86' trans problem 4+3
Thread Starter
Intermediate
Joined: Apr 2010
Posts: 49
Likes: 0
From: Cambridge Maryland
86' trans problem 4+3
I finally took a long ride in the car. The overdrive will work sometimes and sometimes it won't. When the overdrive does work it will show the D symbol on the dash and go down the highway with low rpms. But then it will switch the overdrive off and the check engine light will come on and the "D" sysmbol will go off and the rpm's will go very high. I was wondering what this possibly could be. Thanks.
Cruising
Joined: Feb 2008
Posts: 14
Likes: 0
From: Averill Park NY
I just had the same problme with my 86 and it was not fixed untill a rebuild on the overdrive. Its ussually a sign of seal failer between overdrive and trans. The gear fluid in the overdrive can cas damage to the overdrive.
Advanced
Joined: Jun 2009
Posts: 74
Likes: 1
From: Fort Wayne IN
I'm in the same boat. We bought an '88 last summer and the seller told us that it was stuck in overdrive. Well, 70MPH and 3000RPM does not sound to me like the overdrive is 'on'. I had to repair the button switch on the shifter to get it to have D on or off on the dashboard. When the D is off, I can downshift and feel it. When the D is on, I can down shift and not notice a difference, I don't know why that is. I have also measure a voltage change at the wire that goes into the Overdrive unit when I press the button...so in my case it looks like something in the O/D itself. I have a plan to take it to a shop when I can get a morning off work.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Check fluid level in O/d 1st
If last service not known or done when due ( every 12K ) drop pan, replace filter and refill.
http://forums.corvetteforum.com/1571645223-post6.html
Heel & Toe
Joined: Dec 2009
Posts: 24
Likes: 0
From: Averill Park NY
86' trans problem 4+3
I finally took a long ride in the car. The overdrive will work sometimes and sometimes it won't. When the overdrive does work it will show the D symbol on the dash and go down the highway with low rpms. But then it will switch the overdrive off and the check engine light will come on and the "D" sysmbol will go off and the rpm's will go very high. I was wondering what this possibly could be. Thanks.
oil pressure; not in 1st gear; throttle position; Mass Air Flow. If one of these sensors is flaky or it's connection is intermittent the ECM will disengage overdrive. The "check engine light" may have set a code that could give you more information.
Pro
Joined: Oct 1999
Posts: 515
Likes: 0
From: Nashua NH
I'm in the same boat. We bought an '88 last summer and the seller told us that it was stuck in overdrive. Well, 70MPH and 3000RPM does not sound to me like the overdrive is 'on'. I had to repair the button switch on the shifter to get it to have D on or off on the dashboard. When the D is off, I can downshift and feel it. When the D is on, I can down shift and not notice a difference, I don't know why that is. I have also measure a voltage change at the wire that goes into the Overdrive unit when I press the button...so in my case it looks like something in the O/D itself. I have a plan to take it to a shop when I can get a morning off work.
Team Owner
Joined: Jan 2003
Posts: 20,305
Likes: 240
From: Summerland B.C. Canada
I finally took a long ride in the car. The overdrive will work sometimes and sometimes it won't. When the overdrive does work it will show the D symbol on the dash and go down the highway with low rpms. But then it will switch the overdrive off and the check engine light will come on and the "D" sysmbol will go off and the rpm's will go very high. I was wondering what this possibly could be. Thanks.
http://members.shaw.ca/corvette86/No...it%20Check.pdf
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Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Do it yourself with a paperclip 
There are no codes for O/d operation but it will show what code(s) the SES light was for
http://www.corvettebuyers.com/c4vettes/codes.htm
There are no codes for O/d operation but it will show what code(s) the SES light was for
http://www.corvettebuyers.com/c4vettes/codes.htm
Advanced
Joined: Jun 2009
Posts: 74
Likes: 1
From: Fort Wayne IN
Low fluid will do that amounst other things
Check fluid level in O/d 1st
If last service not known or done when due ( every 12K ) drop pan, replace filter and refill.
