ECM being flakey on 93 LT1
Thread Starter
Intermediate
Joined: Oct 2003
Posts: 36
Likes: 0
From: Central NJ
ECM being flakey on 93 LT1
The ECM on my 93 LT1 6-speed is doing some weird things. Sometimes the car will run fine, but other times it runs like its timing is off and throws an ASR and SES light, and I loose all digital gauges including speed. No codes are available when this happens, not using the paperclip method or a scanner. The scanner says it's unable to communicate with the car. If I pop the hood and tap the ECM unit everything springs back to life and the car runs great and there are no codes to be read.
I'm pretty sure this isn't related to a loose wire on the harness going to the ECM because I've jiggled them while the car was running and nothing happens. The only time I can produce/solve the problem is by tapping on the metal enclosure. I checked that the PROM was seated tightly. Am I looking at an ECM that's on its way out or needs to be replaced? Or is there a simple solution that I haven't been able to find yet?
I'm pretty sure this isn't related to a loose wire on the harness going to the ECM because I've jiggled them while the car was running and nothing happens. The only time I can produce/solve the problem is by tapping on the metal enclosure. I checked that the PROM was seated tightly. Am I looking at an ECM that's on its way out or needs to be replaced? Or is there a simple solution that I haven't been able to find yet?
Advanced
Joined: Sep 2005
Posts: 97
Likes: 0
From: Stockholm / Sweden
Team Owner
Joined: Sep 2003
Posts: 25,295
Likes: 4
From: I'm the walkin dude I can see all of the world...
St. Jude Donor '03
I have the same issues and it turned out to be the ECM/CCM grounds located directly above the oil filter. Replaced the ECM and it was no help. Cleaning and adjusting the grounds did the job. 
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Some of the things you described sounds like CCM functions. I would be open minded and possibly looking in some different areas. All are good suggestions so far but it would take a lot of heat to get the ECM hot enough because it is a large mass of metal and you don’t really know what’s going on inside. It gets pretty hot during normal driving.
Although those year ECMs have a reputation, I would not change it so fast but look for an external problem (connection or such) before you go an buy one. Unless you just have a spare one to try.
Although those year ECMs have a reputation, I would not change it so fast but look for an external problem (connection or such) before you go an buy one. Unless you just have a spare one to try.
Thread Starter
Intermediate
Joined: Oct 2003
Posts: 36
Likes: 0
From: Central NJ
Thanks for the responses guys. I'm leaning towards it actually being the ECM and not the connections on the back or a loose wire outside the unit. I can hold the ECM still, move the wires, and not replicate the problem but if I remove the cover for the PROM and tap the chip or board even the slightest bit the issues come back. So I guess it sounds like I need a new ECM.
Anyone know a good place to get one? I've checked the regular places out and everyone seems to be out of stock on them.
Anyone know a good place to get one? I've checked the regular places out and everyone seems to be out of stock on them.
Heel & Toe
Joined: May 2006
Posts: 20
Likes: 0
Ecm
Had the ECM changed a 2nd time at the dealer and now the car runs fine (only 20 miles so far), '92 was at the dealer almost a month waiting for the ac-delco part. Could get a aftermarket overnight but the dealer said they would not warranty anyhting that would "go" associated with "that" ECM only theirs.
Do you believe it- 1 "month" to get an american car part.
Do you believe it- 1 "month" to get an american car part.
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
Thread Starter
Intermediate
Joined: Oct 2003
Posts: 36
Likes: 0
From: Central NJ
Originally Posted by tennis1
Could get a aftermarket overnight but the dealer said they would not warranty anyhting that would "go" associated with "that" ECM only theirs.
Thread Starter
Intermediate
Joined: Oct 2003
Posts: 36
Likes: 0
From: Central NJ
Ok...so I sourced a reman ECM local to me, installed it, and now the car won't even start. I'm getting ATS, SES, and SYS like I was before, but now it cranks and doesn't start. Getting a code 12 (using the paperclip method) but the code reader can't communicate with the car. Is there something that I need to do to reset the communications between the CCM and ECM or something? I'm 98% sure the old ECM was bad based on what I had to do to get the car to run properly, but now I'm questioning it.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Check the basics first. Fuel pressure and spark. A SYS is generated by the CCM. A code 12 says that there are no codes stored and the CCM is communicating and happy. The scanner interfaces with the CCM and if it can't, the CCM might not be working OK. If it cranks, VATS is OK but FEDS might not be.
I would not rely on fixing the car using codes, it may not be reliable and not yield real information. I think basic troubleshooting is going to be necessary in this case.
I cannot disagree with your physical initial findings, but I think you need to broaden the search and see what basic functions might be lacking.
I would not rely on fixing the car using codes, it may not be reliable and not yield real information. I think basic troubleshooting is going to be necessary in this case.
I cannot disagree with your physical initial findings, but I think you need to broaden the search and see what basic functions might be lacking.
Instructor
Joined: Jul 2004
Posts: 210
Likes: 0
From: Lakewood CO
Originally Posted by VR'92
Could be a bad prom.
Has anyone had their prom go bad and cause similar problems? I saw your post about the ground next to the oil filter solving your problems. I will be checking mine this weekend as I have had similar problems to yours since I got the car last September.
Dave
Le Mans Master
Joined: Dec 2004
Posts: 7,475
Likes: 2
From: Austin TX
St. Jude Donor '07
Originally Posted by VR'92
I have the same issues and it turned out to be the ECM/CCM grounds located directly above the oil filter. Replaced the ECM and it was no help. Cleaning and adjusting the grounds did the job.
This might explain my problem.. Not sure if it's related, but, a couple of weeks ago my "low oil" light come on (even though the oil level was fine), I turned the car off and then back on, the low oil light never did return, but now i'm having the sys/security/asr problem. Not sure if the oil indicators sensors are at the same area as the ecm/ccm ground. I'll have to crawl underneath the car and look.
