Just when I thought my car was finally working, it's thrown another curve ball.

Car is an '85 L69 with stock ccc qjet etc.

Drove out to do some coronavirus-safe shopping and the car threw a CEL. Last time I drove it, it started stuttering slightly at part throttle. So I unplugged the battery and let it reset, thinking it might be something to do with the self-learning ECM.

Next time I went shopping, it threw another CEL within a couple of miles. At the supermarket it cut out, but restarted and idled. While idling in a queue, a mysterious, brief puff of white smoke emerged from the rear of the passenger side of the bonnet hood. I did what all people who drive old cars do - I ignored it and pretended nothing was happening.

Next day I go to get the trouble code. Turn key, and there's no clicking from the Mixture Control Solenoid. I bridge the A and B terminals on the ALDL port and get just a solid CEL, no code 12, nothing. I'm guessing that puff of white smoke was electrical. I couldn't smell any burning though, neither inside or outside the car.

I've pulled the passenger side arch liner out and the passenger side kick panels. I can't see any obvious burnt parts in the loom, but I haven't dug it all out yet. My plan tomorrow is to pull the ECM out, open it up and see if I can find any burnt components. I have a spare ECM on the shelf, so I might just swap that in.... but I don't want to risk damaging it.

Does this smell like a fried ECM to you guys? What would cause an ECM to fry, anyway? Do these things just happen, or is there always a cause?

Cheers all,

ND

 

Actually , from here across the pond I can't smell much of anything , but were I forced to guess I'd be looking for a short circuit in the wire bundle leading from the engine to the ECM (which passes right through the area where you saw the smoke) . Also of note here ; when the ECM circuits experience a short circuit there is a fuse mounted under the hood in and about the area of the righthand fender that gets blown , this will likely need replacing after you find out what let out the smoke (melted wires are a good sign of where the overload/short circuit are) ......

 

Check the ECM IGN fuse.

 

Thanks for the suggestion of checking the engine bay fuse for the ECM wiring - I had no idea it was there! I spotted it and checked it and found it was ok.

Sofa, you're right about the ECM IGN fuse - that had tripped. Nice to think that little fuse probably saved my car from burning to a crisp!

I pulled out the ECM and checked that too, but it looks completely fine inside, with no evidence of heat damage at all.

I started pulling the ECM loom out in to the engine bay, but found the blower motor seemed to be blocking the inner fender hole just enough to stop the pass-through connector getting into the engine bay. Typical! I'll have another fiddle with it all in daylight, and then resign myself to having to pull out the blower motor! Hmph!

 

Just to add a bit of potential experience with the lovely CCC, I had found my MCS would randomly not work (and SEL would light in such cases as appropriate). After I checked and replaced almost everything (ECM included) I found out it was the MCS itself that was bad. It would work for a period of time, then cease, and throw a code (I forget which off hand), then maybe the next day work again. So just know if you fix up all your wiring and whatever event caused the fuse to blow, and keep getting a weird "sometimes it works and sometimes it doesn't", definitely don't count that little bugger out. I put back my original ECM, with a new MCS, and have put a few thousand miles on it since with no more codes or related failures.

 

I thought I'd updated this, but I haven't. I was reluctant to tear into the ECM loom as it showed no evidence of heat or damage, and I'd have thought something would be visible even through the loom covering if enough heat had been generated to make the wires smoke.

I did however discover a wire in the engine bay that had got very hot - melting itself to adajcent wires and melting the loom covering. It's a three way junction between green wires, leading from the fan switch to the relay and I think to the throttle kicker. I cut this out, soldered it all neatly back together with heat shrink and checked the wiring diagrams. Nothing to do with the ECM IGN fuse. Replaced the fuse anyway and started the car. Fuse didn't blow, the MCS clicks (thank goodness!).

I can't figure out how the fan switch wiring could possibly affect the ECM IGN fuse, so I'll guess the problem still persists somewhere. My next best guess is it's the PNK/BLK wire that runs behind the dash to the fuse board - the blower motor does some funny things (still runs with the ignition off) so I'm guessing some oddness is back there.

However my car doesn't idle any more. No codes thrown. It was stumbling before the ECM IGN fuse blew, I thought due to crappy Supermarket petrol but that's probably wishful thinking.

After five years of trying, I'm starting to wonder if this car will ever actually work.

 

I thought I'd drive the car a few more times before updating this - I've since done a couple of hundred miles in the car.

I'd seen a random suggestion online that a shot of redex can cure low-quality petrol. It seemed a long shot, but I had a bottle handy and it seemed worth a go. I chucked it in the tank and left it a week. My plan was to start the car, back out onto the driveway and leave the engine running on the fast-idle cam to give it the best chance of staying alive long enough for the redex'd fuel to reach the engine.

The car started and ran quite badly, sounding very rough and quite clearly missing. It sat there chugging away on high idle for several minutes until, suddenly, it calmed down. Tentatively, I gave the throttle a tap and it dropped off the high idle cam settled down to a steady base idle. I cautiously took the car for a spin and it ran perfectly.

I noted the oil level was very high - I guess with the MCS frozen a lot of petrol was simply washing past the piston rings into the sump - so I changed the oil. I've since the driven the car several times over a couple of hundred miles and it's hardly missed a beat.

Was it that simple? Just bad supermarket petrol, cured with a bottle of Redex?! I could do with a break with this car!

The ECM IGN fuse hasn't blown again either. Fingers crossed for that one...

 

To say that the General Motors "CCC QuadraJet" program was a "Horror Show", would be an understatement.

The bottom-line is that GM QuadraJet had to be phased-out completely, as Electronic Fuel-Injection was quickly becoming mandatory based on US Government regulations.
The "Computer Controlled Carburetor" variants (E4MC, E4ME, E4MED, and E4MEF) were only supposed to be a BULL-**** way of keeping a more affordable carbureted engine option available, until less expensive EFI systems were ready for production (TBI for example vs TPI).

Both the Electronic Engine Control Modules and CCC Quadrajets were far to simple in their respective designs to ever achieve long and well running/ performing engines in terms of drivability/ reliability.

I won't go into detail... I will just say that GM knew this system would never be successful in what it was supposed to achieve...
It was just a BULL-**** Temporary Stop-Gap before they could get "Throttle-Body Injection" finalized for production.

When the early non-CCC Quadrajets were new or kept maintained they actually operated very well for what they were (a economical 4BBL that could perform if provoked).

But the CCC Quadrajets, even when new or maintained, never were what their non-CCC counterparts were.
They could be temperamental or work perfectly depending on conditions and the very limited parameters that the control-logic/ monitoring-logic could use.
Sometimes, wanting one of these CCC units to operate properly... was like asking a blind pilot to land a plane perfectly.

There are many threads here on TGO and else where, regarding modifying the CCC Quadrajet to help it be more controllable and reliable.
I would do some research on this... look into removing the tamper-plugs that conceal the mixture-screws in the front of the base-plate; among other methods of manually tuning the carburetor.

Good luck and have fun!