http://forums.corvetteforum.com/1571645223-post6.html
Check fluid level in O/d 1st
If last service not known or done when due ( every 12K ) drop pan, replace filter and refill.
http://forums.corvetteforum.com/1571645223-post6.html
Team Owner
Joined: Jan 2003
Posts: 20,305
Likes: 240
From: Summerland B.C. Canada
Thread Starter
Intermediate
Joined: Apr 2010
Posts: 49
Likes: 0
From: Cambridge Maryland
Well I hooked the car up to scanner and the engine light is not putting out codes. I even tried the paper clip and jump wire and still no codes. I took it for a drive today the engine light was on and the overdrive wouldn't work and didnt really have power and was missing a bit. On the ride home the engine light was still on but the overdrive worked perfect and the car had power and spun 1st 2nd and bit in third. I did put the scanner on and hit clear all codes but the scanner said nothing happend. I don't know whats going on with this car.
Water temp was about 190 oil temp about 220 and volts 14.0 and oil pressure about 55-62. I'm thinking of changing th ECM. where is the ECM located. I found something that looked like it behind the seat and it was unpluged for some reason along with a circuit breaker and when I plug the little breaker box up the ABS light came on.
Water temp was about 190 oil temp about 220 and volts 14.0 and oil pressure about 55-62. I'm thinking of changing th ECM. where is the ECM located. I found something that looked like it behind the seat and it was unpluged for some reason along with a circuit breaker and when I plug the little breaker box up the ABS light came on.
Last edited by kjr2492; Apr 19, 2010 at 09:26 PM.
Team Owner
Joined: Jan 2003
Posts: 20,305
Likes: 240
From: Summerland B.C. Canada
Thread Starter
Intermediate
Joined: Apr 2010
Posts: 49
Likes: 0
From: Cambridge Maryland
After looking at the attachment I do remeber locating a box with a computer chip inside and the box stating that it was a chip to add more power. Is it possible that the chip should go to stock and aybe burnt the ECM out? Also where is the computer chip located?
Last edited by kjr2492; Apr 20, 2010 at 09:26 PM.
Team Owner
Joined: Jan 2003
Posts: 20,305
Likes: 240
From: Summerland B.C. Canada
The chip is mounted into the ECM. The ECM is tucked under the passenger side dash. You have to remove the lower foot well panel and lay on you back and look up. It slides into a mount and is held in with two 10mm hex head screws.
I would try and diagnose the lack of code 12, when you have it hanging down.
I would try and diagnose the lack of code 12, when you have it hanging down.
Thread Starter
Intermediate
Joined: Apr 2010
Posts: 49
Likes: 0
From: Cambridge Maryland
The chip is mounted into the ECM. The ECM is tucked under the passenger side dash. You have to remove the lower foot well panel and lay on you back and look up. It slides into a mount and is held in with two 10mm hex head screws.
I would try and diagnose the lack of code 12, when you have it hanging down.
I would try and diagnose the lack of code 12, when you have it hanging down.
Thread Starter
Intermediate
Joined: Apr 2010
Posts: 49
Likes: 0
From: Cambridge Maryland
FINALLY!!!!!!!!! Well I pulled the ecm and my tester cam ein today and would not throw the code. The guy I bought the car from still had the stock computer chip. There was a hypertech installed. Well I put the stock one back in and engine light showed all 12. Cleared codes and started up and test drove. Car runs great and transmission is perfect. Thank you everyone for your help. Now I actuallt like my corvette that I bought for only $2,300 because he said its needs transmission becaude it wasnt shifting and running very bad.
Almost forgot to ask. Do you think the chip should not be used in there or do you think that the chip just went bad? Also are they even worth the money? I looked at it and come to find out its a stage 2 chip and not a 1.
Almost forgot to ask. Do you think the chip should not be used in there or do you think that the chip just went bad? Also are they even worth the money? I looked at it and come to find out its a stage 2 chip and not a 1.
Last edited by kjr2492; Apr 21, 2010 at 08:15 PM.