Neerclass

Hey there person who I assume is furiously pouring through TGO trying to find a solution. Recently, my '91 3.1 v6 left me stranded and as I've done a million times before, I came to TGO. Searched. Found arguments and theories. Throw this part at it, that part at it. Test thing A, you're supposed to be doing it this way B, have you tried C? So what I'm going to do here is go through a comprehensive list of everything I did. Everything. That eventually, after a LOT of frustration, got my car back on the road. I hope this helps you. Here we go.

Symptom: The car just stopped. No preamble. No drama. It just STOPPED. Like it ran on A/C power and someone pulled the plug. Now it just cranks but won't even try to sputter to life.

Part 1: I BET YOU ITS THE ICM. ITS ALLLLLLLLLLWAYS THE ICM.

By now, I'm assuming you've done "the paper clip trick" to pull your codes and what you've found is... nothing. Code 12. What does it mean? Exactly nothing in your case beyond the little sliver of good news that there's nothing else wrong with your car. Code 12 we'll call a "baseline code". It just means for you that the car is off, the ECM can't find anything wrong other than its off. It's good/bad news. Because it also means that the ECM can't save you with a convenient trouble code to throw a part at.

In my case, in a LOT of cases, what happened to you is that your Ignition Control Module (ICM) failed and if you're lucky very UNLIKE me, that's all. Your ICM is located directly underneath your distributor cap. It comes out with two phillps head screws, easy peasy. Although to you'll have to move your dizzy cap out of the way and kinda maneuver your way around to get it out. Nothing too-too hard, but if its your first time, just pack your patience. Once out, your local AutoZone/Advance/O'Reilly's can test it for you. The test only takes a minute. Now here's an important fork in the road.

Q: Is your distributor original or have you replaced it recently?

A 1: Original? Then replace it. The whole thing. Don't bother trying to salvage it part by part. You'll just make it worse trying to salvage a 30 year old part.
A 2: New? Great! Then you just need a new ICM!

In either scenario, your ICM failed either BECAUSE it was original, or because the dandy new dizzy you bought (probably DuraLast) doesn't come with an ICM that's... great. To tell a quick story, in going to my local and trusted AutoZone with it's super friendly and amazingly patient staff, I asked them to test the Duralast ICM they were gonna sell me. Guess what? Straight out of the box, it failed. The ValueCraft ICM they had? That failed too. The woman helping me then proceeded to call the store down the road, the store half an hour away, AND the HUB store on the other end of Philadelphia from me, and guess what?THEY ALL FAILED. Six ICMs between two aftermarket brands, three different stores, miles apart, and they had a 100% FAILURE RATE. So, here's the hard part that you're not gonna like. No questions, no arguments, and no negotiations, YOU HAVE TO BUY THE AC DELCO ICM (Part #D1984a -or- #D1943a). Which means that if they don't have it in stock (brace yourself, they likely won't), then you'll have to wait at least a day. Anything less and you're gambling on this happening again.

So in the meantime, unless you're buying from Amazon, you'll need to take a trip to your local Best Buy or MicroCenter if there's one near you because you're going to need GOOD thermal paste. The kind that you use to marry a CPU/Processor to its heat sink. If you've snagged it from Amazon, just tack it on to your order so you have it all at once. Arctic Silver 5 works well Thermatake or the Insignia brand that they sell at Best Buy work just as well. Heat is what kills an ICM dead and these things are simply put, not made well. They're made to live inside the dizzy, sure. But you can toast one just by looking at it funny. So invest in a tube or two of thermal paste. Some if not most ICMs come with Dielectric Grease or Silicon Thermal Paste. Don't bother with it. Both bake under pressure and after they harden, they may as well not even be there.

So, moment of truth. Was it your ICM? Yes? Awesome. Happy motoring. No? Keep reading.

Part 2: Everything BUT the ECM is suspect. (Injectors)

Read it again. It's NOT your ECM. Your ECM would tell you if its broken. Or at least it'll try to. Check your tach when you're cranking. Is the needle wiggling? Good. That means your spiffy new ICM is doing its job. Buuuuuut its still not starting, yeah? I'm sorry, but hang in there. So, what else? Well, next, and this is gonna sound weird... pull your oil dipstick and smell it. Does it smell like gasoline? No? Good. Move along to part 3. Yes? You have a leaking injector. One or multiple of your injectors is stuck open and is dribbling liquid gas. Which one? Welllll... it doesn't really matter. If your injectors are original, you have two options. Get a set from South Bay Injectors (great affordable set) or get the Accel set. I personally replaced my South Bay set with the Accel set. If you've been searching around, you'll see plenty of posts about Accel having hit or miss parts. But from my experience, their injectors are fine and well reviewed. Lube up the O-Rings with vaseline, slap 'em in.

Also, while you're here, check your Fuel Pressure Regulator. If you've never replaced it, take the little vacuum hose off of it and smell it. Does it smell like gas? Its not supposed to and that means the diaphragm on it is shot. Get another one.

Now is also a good time to check your plugs. You've been futilely spraying them with gas and they're likely fouled by now. If you haven't changed them in a while, get new ones. If they're still new-ish, pull them, get a torch and blast them with heat to de-foul them.

Start or no start? No start? Part 3 it is.

Part 3: What the hell is an Idle Air Control Valve?

I dunno...

Okay, I DIDN'T know, but now I do. It is what it sounds like. When you're idling, the ECM commands this Idle Air Control Valve (IAC) to open and close in your throttle body/plenum... the criss-crossy plate thing sitting on top of your engine with the fat snorkel and all the bolts in it, so that if the ECM decides you need more or less air to maintain a consistent idle, you get it and don't stall. And guesssss what? Yours is 30 years old. You could clean it, BUT ITS 30 YEARS OLD. JUST REPLACE IT. At this point, I'd cleaned mine and glory day, the car started and ran. For 10 minutes. Then it left me stranded just a block away forcing me to push the car back home, much to the sadness of my neighbors who obviously have money on me either fixing it or not fixing it at this point. So. You buy a new one. Additionally, if your EGR valve is original, it might be time to replace that too. Even though EGR problems throw a code, elimination of future problems can keep you a happy F-Body owner for a long time.

