1989 digital dash
Thread Starter
Heel & Toe
Joined: Jul 2003
Posts: 17
Likes: 0
From: victorville CALIFORNIA
1989 digital dash
hello forum! this is the best place in the world for info, thank you to everyone who has ever posted anything on here, i read it all frequently. my problem is this. a few weeks ago the readout on my dash where it says current fuel mileage started fluctuating and is now stuck on 7.3, now a few weeks later my spedometer is not working, it will work a little bit then start fluctuating wildly up and down then just sit at zero. any suggestions would be very helpful and appreciated, thanks, gambleonus. 
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Signals are from two different sources. To check the mileage readout, verify the check engine light comes on when you turn on the key and that it will flash a code 12 when you ground the diagnostic connector. The mileage readout is on the same circuit as serial data and if the Check Engine light and diagnostics are ok, the ECM and it's circuitry are usually ok too, so the cluster generally needs to be swapped out. There is a possibility of a bad ground, but the '89 uses a different routing for one of the ground circuits and doesn't have the problems that the earlier models had. You can check it by jumpering Cluster Pin 1 to Pin 3. If nothing changes, it probably isn't the ground circuits.
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Your ECM calculates your fuel mileage from your Speedo... so if the speedo isnt working, your fuel mileage wont, I'd try and fix the speedo problem first. The speed signal generator is located on the transmissionIf you have a digital volt ohm meter, you can check whether its good or not yourself... but the procedure is pretty difficult. It doesn't sound like a ground problem because the rest of your gauges work right?
Heel & Toe
Joined: Aug 2004
Posts: 20
Likes: 0
Originally Posted by mikey whipreck
Your ECM calculates your fuel mileage from your Speedo... so if the speedo isnt working, your fuel mileage wont, I'd try and fix the speedo problem first. The speed signal generator is located on the transmissionIf you have a digital volt ohm meter, you can check whether its good or not yourself... but the procedure is pretty difficult. It doesn't sound like a ground problem because the rest of your gauges work right?
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
His Check Engine light might come on if the signal generator is bad... however if the connections to and from it are bad, he probably wouldn't get anything... If I remember right, the 84 has a different comp setup then the 89... Going over all the grounds would be the cheapest easiest place to start though, and if you do a search you'll find where they're all at (4 of them i believe)... It just doesnt sound like a ground problem to me...
Thread Starter
Heel & Toe
Joined: Jul 2003
Posts: 17
Likes: 0
From: victorville CALIFORNIA
Update on 1989 digital dash
Okay, got the trouble codes off, it first flashed the twelve, the gave me codes 24-vehicle speed sensor, and code 32-exhaust gas recirculation circuit. would the vehicle speed sensor have anything to do with the function of the spedometer and fuel mileage readout? they are still lit up but they stay at zero. also, i noticed that my odometer is not working, it is not electronic it is the old wheel/scrolling style. got under and checked cable thought maybe something was loose, cable seemed okay. i am going to bring it to our local chevy dealer who is rancho motors up here in Victorville Ca. i have been there a couple times and they do great work, i wouldnt trust anyone else but them. as soon as i hear what they say i'll re-post, until then any other suggestions are more then welcome, thanks a lot to everyoe who replied i really appreciate it, Gambleonus. 
Thread Starter
Heel & Toe
Joined: Jul 2003
Posts: 17
Likes: 0
From: victorville CALIFORNIA
1989 Digital Dash fixed!
Hello Forum! okay, brought my 1989 Corvette to the local dealer here in the high desert, they are Rancho Motor Company. Al Trudeau, and Debbie Demers were most instrumental with their customer service. i had pulled up trouble codes which said the vehicle speed sensor, and the egr valve were bad. Rancho replaced the egr valve and a new harness connector at the vehicle speed sensor. everything now works on my digital dash. before this i was getting readings of zero, meaning the display was working but no info was coming to it, now everything is great! thanks for all the responses i really appreciate it. 
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From: Canal Winchester OH
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Originally Posted by MidLCrs
The "Check Engine Light" was not comming on in my '84 however my gauges worked ok. Finally found a bad ground wire to the puter. Now my auto cruse works too.
