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Replaced ECM but still have problems Please Help!


Active member
Aug 30, 2007
1981 White Coupe
I replaced the ECM and PROM today but the check engine light is still on. I did make some progress today because the car will now start and run when the wiring from the distributor to the ECM is connected. Which it would not do before I replaced the ECM. I tried to jump together the D&E terminals at the diagnostic port but could not get the check engine light to flash any codes the check engine light just stay on. The car still wants to hesitate and bog down when driving. It appears to run great in the garage but not when you get her out on the road it runs like crap. Does anyone have any ideas? I'm at a loss!


P Martin
Wiring or connections may be bad. Usually the middle of a wire is never the problem, so I would check and clean the connections at the computer, carb (MC and TPS), distributor (4 pin), O2 sensor, vacuum sensor (on driver's side firewall) and temp sensor (front passenger side if intake manifold). I highly recommend this stuff:

DeoxIT Standard Deoxidizer Aerosol Spray 5oz - eBay (item 360113144801 end time Jan-01-09 14:59:46 PST)

Unplug, brush off, apply a little of this and re-plug. With our 27 year old electronics, this is fifteen minutes well spent even if it does not fix this problem (which it may).

Bottom line is, the system is not working yet. Once we figure out why, it will be an easy fix so don't give up.

God bless, Sensei
Have you checked the O2 sensor? Sometimes those get fouled or the connections get crispy. It's on the drivers side exhaust just below the manifold.
Thanks for the tips guys. I'll work on cleaning all of the electrical connections and take a look at the O2 sensor tomorrow. This car has worked me over today. What's bothering me is I can't get any codes to flash. I feel like I'm shooting in the dark here.


P. Martin
Years ago I bought an 82 CE that had an engine stumble and the check engine light coming on. I removed the ECM (the car was only a few years old at the time) and found someone had already replaced the ECM. This was probably the reason why they sold the car. I cleaned the ECM edge connector contacts very good. I then removed each pin from the connector and cleaned it. I never again had any problem. The ECM was probably not bad to begin with. That edge connector setup is a pretty lame way of hooking up a device, expecially in a car that sees climate changes. What do you expect for Chevy's first attempt at an ECM?

Good luck!
All great suggestions. One has to to start somewhere while troubleshooting, and keeping it simple (the old K.I.S.S. adage) does solve the majority of the problems.

I noticed that you mentioned the difference in performance of the engine between idling and driving, so this could be a long shot, but it is worth checking. If you have a stock speedometer, check to make sure that the speed sensor has not fallen out from behind the speedo gage.

If it has a 140 MPH speedo, then perhaps it was not correctly upgraded and it could be that it does not have the speed sensor feature (but the sensor should be back there behind the speedo just the same)? ;shrug

Long shot, I know, but the speed sensor plays many roles in the L81.

Also, does your car has the EGR valve solenoid hooked-up and operational? If it is not connected or working, then it could be that it is not completing the tq converter lock-up signal for the computer. But this would be for the "Engine-Check" light being on.


Sooner or later, we can help you figure out what the cause of the problem is, so do not despair.:thumb
Ok, I worked most of the day cleaning electrical connections and replacing the O2 sensor with no luck. I guess its time for the carb to be rebuilt. Sensei do you know anybody in Jacksonville that could rebuild a E4ME? I can swing by autozone again :) (I'm starting to become a regular) and pick up an EGR valve and try that but my gut is telling me its the carb.


P. Martin
What part of town are you in and can you limp the car to Orange Park? I'd like to hook my diagnostic computer to it, although I don't count on it helping. If it is the carb, I'd be willing to rebuild it for you for the cost of the materials, the only problem is when I'll have the time.

God bless, Sensei
I pulled the ECM out again this morning and reseated the PROM. Problem Solved!!!:) She's running like a champ now!!! Thanks for all your help guys. I'm sure glad we have this forum to help a newbies like me. Thanks agian.
congrats!! Just like old pinball machines, check the connections. Most problems seem to be connections.
You can say that again!

Most battery/starter/alternator problems are with connections, also.

Woohoo! :thumb

The majority of the troubleshooting has to be done by the owner/member, but with the positive hints and coaching from our membership, one can begin to make some real progress with our rides.


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