You'll need a torx bit set to remove and install it. Harbor freight sells a complete security bit set, Torx included, for $9.99. Be gentle with installing it. Use a screwdriver/bit-driver, not a ratchet. Aluminum and torque are bitter enemies here.

After you've installed it, you'll have to do the paper clip trick again because this is one of the only non-plug-and-play parts on the car, surprisingly. Paper clip the car into diagnostic mode (KEY IN, ON POSITION, ENGINE OFF) and wait 60-75 seconds. This will fully extend the plunger on the IAC. After that, pull the plug out of it. It's ready for the ECM to take it over. You can search for the full procedure on calibrating an IAC, resetting your idle, etc. But if your idle was fine before, then this is all you need to do. Shut the car down, pull your trusty paper clip. Plug the IAC in and give it a try. Start? Great. No-Start? Alright, lets get to the last, most simple, and really stupid part...

Part 4: Buzzword of the day is... Distributor Cap.

My dizzy cap had a split in it. I've replaced tons of them. And never the rotor at the same time and I've been fine. Bad practice, but not the worst imaginable. So I bought an AC Delco crap cap and no rotor. This was a mistake. Because after I'd gone over MORE than everything. Had my Ignition Coil tested and bought a new one anyway. Checked continuity in the wires between the ICM and the Ignition Coil. Checked my pickup coil and Ignition coil wires with a Digital MultiMeter. Checked EVERYTHING. I still had no spark. I had fuel pressure and nothing to ignite it. I was frustrated, exhausted. I was working on this nonstop for two and a half weeks. And then I noticed something in just catching the slightest glance at the inside of my new Delco Dizzy cap... the carbon button looked weird. Not weird, but... not right. So I checked my original and yeah. That looks..broken, maybe? So I do some looking and some reading. There's nothing to tell me whether is really broken or not, but I'm willing to take a chance, since its a cheap gamble.

I go to Advance, get the brass terminal BWD Select cap (#C244, DO NOT LET THEM SELL YOU #C244P), and a BWD Select Dizzy Rotor. Slap them in and BAM. Car starts. I found the broken piece of my brand new AC Delco distributor cap's carbon button rattling around the top of the old rotor. Somehow. Maybe centrifugal force kept it there like a carnival ride. I don't know. But BAM. Car started and has been happy and healthy since then.

In Conclusion

Hopefully, by the end of this, your car has started. I wanted to consolidate my personal experience and the hours I spent searching around and reading through TGO in hopes of creating a procedural method to reference when the problem seems impossible and nothing's working. I encourage members to add to this, link other posts with relevant information, and hopefully, the next person who has this kind of failure, cascading or singular, won't have to spend as much time as I did trying to fix it.

I'd like to thank ALL the members of TGO for always being so willing to help and be sounding boards for all manner of problems. And please, please, please, whenever you have a post and people are helping you, once your problem is fixed, COME BACK AND TELL EVERYONE HOW YOU DID IT. Too many troubleshooting threads go dead without a solution and you could really be helping someone out in the future!

Happy motoring,

~Neer

zs&tas

Nice ! Thanks for taking the time

Gfunkill

nice write up. Been there, done that, never thought enough to make a post though.
Your writing style sounds like KED85 that wrote the "3.4 swap boogie" article.

Sierra6

i had a similar situtiation when I thought my ICM was bad. it would crank the car but the car ran badly once warm. when I took it off, I took it to two different auto parts stores. it tested bad at advance and tested good at orielly's. and neither of the two replacements I bought would even start the car. so I put the old one back on. My problem ended up being a bad wideband sensor (I'm running megasquirt II). I fear the day I have to find another working ICM though.

Sierra6

And I also recently had a broken dizzy cap too. is the C244P more prone to breaking? or does it not fit? what's the difference?

Neerclass

There's technically nothing wrong with #C244P. It's just a CarQuest reproduction of the AC Delco OEM basic cap. But in my experience, if you ask for #C244, their system search shows #C244P as "recommended/best" in the drop down FIRST and without protest, that's what the associate WILL grab for you, or if they don't have 244P in stock, they'll tell you that they don't have 244 AT ALL and send you to another store for a cap you didn't even want in the first place.

#C244 is specifically the BWD Select/Premium brass terminal cap. And stranger still? It's LESS expensive than the CarQuest/Delco basic cap for whatever reason.

TomP

Really nice write-up! Agree w/Gfunkill, your style did remind me of KED85 (RIP). Agree too about getting an original AC Delco ignition module.

I wanted to add another one that you hinted at-

EGR valve without throwing a code- I recently helped a friend of mine with this on his 2.8 S10- it brought back some memories!

If the EGR valve is old, it can corrode (carbon/rust) and get stuck in the "open" position- and if it's stuck open, your engine wont' start. Check the EGR by (on a cold engine) putting your fingers underneath the valve- you'll feel an opening; the valve should be bottomed out, not stuck high up.

This could also cause a "stalls when hot and coming to a stop" condition. EGR activates > 40 mph with hot engine- and if you come to a stop and the EGR is stuck high, the motor will stall- and the vibration (of the stall) can shake the EGR loose so it falls shut. Rinse and repeat... until you change that old carbon'd up rusty EGR.

Does Accel still make a brass dist cap/rotor? It used to be spec'd for the 4.3 Vortec v6's...