C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

4+3 OD help

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Old Mar 18, 2009 | 10:53 PM
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Default 4+3 OD help

so I just purchased this corvette in febuarary and have been restoring her she was running really poorly and have fixed several issues including the vacume lines and the biggest bugger a egr exhaust tube over the passenger side valve cover but my latest issue is the OD is turning on in first gear on its own with as well as in 2nd and 3rd the majority of my problems is that if the OD comes on in first it chokes the engine and makes it stall while im driving >.<;; now the people before me installed their own switch for the OD basically they dissconnected the one from the shifter and ran their own switch through the cigarete lighter I have already tested the switch and its good so im confused and not sure what to do from here any help would be appreciated!!! thanks!

sorry about that its a 1986

Ian~

Last edited by suigen; Mar 18, 2009 at 11:19 PM.
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Old Mar 18, 2009 | 11:10 PM
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What year ??
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Old Mar 18, 2009 | 11:53 PM
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Here is info on the 86 OD.
http://members.shaw.ca/agent86/Overdrive-manual.pdf

http://members.shaw.ca/agent86/OverD...Electrical.pdf

If all is working normally, the OD will kick on as soon as the ECM sees what it wants to see, such as coolant temp,RPM, TPS, etc. 1st gear isn't supposed to be over-driven, but it happens to mine occasionally, too.
Before I burned my own ECM PROM, I used to watch the coolant temp and get ready to hit the OD button. Unfortunately, on our 86's you can't do nothing with the OD switch until it reaches the target coolant temp.
Read the info I gave you in the links. It will help you understand the OD system and how to diagnose it's problems.
Good Luck.
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Old Mar 19, 2009 | 12:18 AM
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Originally Posted by AGENT 86
Here is info on the 86 OD.
http://members.shaw.ca/agent86/Overdrive-manual.pdf

http://members.shaw.ca/agent86/OverD...Electrical.pdf

If all is working normally, the OD will kick on as soon as the ECM sees what it wants to see, such as coolant temp,RPM, TPS, etc. 1st gear isn't supposed to be over-driven, but it happens to mine occasionally, too.
Before I burned my own ECM PROM, I used to watch the coolant temp and get ready to hit the OD button. Unfortunately, on our 86's you can't do nothing with the OD switch until it reaches the target coolant temp.
Read the info I gave you in the links. It will help you understand the OD system and how to diagnose it's problems.
Good Luck.
well the issue is its happening very frequently and sometimes when it happens i can push the button to turn it off and it turns right back on as soon as im done pressing the button >.< but it causes the engine to stall whenever it does this in the first gear but it isint always doing this part of the time it works normally and i get to 4th and manual engage the OD and works perfectly which is why im so confused?? also its doing it at normal temps like 220 but it also did it tonight at a 170 so that confused me as well... but thank you for the schematics in those Ive been looking everywhere for some!
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Old Mar 19, 2009 | 02:00 AM
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Check the O/d relay for bad insulation common on early connectors.
Could have intermittent short causing O/d to engage independent of ECM control
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Old Mar 19, 2009 | 08:51 AM
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Originally Posted by rodj
Check the O/d relay for bad insulation common on early connectors.
Could have intermittent short causing O/d to engage independent of ECM control
okay this might sound like a stupid question... but where exactly is the overdrive relay ^^: i only have a chilton manual and not finding much info online...
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Old Mar 19, 2009 | 05:55 PM
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Originally Posted by suigen
okay this might sound like a stupid question... but where exactly is the overdrive relay ^^: i only have a chilton manual and not finding much info online...
On the firewall; should be two one for fuel pump ,one for O/d
Check pump relay connections while you are there
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Old Mar 19, 2009 | 07:24 PM
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Originally Posted by suigen
okay this might sound like a stupid question... but where exactly is the overdrive relay ^^: i only have a chilton manual and not finding much info online...
http://members.shaw.ca/corvette86/Co...0View%2086.pdf
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