88 coupe - problem with MPG display
Thread Starter
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
88 coupe - problem with MPG display
Recently, my average mpg display has been showing 12.8 mpg. I didn't think anything of this as I have only been driving in town the last couple weeks. Today I got out on the highway for a bit and the display didn't change. I tried to reset it, but it still shows 12.8mpg. The instant mpg does reset and display correctly. I even disconnected the battery to reset the computer and it still shows 12.8mpg.
Where does the signal for this display come from, the ecm? I took off the DIC with the switches and the wiring looks good back there. I don't think it's a problem with the LCD because it will show the instant mpg. I'm not sure where to start troubleshooting this problem. Any suggestions would be much obliged.
Where does the signal for this display come from, the ecm? I took off the DIC with the switches and the wiring looks good back there. I don't think it's a problem with the LCD because it will show the instant mpg. I'm not sure where to start troubleshooting this problem. Any suggestions would be much obliged.
Racer
Joined: Mar 2001
Posts: 312
Likes: 0
From: Mesa Az
Function select switch
Looking at the electrical schematic in the supplement manual there is a BRN wire going from the DIC to the instrument cluster. Per the manual 1. "Disconnect the Telltale Assembly connector from the Instrument Cluster. Locate the wire terminal of the function that does not operate properly and measure the resistance between the terminal and terminal B1 (BLK) with the Switch being tested in the OFF position. [Your lead in question is A1.]
. If the resistance is infinite ohms, go to step 2.
. If the resistance is zero ohms, replace the faulty Switch or the entire Telltale Assembly
2. With the Ohmmeter still connected between the suspect Switch terminal and Terminal B1 (BLK), hold the suspect Switch in the position to select the desired function.
. If the resistance is infinite ohms, replace the faulty Switch or entire Telltale Assembly.
. If the resistance is zero ohms, replace the Instrument Cluster.
I'm guessing it's the switch since everything else works.
. If the resistance is infinite ohms, go to step 2.
. If the resistance is zero ohms, replace the faulty Switch or the entire Telltale Assembly
2. With the Ohmmeter still connected between the suspect Switch terminal and Terminal B1 (BLK), hold the suspect Switch in the position to select the desired function.
. If the resistance is infinite ohms, replace the faulty Switch or entire Telltale Assembly.
. If the resistance is zero ohms, replace the Instrument Cluster.
I'm guessing it's the switch since everything else works.
Burning Brakes
Joined: Apr 2004
Posts: 792
Likes: 1
From: Stanfield NC
I am no expert, but couldn't it also be related to a vacume problem? I recently installed a mini ram on my 88 and in the process intentially eliminated the cruise control which also disable the MPG read out on the dash. This is my track car so no big deal. There is a very small vacume line near the fire wall in the area of the distributer that goes to both the cruise and the dash. eep us posted on your progress.
Thread Starter
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
Thanks for the suggestions guys. I will poke around at the electrical tomorrow. I know the vacuum connection your referring to wndopdlr, but my cruise is working normally. I used it today when I noticed the display problem.
This evening I noticed that the range function is no longer working either. Guess I have to break out the service manual and start tracing wires.
Thanks again guys.
This evening I noticed that the range function is no longer working either. Guess I have to break out the service manual and start tracing wires.
Thanks again guys.
Racer
Joined: Mar 2001
Posts: 312
Likes: 0
From: Mesa Az
dash cluster
I just got mine back today, the center cluster was cracked. They also changed the power supply and replaced all the lamps with Zeon. I'll know tomorrow if it works. Maybe your cluster is going out. Hope not.
Thread Starter
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
Originally Posted by 88JDO
I just got mine back today, the center cluster was cracked. They also changed the power supply and replaced all the lamps with Zeon. I'll know tomorrow if it works. Maybe your cluster is going out. Hope not.
Pro
Joined: Feb 2005
Posts: 658
Likes: 1
From: Centerville OH
Originally Posted by JCAIRE2
This evening I noticed that the range function is no longer working either. Guess I have to break out the service manual and start tracing wires.
Thanks again guys.
Thanks again guys.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Drifting
Joined: May 2001
Posts: 1,630
Likes: 0
From: Brandywine, Chester and Ridley Valleys Pennsylvania
My 88 did this for the longest time when I was running TPI. I also noticed that it didn't run quite as crisply when it "crapped out" as when the mpg/range was working correctly. Open loop was th same, but when soft-pedalling around, engine response was a little more "ham-fisted" Sometimes it would get "stuck" on a number, like 33 mpg, sometimes it would be 99 or 0 or 12.8.
Also, when this would happen, a scan tool would not connect to the computer.
Bought a $99 refurbished computer from Eckler's and problem solved. I don't know if it was the connectors on the computer or what, but after that I never had any more problems and the scan tool worked fine 100% of the time.
Also, when this would happen, a scan tool would not connect to the computer.
Bought a $99 refurbished computer from Eckler's and problem solved. I don't know if it was the connectors on the computer or what, but after that I never had any more problems and the scan tool worked fine 100% of the time.
Thread Starter
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
Originally Posted by TrueBlue ChevyDude
My 88 did this for the longest time when I was running TPI. I also noticed that it didn't run quite as crisply when it "crapped out" as when the mpg/range was working correctly. Open loop was th same, but when soft-pedalling around, engine response was a little more "ham-fisted" Sometimes it would get "stuck" on a number, like 33 mpg, sometimes it would be 99 or 0 or 12.8.
Also, when this would happen, a scan tool would not connect to the computer.
Bought a $99 refurbished computer from Eckler's and problem solved. I don't know if it was the connectors on the computer or what, but after that I never had any more problems and the scan tool worked fine 100% of the time.
Also, when this would happen, a scan tool would not connect to the computer.
Bought a $99 refurbished computer from Eckler's and problem solved. I don't know if it was the connectors on the computer or what, but after that I never had any more problems and the scan tool worked fine 100% of the time.
Hmm this is interesting. I had the car hooked up to the laptop yesterday to record some WOT runs with datamaster. It connected fine, so it's not the ECM. I guess I will check the bulkhead connector and the ECM wiring connection.
Thanks guys.
