zed-028

Well that was shortlived. just changed my rotor and cap on the 305 and it ran like a pig for a few mins then died.

Confirmed power to coil but no spark - changed coil out with a spare still no spark. Pickup coil reading fine. Done all the troubleshooting and it points at an ICM so i ordered a new one (only replaced about 6-8 months ago)

There is 1 symptom that ive never seen before and i was wondering if someone could shed some light on. The rotor is circular on top, when i pulled the cap after the car died, it had a 1mm crust of silver deposit on the rim of the circular edge of the rotor which looked like electrical component filings, it was hard as if welded to the top! Any ideas what this could be? Sound like a short?

RBob

iTrader: (1)

Check the rotor button in the cap. They are tricky to setup on the large cap distributors. I've seen them spin to the point that the heat melted the cap.

RBob.

ASE doc

You got the ground strap back in place under the coil properly? Without it, they won't run at all or not for long. Is there alot of end play or runout in the dist shaft? RBob is right that not having the button installed correctly is a big issue. The button goes in first, then the rubber seal, then the coil. You got your firing order right? Got #1 in the right spot?

zed-028

Sorry lads this is only a small cap with the coil thats a separate unit. There isnt a ground strap however ill be grounding the ICM with a ring terminal this weekend when i get the time to look at it.

being a separate coil setup its grounded through the mounting hardware to the engine. very odd situation and ive never seen it before.

Also... these cars are really hard to push for long distance... calves are killing me.

ASE doc

Wide low profile tires don't push easily.

Sorry, I misunderstood what dist you were dealing with. I remembered the 87 carb engine having the internal(large cap) HEI. As RBob said, recheck the button in the cap. It's spring loaded and it tends to break if you aren't careful to set the cap down straight over the rotor. Be sure the rotor is slid all the way onto the shaft. The shaft will rust and become rough. I use scotch brite and shop air to clean it, then apply a light coat of dielectric grease before installing the rotor. Look for excessive runout or end play in the shaft. Check the gear for wear by checking how much you can rock the shaft back and forth. It should have very little free play of any kind.

Did you disconnect either of the two connectors from the ICM? Make sure the connectors are fully seated and no bent pins. How did the coil tower look? Was it corroded and deteriorated? Is the wire firmly connected? The ICM is grounded through the brass rivets that extend through its plastic body. It doesn't require any further grounding. If the mounting surface or fasteners are corroded or rusted, you need to clean them. Be sure to coat the mating surface of the ICM and dist body with heat transfer compound. It's a white substance that comes with a new ICM. Dielectric grease will also work.

The ICM is a high failure rate item and very difficult to test reliably. The bench tests performed at the parts store, or that can be done with a DVOM, is only valid for determining if the module is dead. It will not point out an intermittent failure. The pick up coil is also a common problem and can be tested for resistance.

In addition to the dist itself, there are the circuits to the ECM that provide crank reference and EST operation. You will need a good service manual with testing instructions and a DVOM to test those.

zed-028

Thanks mate,
yeah ive been through the EST circuit before with bad EST grounds, no ref pulses etc. so im just trying to get this thing running again until i get the new dist in a month or 2 (the other thread youve been commenting on ) seems that the ICM was again the issue, i hate these little things. thats 2 in 18 months, we have some hot weather here in australia (40C plus) throughout summer but both times they have died at the end of our winter/beginning of spring. good times.

ASE doc

Two things to look at when you have repeated ICM failures. Ohm test the coil primary. Be sure it is at least .5 ohms. Service spec is between .5 and 1, I like .7+ better from a stock coil. Low primary coil resistance will stress the module.

Be sure again that the base is clean where the module mounts and that you apply dielectric grease to the metal base of the ICM. Be sure the fasteners are clean and screwdriver handle tight. Check the pick up coil. Service spec is 500-1,500 ohms but 800-1000 is better. Be sure the power supply from the coil batt+ terminal is good. Install a good quality part like AC Delco or Standard Motor Products.

senior bear

whot dus the inside of cap look like has rotor been rubbing on it ? have you tryed puting old ons back and c if that cures problem .are parts identical to ons removed ?

zed-028

catastrophic magnet failure - replaced distributor and it goes like a rocket. also helps that i ditched the cc q-jet and then rebuilt a unit from a 73 pontiac on there.

zed-028