4+3 overdrive woes
Thread Starter
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
4+3 overdrive woes
Hey guys, my car (86, manual) has been laid up since early april, overdrive worked fine, I had a bad egr valve and removed the plenum, distributor cap, and associated hoses around the engine. made the egr change, engine starts and runs fine but no OD. no light on dash, no sound. Checked fuse, checked switch on shifter for continuity, OK.
dash shows MPH & tach, water temp OK.
What is the "flow chart" for debugging this thing?
Thanks,
Tom
dash shows MPH & tach, water temp OK.
What is the "flow chart" for debugging this thing?
Thanks,
Tom
Safety Car
Joined: Jul 2006
Posts: 3,696
Likes: 1
From: MA
Check your relay or relay plug.
Its location is next to fuel pump relay right behind plenum on firewall.
Both fuel pump relay and OD relay share the same relay part#
Maybe Central Coaster will chime in..He knows these 4+3 very well and has help me in the past when I had my 86
Good luck
Its location is next to fuel pump relay right behind plenum on firewall.
Both fuel pump relay and OD relay share the same relay part#
Maybe Central Coaster will chime in..He knows these 4+3 very well and has help me in the past when I had my 86
Good luck
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Get a paperclip and jumper the diagnostic connector pins A&B (top two on right)
With key on, the overdrive light should come on. Also make sure the gages fuse is okay.
And check the relay connections, or just swap plugs with the fuel pump relay next to it. It's left of the brake booster. The engine heat causes the wire insulation to shrink and short out.
Post up here on what happens.
With key on, the overdrive light should come on. Also make sure the gages fuse is okay.
And check the relay connections, or just swap plugs with the fuel pump relay next to it. It's left of the brake booster. The engine heat causes the wire insulation to shrink and short out.
Post up here on what happens.
7th Gear
Joined: Dec 2006
Posts: 7
Likes: 0
If it's like my 84 you might want to check the vacuum lines.
A vacuum diagram sticker should be under the hood by the radiator.
also if you were under the car for some other reason you could have disconnected the wire plug that connects to the OD unit.
I had my oil changed and the guy disconnected my plug.
What ever helps right ?
Good luck
A vacuum diagram sticker should be under the hood by the radiator.
also if you were under the car for some other reason you could have disconnected the wire plug that connects to the OD unit.
I had my oil changed and the guy disconnected my plug.
What ever helps right ?
Good luck
Team Owner
Joined: Jan 2003
Posts: 20,322
Likes: 248
From: Summerland B.C. Canada
Thread Starter
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
Get a paperclip and jumper the diagnostic connector pins A&B (top two on right)
With key on, the overdrive light should come on. Also make sure the gages fuse is okay.
And check the relay connections, or just swap plugs with the fuel pump relay next to it. It's left of the brake booster. The engine heat causes the wire insulation to shrink and short out.
Post up here on what happens.
With key on, the overdrive light should come on. Also make sure the gages fuse is okay.
And check the relay connections, or just swap plugs with the fuel pump relay next to it. It's left of the brake booster. The engine heat causes the wire insulation to shrink and short out.
Post up here on what happens.
No OD lite, fuses OK - relay harness looks like hell, but no shorts,
will swap it with the fuel pump relay
Tom
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Thread Starter
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
Agent86, thanks for the flow charts, I see they manual says to have engine up to operating temp., shunt A&B and check for the light.
CentralCoaster,
My engine is cold, will that make a difference?
Tom
CentralCoaster,
My engine is cold, will that make a difference?
Tom
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
No, temperature doesn't matter in diagnostic mode.
Shorting A+B makes the computer send ground signals to pretty much everything, including the overdrive relay. (Key on, engine off). So no matter what temp the car is, what gear its in, if your shifter switch is on, doesn't matter, it will still try to turn on the overdrive.
If the light isn't coming on, most likely the relay either isn't getting this ground signal, or is not responding to it.
Bad connection to relay, or bad relay.
Shorting A+B makes the computer send ground signals to pretty much everything, including the overdrive relay. (Key on, engine off). So no matter what temp the car is, what gear its in, if your shifter switch is on, doesn't matter, it will still try to turn on the overdrive.
If the light isn't coming on, most likely the relay either isn't getting this ground signal, or is not responding to it.
Bad connection to relay, or bad relay.
Thread Starter
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
CentralCoaster, it was actually your 1st item, and the thing that I checked 1st visually, the gages fuse, after i metered the relay plug and found no voltage on C or E i went back and pulled the fuse and put the ohm meter on it and sure enough it was bad. Popped in a new 10 amp and shorted A&B, the OD light came on.
Thank you & Agent86
- Tom
Thank you & Agent86
- Tom
Safety Car
Joined: Jul 2006
Posts: 3,696
Likes: 1
From: MA
I remember you telling me about that
I also remember seeing pictures
CC you dah man
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Most of the threads I've seen about the overdrive are simple electrical issues, (Well, simple if you know the wiring setup at least)
In fact I can't recall a single one where it was narrowed down to mechanical failure of the overdrive. Well, in repzard's case I think it did fail, but it was full of gear oil, probably from a leaking front seal. Fill any automatic with gear oil and it won't last long.
In fact I can't recall a single one where it was narrowed down to mechanical failure of the overdrive. Well, in repzard's case I think it did fail, but it was full of gear oil, probably from a leaking front seal. Fill any automatic with gear oil and it won't last long.
Last edited by CentralCoaster; May 16, 2007 at 07:30 PM.