Which Delco ICM for a Formula - d1943a or d1984a? Thoughts on TFS distributors? (Page 1/3)
echocharliepapa JUL 19, 10:29 PM
GM's parts site (and everywhere else) seems to list the d1984a as the proper replacement part # for the Formula's ignition control module, although the d1943a is the one listed for all the other '88s with the 2.8L v6. The only difference I can see between the two parts is that the d1984a is more expensive and the d1943a is "w/o HEI". I haven't been able to figure out exactly what that means-- is it a feature of the ICM or a feature of the vehicle's overall ignition system that needs to be compatible? My understanding was that the Formula is just a GT with notchback styling (and less options included by default, but still available).

On a related note, does anybody know what brand parts the Fiero Store's distributor ships with, or have an opinion on it (or other vendors' "complete" distirbutors)? I'm looking at probably needing to replace the pickup coil in addition to the ICM, and might as well get a new cap and rotor while I'm at it, so just buying the whole assembly is looking like an attractive option.
echocharliepapa JUL 19, 10:42 PM
FWIW, I'm getting a code 42, car now won't start, but started the other day (from a jump after stalling out halfway down the block) and drove for ~50 miles throughout the day. Last week I replaced a leaky heater core and flushed the coolant, did spill a little antifreeze by the thermostat housing when filling it back up, but have had the code 42 for longer than that. I tried to check the ignition system with a multimeter per those instructions that are floating around online, I think the ICM is definitely bad but the whole distributor assembly is looking sketchy. The holes for the mount/ground screws, and the connectors between the ICM and pickup coil were corroded as seen here:


And the rest of the pickup coil is not looking so great either (looks like the connector clip is disintegrating too):


Just trying to get this all done correctly in one go so I can get my workhorse back on the road. Obviously money is an issue, but I am willing to spend what it costs to get it done right.

EDIT: and yes, the ICM I removed is made by Standard, not AC Delco, which is why I'm not sure which part # to get to replace it with.

[This message has been edited by echocharliepapa (edited 07-19-2022).]

Patrick JUL 20, 03:41 AM

quote
Originally posted by echocharliepapa:

...the connectors between the ICM and pickup coil were corroded as seen here:

CLICK FOR FULL SIZE



IMO, those corroded terminals alone could be causing all your issues. Clean them up, put some dielectric grease on them, put some fresh thermal compound between the ICM and distributor base, and see what happens.

The surface rust inside the distributor is normal. It's caused by the ozone being produced by the high voltage inside the cap. Your distributor looks pristine compared to how mine looked years ago.

PhatMax JUL 20, 07:55 AM
Doesn’t even look like there was ever thermal paste on it. Looks like the magnet is cracked too…..more than likely it wouldn’t idle right.
Card one made a new…not rebuilt, distributor that was complete and the magnet portion is improved. I bought one from Rock but now I see they only have rebuilt ones…but they are improved.

https://www.rockauto.com/in...301633-bot__ra_p.jpg
echocharliepapa JUL 20, 01:14 PM
So a little more context, I have been having some overheating problems too, both leading up to the heater core replacement and following it. Tons of nasty crap in what I had drained-- and caked on the inside of the overflow bottle-- leads me to believe someone had gunked up the coolant system with stop-leak which caused a blockage in the heater core that allowed pressure to build up and the car to chronically overheat until it sprang a leak. After clearing all that out and putting the new core in, I didn't notice at first that the seal on the radiator petcock was deformed, because I put the stem back in blind reaching under the car after I had flushed the system with water. It didn't feel right by touch, but it was holding fluid without dripping so I stupidly thought it was fine. That caused it to dump most of the brand new coolant I had put in it all over the road once the system was under real pressure and not just being burped in my driveway. I limped the few miles back home a couple hours later, but it got dangerously hot while I was trying to get it to a safe place to park first. The lesson I chose to take from this experience is to check *everything* when working on a particular system and replace anything iffy.

Anyway, I figure all that extra heat (in the middle of a heat wave here, too) finally killed the ICM that had already been acting up intermittently beforehand. There was a *touch* of thermal paste on the underside of the module, but it looks like it was the clear stuff, and it was not spread evenly. This car is a survivor not because it's been well-maintained, but out of sheer stubbornness. I've decided to stop taking it to other people to have work done, unless it's something I don't have the tools or garage capabilities for. It may sound like I'm an idiot who doesn't know what he's doing and is going to ruin this car, and that may be true, but I think at least the fact that I care about it (been in my family since the early 90s) makes me a better person to have working on it than a tech who wants to get it rolling out of their shop so they can move on to another vehicle. I try to pay attention to how it operates after I've done work, I just don't always know what to look for. I am hard on this vehicle, it has been a food delivery workhorse for most of the decade or so I've owned it, but I also try to address issues when they arise if I can.
Patrick JUL 20, 03:05 PM

quote
Originally posted by PhatMax:

Looks like the magnet is cracked too…



I'm curious, where do you see the crack?
ArthurPeale JUL 20, 03:11 PM

quote
Originally posted by Patrick:

I'm curious, where do you see the crack?



Right in front, in the sandwich. It a tiny line, if that's what they mean.

on my GT I didn't mess around, brand new Cardone distributor. It's got nearly 40 years of wear and tear that's not getting better.
Patrick JUL 20, 04:18 PM

quote
Originally posted by ArthurPeale:

Right in front, in the sandwich. It a tiny line, if that's what they mean.



I saw that, but thought it was perhaps just a speck of darker rust.

If there's a tiny crack in the rotor magnet, I wonder how that actually affects its function, if at all?
css9450 JUL 20, 05:12 PM

quote
Originally posted by echocharliepapa:

And the rest of the pickup coil is not looking so great either (looks like the connector clip is disintegrating too):




On mine, that plastic clip was so disintegrated it had broke in half and got lost years earlier. Those two wires were attached to the module just by the little metal tabs! Sort of friction fit. Eventually I started having issues and while attempting to investigate, I realized the two wires were so faded and burned (by the ozone?) that I could no longer even tell them apart. Time for a new pickup coil!

PhatMax JUL 20, 07:26 PM
If there are many cracks it will make a difference. A mechanic I used to deliver parts to had a 88 that they could not figure out why it ran so shitty… he replaced so much stuff, entire exhaust, complete tune up, numerous sensors….finally a year later they replaced the whole distributor and it ran like new.. I seen the dist…the magnet had a ton of cracks. I have two spare dist and both of them were cracked.