ECM Testing
Thread Starter
6th Gear
Joined: Jul 2018
Posts: 6
Likes: 1
ECM Testing
I have a LT1 motor and 6 speed from a 93 Corvette in my 56 Bel Air. I've just had an issue crop up where the car will run for 15-20 minutes and die.
When it dies, the fuel pump won't run. The check engine light doesn't come on when the key is first turned on. The engine will turn over but obviously won't start without the fuel pump running. I can force-run (with 12v) the fuel pump and the engine still doesn't run.
These things lead me to believe the ECM is crapping out after things get warmed up. The car has had a new fuel pump and fuel pump relay installed.
So, just to reiterate .. when the car has sat for a while (and cooled off), when I turn the key on, the check engine light comes on and I hear the fuel pump running for a few seconds as expected. Turn the key to start and it fires right up.
After the car runs for a while (15-20 minutes) the engine dies and the fuel pump does NOT turn on with the key in the "ON" position, and the check engine light does NOT come on when you first turn the key on.
Any help confirming an issue with the ECM ? What's a good way to test / troubleshoot that thing ?
Thank you !
When it dies, the fuel pump won't run. The check engine light doesn't come on when the key is first turned on. The engine will turn over but obviously won't start without the fuel pump running. I can force-run (with 12v) the fuel pump and the engine still doesn't run.
These things lead me to believe the ECM is crapping out after things get warmed up. The car has had a new fuel pump and fuel pump relay installed.
So, just to reiterate .. when the car has sat for a while (and cooled off), when I turn the key on, the check engine light comes on and I hear the fuel pump running for a few seconds as expected. Turn the key to start and it fires right up.
After the car runs for a while (15-20 minutes) the engine dies and the fuel pump does NOT turn on with the key in the "ON" position, and the check engine light does NOT come on when you first turn the key on.
Any help confirming an issue with the ECM ? What's a good way to test / troubleshoot that thing ?
Thank you !
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
The check engine light part sounds like ecm. Verify power and grounds ideally when it's not working. Also check if there happens to be any codes. ECM is 92-93 LT1 only can be hard to find. Remans normally send one to get one. The a companies who will repair yours.
Thread Starter
6th Gear
Joined: Jul 2018
Posts: 6
Likes: 1
The ECM has a part number of 7-9278 on it and has the 4 connections on the top (grey / red / green / brown)
Last edited by RacerX10; Jul 11, 2018 at 02:19 PM.
Thread Starter
6th Gear
Joined: Jul 2018
Posts: 6
Likes: 1
Hadn't thought of anything that simple 
Does the IGN switch power the ECM ?
Even when it's shut itself down (after warming up) and I don't get the check engine light, I *do* still get OIL light on dash since the engine is "on" but not running. Would that eliminate the IGN switch as a culprit ?
Thanks !
Does the IGN switch power the ECM ?Even when it's shut itself down (after warming up) and I don't get the check engine light, I *do* still get OIL light on dash since the engine is "on" but not running. Would that eliminate the IGN switch as a culprit ?
Thanks !
Last edited by RacerX10; Jul 11, 2018 at 03:14 PM.
Thread Starter
6th Gear
Joined: Jul 2018
Posts: 6
Likes: 1
I appears that the wire harness for the ECM draws power from the starter lug (where the main line from the battery positive terminal comes up) so I guess that's where I start looking. I guess the ECM stays powered up all the time.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
ECM has both constant 12v and ignition 12v feeds. Checking during failure should confirm ECM or car is at fault. You could try to Google ECM wiring diagram or pin out. I don't have a way to share it.
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Thread Starter
6th Gear
Joined: Jul 2018
Posts: 6
Likes: 1
Thought I would update this thread with the solution. Pulled the ECM out, took it out of it's case and did a little poking around while it was still hooked up. Found out that I could reproduce the problem with slight tapping or very slight PCB flexing of the ECM PCB. Re soldered all the connections on the IC's attached to the heat sink (those are usually the most common points to find cold solder joints) and the car seems to be running fine now. Ran it about 30 minutes in the shop and never missed a beat.
Thanks again for all the advice given.
Thanks again for all the advice given.
