I feel like I'm blowing up the carburetor forum lately but I can't seem to find the info I'm looking for through a search - my apologies.

I recently rebuilt my factory Q jet on an 87 LG4 and started it up for the first time last week. I haven't adjusted a thing on the carb yet, but the car runs and drives. I took it for a 50 mile spin and it seemed to do pretty good! Bit of a lousy idle but that'll just be some fine tuning. My question is this:

I'm getting a code 23 and I don't hear a click when I turn the key to ON. It takes a bit of feathering the gas to get her to idle up, but the car does run and drive pretty well from what I can tell. The carb was decently fine before I tore it down but it was leaking all over the intake and I was getting run-on pretty often so I figured it was time for a rebuild. Why wouldn't I be hearing a click when I turn the key though? I haven't set the dwell yet, but are there other problems I should be looking at before I start going in and making adjustments? I know code 23 is a bad MCS circuit but I don't know if that's synonymous with "bad dwell set" or "your MCS is totally cooked, dude."

As a side note, when I adjusted the MCS, I didn't use the ruler included with the kit - didn't think of it - I just measured a total of 1/8" travel using a standard ruler and a secondary metering rod as laid out in the sticky up top. Is this an issue? The IAB was reset to about where it was when I pulled it but as I said, I haven't adjusted dwell yet so this will definitely be the first thing I do.

Any insight you guys have would be much appreciated!

 

Don't "adjust" ANYTHING until you find the problem and fix it.

Anything you "adjust" while it's broken, means that the adjustment will be WRONG when the non-working stuff is restored. Therefore it means that all you accomplish by putting your d*** skinners in there, is to create extra work for yourself.

You say you haven't "set the dwell" yet. What IS the dwell now? Is the ECM actually telling the carb to do anything at all? Are the wires going to it broken, disconnected, or shorted together?

Code 23 means that the MCS is either open (disconnected) or shorted. It's not about "setting the dwell". Could be the wiring outside the carb, or the wires inside it, from the connector to the solenoid itself. (pinched between the castings for example... that would probably be my first guess)

Find the problem FIRST before "adjusting" ANYTHING.

 

Hm, I haven't checked the dwell yet because as you said, I didn't want to adjust anything before taking care of the code 23 and having the check engine light go out. I just wasn't sure if, for example, when rebuilding the carb, it would be possible to adjust the MCS SO out of whack that it would throw that code even though I thought I did it right. What I understand is that this code is purely the result of an electrical issue and not the result of an adjustment issue? It was never on before, so I must have busted something during this process. Oh what a pain!

Are there any suggestions where I should look if pulling the airhorn off and checking for pinched wires doesn't yield any results? Before I pulled the carb off it was fine.

Thanks!

 

I said CHECK the dwell, not ADJUST it.

By checking it you'll find out whether it reads something normal-ish, in which case the ECM is working fine and thinks it's trying to control the MCS but the plunger is physically restrained somehow (not likely); or maybe it reads 100%, in which case the wires might be shorted; or maybe it reads very high but not quite 100%, in which case the wiring between the ECM and the MCS is likely disconnected; or maybe it reads 0%, in which case the ECM's driver is open (not as likely but still possible).

In any case, you'll gain insight into what's going on.

You are correct, code 23 is electrical in nature and is NOT the result of an adjustment issue. It means that the ECM is not seeing any current flowing in the MCS circuit. IOW, that either it's disconnected (broken wires etc.), or all the current that passes through the MCS and SHOULD be going through the ECM driver is instead taking some other path to get to ground (pinched wires). You have some form of electrical issue.

You can also check to see if, when the ignition is turned On, if the plunger moves. Shorted wires would make it pull in (go down) immediately and stay there. Then it will retract when the ignition is turned Off. Disconnected wires will make it stay in the retracted (up) position at all times. I usually use a small tie-wrap or one of those plastic straws that come on spray cans for this test, something light enough to not disturb its normal action.

Obviously there's things to look at that don't take much effort but will illuminate the situation at hand.

 

Thanks for your advice! Turns out a couple things were happening. The MCS wiring was pinched against the body of the carb causing a no-read condition AND was tightened so far down that the plunger couldn't even click with the key to ON.

Took it off, made the adjustments, and everything went away.

Now I just have a rod knock that developed after putting the carb back on that needs addressing.

I'm just going to shove this thing into the Hudson River, I swear.

 

Alright! Update - Kind of.

Good news - Wasn't rod knock. It was my 30+ year-old catalytic converter barfing up its internals out my exhaust. Straight piped it and we're good to go on that front.

Bad News - I still can't get this thing running properly and my mechanic simply refuses to touch it, so it's all up to me.

I got the MCS/Check Engine situation taken care of with that pinched wire and the light went away for a while. Got it back from the exhaust shop and it was still idling around 1000 in drive, so I got home, popped the hood, TRIED to adjust the idle down with the IAB screw, but no dice. Still idled 1500 in park. So I shut it off (with lots of dieseling to boot). Started it back up and code 23 is BACK, BUT it idles better now (around 600 RPM) than it did with the check engine light off and the MCS operating normally! What is going on?!

Why would one drive home cause the MCS to fail like that when it working fine a minute ago and WHY would it idle lower with the MCS inoperative than with it operating properly?

This is driving me insane and I'm thinking of just sending it off to Cliff's High Performance and not having this thing for the summer (which is what I bought it for) but I feel like I'm so close and don't want to give up!