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4+3 transmission odd behavior

MatthewMI

Member
Joined
Nov 16, 2016
Messages
19
Location
Lansing, MI
Corvette
1988 35th Anniversary
Hi guys,
My 88 4+3 is finally out and moving under its own power after buying it in pieces. As my last c4 was an automatic, the 4+3 is a bit of mystery to me. My issues are that I do not get a shift light, or the over drive light. The car does go into overdrive in 2, 3 and 4th gears but feels like it goes in earlier than I would expect. Let off the gas causes the overdrive to kick back out. Stepping in the gas again kicks it back on. The overdrive button will kick the overdrive off if you press and hold it. If you just press it, it does nothing.

I have checked all the fuses, the bulbs for the indicators light when you turn the key as all the lights come on. The only other thing that doesn't work right now is the cruise control. Not sure if it may just be a coincidence or related.

Any thoughts? I have never been able to find this issue in searching the web so far.
Thanks
 
The overdrive uses the same output and driver in the ECM as the Converter Clutch in an automatic. It seems like you have an automatic transmission PROM. The TCC drops out with zero-throttle, and re-engages after getting back on the gas. Like your overdrive is doing. I don't have an answer for the button-holding behavior.

Seems like a previous owner did some parts swapping without paying attention to details of the configuration.
 
The overdrive uses the same output and driver in the ECM as the Converter Clutch in an automatic. It seems like you have an automatic transmission PROM. The TCC drops out with zero-throttle, and re-engages after getting back on the gas. Like your overdrive is doing. I don't have an answer for the button-holding behavior.

Seems like a previous owner did some parts swapping without paying attention to details of the configuration.

You are right on the money! The previous owner had the prom stolen while it sat for years waiting to be repaired. Must have replaced with an automatic prom!
Thanks for the confirmation. It seems to work well otherwise.
 

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