSIVE. :cool
 
S

speedmaster4

Guest
have seen ''intermittent failure'' in relays before...carry a spare...can't remember which (old age--the mind is second to go) but a bunch of the relays on these cars are all the same at connectors/ internals, just different mounting layouts...you can just plug em in and let em ''dangle'' for a short time, none ground thru the mounting.
 

Achilles

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Joined
Oct 31, 2004
Messages
447
Location
Back in Sunny California!
Corvette
1982 CE, 03 MY Z06
I agree, but it doesn't seem posible for the OD to continue working if the relay isn't there, which is the point of my question. I removed the relay. I thought the relay was the part that engages the OD. If it's not there, how can it engage?
 

G Winter

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Joined
Aug 21, 2004
Messages
2,177
Location
NW Iowa
Corvette
1990 red convert 6 sp
I have no idea how the electrical works on these but is it possible that the default is to engage and the relay locks it out ? Or that the the relay works on the normally closed side.


Glenn
:w
 

David-F

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Joined
Mar 28, 2007
Messages
53
Location
Woodstock,GA
You probably removed the wrong relay the O/D unit will not work with out the relay also in 86 the relay controled the dash O/D light so if ever the light comes on but doesn't go into O/D it's not the relay there are several things to look at if it is not turning on the O/D unit(no O/D light also) one would be the first gear switch if it's thinks it still in first it will not turn the O/D unit on. A falty relay is also a possible problem.

David Fulcher
 

Achilles

Well-known member
Joined
Oct 31, 2004
Messages
447
Location
Back in Sunny California!
Corvette
1982 CE, 03 MY Z06
You probably removed the wrong relay the O/D unit will not work with out the relay also in 86 the relay controled the dash O/D light so if ever the light comes on but doesn't go into O/D it's not the relay there are several things to look at if it is not turning on the O/D unit(no O/D light also) one would be the first gear switch if it's thinks it still in first it will not turn the O/D unit on. A falty relay is also a possible problem.

David Fulcher

Well, the fuel pump relay and OD relay are located together next to the brake booster on the firewall. The Fuel pump relay is behind the OD relay. These are the relays I'm refering to. When I switched relays between the two to see if one of them wasn't working, the car would not start with the defective relay connected to the fuel pump harness. So I reconnected the FP relay to the FP harness and it started right up. But I did not connect the OD relay back to its harness because I was going to get a new one to replace it. While driving the car, it popped into OD after warm up and worked perfect with no relay installed.

So, I don't know why that would be happening, but I haven't put the new relay in yet to see if it makes any difference.
 

David-F

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Joined
Mar 28, 2007
Messages
53
Location
Woodstock,GA
Achilles;
You stated that with the relay removed that when you drove the car the O/D engaged.....did the dash O/D light also come on? If so then you will need to check the connector for shorting wires because with the relay removed the O/D unit will be unable to recieve power to the O/D light or shift solenoid in the O/D unit. Also remember the car can run with out the fuel pump relay it could have extended crank but it should run there is an oil pressure switch which powers up the fuel pump when min oil pressure is reached.

David Fulcher
 

Achilles

Well-known member
Joined
Oct 31, 2004
Messages
447
Location
Back in Sunny California!
Corvette
1982 CE, 03 MY Z06
Yes the dash light and OD work as normal with out the relay installed.

New developement: Purchased a new relay and installed yesterday. Car will not start with new relay installed. Pulled new relay off, car started right up.

Checked fire to the plugs - none. Did all the standard ignition tracing:

Power to the coil - yes

Ign. module tested - good

pick-up coil tested - ok

Somewhere there is a short in the wire harness that run to the OD relay that have another function besides the trans OD unit. I wonder if anyone here has the wire diagram for this that could post? Or I could have a bad connector. The wiring done on these is really poor to begin with. Seems like I saw a post once where someone stated there was a company that made new connectors.
 

David-F

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Joined
Mar 28, 2007
Messages
53
Location
Woodstock,GA
Check the wiring at the connectors to make sure you have the correct relays, the fuel pump relay will have 2 red, 1 orange, 1 green/white, 1 black/white. The O/D relay will have 2 pink/black, 2 tan/black, 1 duble green. The two pink/black wires are powered by the gage fuse and the 1 tan/black terminal B goes to the ECM. I still suspect you have the relays swaped.

David Fulcher
 

Achilles

Well-known member
Joined
Oct 31, 2004
Messages
447
Location
Back in Sunny California!
Corvette
1982 CE, 03 MY Z06
Check the wiring at the connectors to make sure you have the correct relays, the fuel pump relay will have 2 red, 1 orange, 1 green/white, 1 black/white. The O/D relay will have 2 pink/black, 2 tan/black, 1 duble green. The two pink/black wires are powered by the gage fuse and the 1 tan/black terminal B goes to the ECM. I still suspect you have the relays swaped.

David Fulcher

Ok, you are correct. The harness I'm dealing with has 1 tan (could be orange), 1 green/white, 1 black/white & 2 red. Now the question is: why won't the car start with a new relay (or old one for that matter) plugged into the harness, but starts and runs without the FP relay? And do you know how to trace the problem?
 

David-F

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Joined
Mar 28, 2007
Messages
53
Location
Woodstock,GA
I suspect you may have a falty relay you know most of them are made in China what you need to check is get a test light hooked to groung and have someone turn the keey on(after the ECM has been powered down for over 20 seconds) and with the test lighton the fuel pump fuse and the other end on a good ground the light should light for 3 seconds and go out this is for fuel pump priming, If it doesn't try swaping with a known good relay and check again if it still doesn't then go to the connector and check for battery power to the orange wire and let me know what you find.

David Fulcher
 

Achilles

Well-known member
Joined
Oct 31, 2004
Messages
447
Location
Back in Sunny California!
Corvette
1982 CE, 03 MY Z06
Ok, decided to install the old relay back into the harness before trying the test light and the car started up immediately. Unlike w/o the relay the car would crank for a minute or two before starting. I'll take a test drive once the weather clears up to see if everything is back to normal.

There is no explanation for why it is working now. Before when I had the old relay installed and even the new relay installed, the car would just crank and not start at all. I assume there is a short somewhere.

Which fuse is the fuel pump fuse?
 

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