Ignition Control Module???

[rob67gmc]

What can cause the ICM to go bad? Mine quit a few months ago. Replaced it and everything fine until last week. Quit again and I had just bought new plugs, wires, dist.cap and rotor but had not put them on yet. Changed plugs, wires, etc. then got a new ICM and car started fine. Ran it around a little that evening and next morning but that evening it would not start again. It is an '89 Camaro with an '89 Trans Am TPI 350. VATS has been bypassed.

Thanks,
Rob

[silicon212]

Originally Posted by rob67gmc

What can cause the ICM to go bad? Mine quit a few months ago. Replaced it and everything fine until last week. Quit again and I had just bought new plugs, wires, dist.cap and rotor but had not put them on yet. Changed plugs, wires, etc. then got a new ICM and car started fine. Ran it around a little that evening and next morning but that evening it would not start again. It is an '89 Camaro with an '89 Trans Am TPI 350. VATS has been bypassed.

Thanks,
Rob

On the two wire connection between the coil and the distributor, there is a pink wire and a white wire. This connects to the coil. Off of the coil, is another pink wire and possibly a white wire. The pink wire supplies power to the coil and dist, the white wire is a tach lead. On most cars, the white wire is not connected and is left to hang off in space (though usually covered with tape). Make sure this is not shorting out against the block, intake or any other engine component.

[rob67gmc]

Thanks silicon212, I checked those wires and they all seem to be ok. Put another ICM in and also a spare coil I had. Still nothing when I turn the key. I can get it to turn over by jumping the solenoid but it still won't fire. Open to any other ideas. I am totally lost on this one.

[silicon212]

The only other thing I can think of is the coil itself - have you tried a different one?

[Blue Bowtie]

Measure the resistance of the pickup coil both through the coil and to ground. The pickup coil should measure between 500 and 1,500 ohms (out of circuit) through the coil and should have infinite resistance to ground.

It's also pretty common for the HEI module connectors and pickup coil connectors to suffer heat damage and fail, so inspect those closely.

Take a close look at the reluctor for the pickup coil. Cracks can cause poor signal generation and insufficient energy to trigger the HEI module. Heavy rust on the reluctor can interfere with good signal generation.

[j cAT]

Originally Posted by rob67gmc

What can cause the ICM to go bad? Mine quit a few months ago. Replaced it and everything fine until last week. Quit again and I had just bought new plugs, wires, dist.cap and rotor but had not put them on yet. Changed plugs, wires, etc. then got a new ICM and car started fine. Ran it around a little that evening and next morning but that evening it would not start again. It is an '89 Camaro with an '89 Trans Am TPI 350. VATS has been bypassed.

Thanks,
Rob

the ICM is heat sensitive. if you installed one and did not clean and add the thermal compound to the module heat sink this is why they will rapidly fail.

any arcing will damage the ICM. bad wires / poor electrical connections. possibly a bad ground .

cold no start could be other things sure its bad/no spark ?

autozone has in most stores a tester made by wells. they can test it for you.

who made the ICM you have installed. new means its never been used ?

[rob67gmc]

New plugs, wires, dist.cap and rotor, coil. ICM's from NAPA and Autozone, new, not re-manufacturer. Used the thermal compound under ICM. Getting nothing when turning key. Changed the ignition switch mounted on the column under the dash yesterday. Still nothing. Going to try a different distributor this evening if I have one.

[silicon212]

Originally Posted by rob67gmc

New plugs, wires, dist.cap and rotor, coil. ICM's from NAPA and Autozone, new, not re-manufacturer. Used the thermal compound under ICM. Getting nothing when turning key. Changed the ignition switch mounted on the column under the dash yesterday. Still nothing. Going to try a different distributor this evening if I have one.

Just a hunch - try disconnecting the 4-wire ECM harness from the ICM, as if you were checking/adjusting the timing, and see if the car starts ...

One other thing - if the car isn't turning over when you turn the key, check the connection where the wiring harness passes through the firewall. Usually a bolt in the center of the block that holds it on - loosen this screw, pull the block off and reseat it.

[rob67gmc]

I disconnected the 4-wire ECM harness, still nothing. Then the wiring harness where it passes through the firewall, nothing. I changed the two fusible links near the starter, nothing. Then as I was moving a wiring harness around a friend was turning the key and got power for just a second. I pulled a long section of the plastic cover off the wires and found another fusible link. When I wiggled it we momentarily got power again. Changed it and car started right up. Stopped and started it several times, let it run for about an hour, then drove it around the neighborhood a few times. Running great.

Thanks for all the help. I'll let you know if it happens again.

Rob

[j cAT]

Originally Posted by silicon212

Just a hunch - try disconnecting the 4-wire ECM harness from the ICM, as if you were checking/adjusting the timing, and see if the car starts ...

One other thing - if the car isn't turning over when you turn the key, check the connection where the wiring harness passes through the firewall. Usually a bolt in the center of the block that holds it on - loosen this screw, pull the block off and reseat it.

great work tracking down the bad fuseable link. these when they intermittently fail are tough to find ,especially if hidden in the loom covering.

so was this the wire harness link on top/back of the engine ?

why do you think it went bad ?

[rob67gmc]

I don't really think I tracked down this link. More like I stumbled on it with some blind luck.

This harness came from the starter back toward the front of the engine, then split. One section went across the front of the engine towards drivers side and the other went towards the back on the passenger side, just below the fuel rail. The link was also on the same wire as one of the other links. Don't know why two links were on one wire. Still have no idea why it went bad.

[j cAT]

Originally Posted by rob67gmc

I don't really think I tracked down this link. More like I stumbled on it with some blind luck.

This harness came from the starter back toward the front of the engine, then split. One section went across the front of the engine towards drivers side and the other went towards the back on the passenger side, just below the fuel rail. The link was also on the same wire as one of the other links. Don't know why two links were on one wire. Still have no idea why it went bad.

up here in the rust belt the links that get exposed to road salt deicing chemicals get green/ corroded. possibly it was stressed by pulling on it or twisting when engine work was done.

thanks for the location of these . they should have these located in a common location with some box/cover for protection.