I am chasing a misfire on my 1989 F-Body L98. Plugs, wires, injectors, cap, rotor, coil, etc. have all been replaced. I am getting down to the ICM now and I am confused. My distributor has a D1978 which appears to be for mid-90s TBI trucks. Rock Auto and AC Delco list the D1943a and D1984a as appropriate replacements. The D1943 has an installation note saying it is for non-HEI applications. I know my car has HEI ignition though it has a remote coil as opposed to the Corvette distributor which has the coil in the cap. The D1943A is also about $20 cheaper. Does anyone know which ICM is correct for my application?

 

1990 Formula 350 18k miles all original has a 369 GM ICM in it. At 18k miles take the cap off distributor and inside looks like something from the bottom of the ocean off the Titanic. Full of rust, white and green corrosion everywhere. Just about everyone of those small cap HEI distributors I've seen look like that inside in not much time or miles no matter how well kept the car or truck is. The caps should have had a vent on the top like the old Mopar V8 caps did. GM's design traps ozone inside the cap and eats everything alive in there.

Does your car still have the original Rochester Products Multec fuel injectors in it? If it does then they are bad. I don't care if they pass all tests and ohm out as good. They are bad.

 

I too have the rust collection under my cap & rotor. 7,000 - 8,000 miles.. pile of rust. Not sure why, but I need to pull the distributor to replace the pickup coil.

Our cars have the small cap HEI, while the Corvette's have the big cap HEI with integrated coil.

 

I just dropped in 8 new Delphi injectors from Southbay. I believe the 369 ICM is the same as the D1943A which says non-HEI. It seems Chevy only referred to the coil in cap distributors as HEI. I don't have a rust issue in mine but it is marked "remanufactured" and doesn't appear to be OEM. It has likely been replaced by previous owner recently.

 

GM saved a few cents by not vacuum venting the distributors. I have vacuum vented coil in cap HEIs, small cap HEIs as well as Vortec distributors. GM finally remidied their mistake on the later LT1s with vacuum vented optisparks but by that point they had millions of vehicles on the road eating distributor components.

 

I just stopped at the Chevy dealer and was told that these cars originally came with a 1917-9578 ICM which is the same as the D-1943A from AC Delco according to Rock Auto. The guy at the parts counter said the D-1984A does not show as compatible on his computer.

 

Check the ohms on the pickup coil, check for cracks around the reluctor rivits. There are screens on the bottom of my small cap HEI distributors. I have wanted to put a vac hose from them to the air intake.