84 c20 Camper special, replace pick up coil or new HEI distributor

[robosmurf]

First post, and like most I'm having trouble getting reliable starts on my truck. It's some sort of a Frankenstein of an 84 c20 camper special that has the factory Rochester TBI installed.

I've been troubleshooting inconstant starts for a while after it died on me a couple months ago. I've replaced a lot of connectors since most of the clips are broken, swapped a ICM because I would be able to start my truck up and it would run until it was hot then shut off and no start until the next day. New fuel pump and relay were installed recently too.

I even took it for a drive around town but now I'm getting no start and no fuel at all.

I tested the AC voltage across the green and white wires off the pick up coil. I was only reading .5VAC. Would bad be dead flat voltage or is that enough to not trigger the injectors.

Is it a strait swap to put in an HEI distributor with vacuum advance and just find a vacuum source? It seems like with all the trouble of removing the distributor to replace the pick up coil I may as well upgrade.

[Irish_Alley]

did you swap the icm with a known good one or new one?
how are you checking for fuel?
before or after the injectors?
are the injectors getting the signal to "fire"?


im almost certain the signal for the injectors to fire comes from the pickup coil (could be wrong) but its at the base of the distributor and you have to remove the distributor to change it. i would try and find a know good distributor to swap it out. but report back before you swap anything out

[robosmurf]

did you swap the icm with a known good one or new one?
how are you checking for fuel?
before or after the injectors?
are the injectors getting the signal to "fire"?


im almost certain the signal for the injectors to fire comes from the pickup coil (could be wrong) but its at the base of the distributor and you have to remove the distributor to change it. i would try and find a know good distributor to swap it out. but report back before you swap anything out

New ICM.

 Visually looking at the injectors, I can fire them with a test jumper running from purple/white on the ICM connector to +12vDC off the battery, key on. It's a good spray when I test that.

I did just check voltage on the pink wire going into the coil and it's a good 12vDC but leaving the coil it's kind of a sketchy voltage. Like 4-7 vDC, that's only with the key on, I haven't been able to check while cranking yet.

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[Irish_Alley]

so how do you know its not getting fuel?

[robosmurf]

so how do you know its not getting fuel?

No spray when cranking

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[Irish_Alley]

oh ok. i saw you said "I did just check voltage on the pink wire going into the coil and it's a good 12vDC but leaving the coil it's kind of a sketchy voltage. Like 4-7 vDC, that's only with the key on, I haven't been able to check while cranking yet." thought you were talking about you havnt checked for fuel while cranking

[robosmurf]

The pink wire going from the remote coil to the plug on the ICM at the back of the distributor is the one with   the low voltage. I'm going to check all those connectors in the morning.  The splices are a little shoddy.

Should the pink wire all have good battery voltage when the key is on?

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[robosmurf]

It ended up being the pick up coil. Not as hard to replace as I thought it would be. I marked the distributor before I pulled it and had it back in less than an hour.

Trucks back running again.

[Irish_Alley]

what was your reasoning for replacing the coil? did you just go a whim?

[robosmurf]

I stuck a multimeter on it checking for AC volts while cranking. It was only reading .5VAC and wasnt going any higher.  I was using a troubleshooting guide that said it should go from .3-1.8VAC.

http://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/distributor-mounted-icm-tests-6


Since I knew I had good 12V going into the distributor, a new ICM that I assumed was good, and I could get the injectors to fire with a 12V jumper on the purple/white wire on the four wire connector off the ICM the coil was pretty much the only thing left.