I have an 86 K5 4x4 with a 350 crate motor. After having it for a few years I need to smog it in California (Original California car but was in Louisiana). Got the original E4MED CCC Carb (freshly rebuilt) on it and all the smog equipment back on it. When I start the engine it barely starts and backfires out the exhaust and the carb. If I disconnect the control harness from the distributor (which causes a code 41) the engine starts right up and idles smooth, but a little higher rpm than normal (about 1100 vs 700).
I have a code 23 that comes up (Mixture control solenoid circuit) The carb originally had a dual action solenoid that opened a valve to allow more fuel during cold starts. Difficult to replace so I replaced it with a standard solenoid. (If anyone knows the resistance of the aux coil, the plug that comes out the side, I think that would fix the code 23).
Any help would be greatly appreciated, I've pretty much hit a wall

 

By unplugging the distributor, you are putting it at base timing. If that allows the engine to start and run, then you should be looking at timing the engine again as it may be advanced or retarded too far for initial startup.

Why would you replace a component with something that is not the same...?

 

the simple answer for swaping th M/C solenoid is cost. You cannot buy a new one (they were only on 85-86 trucks) you have to send them in to get rebuilt which costs 200+. The standard MCS is easy to find and operates the same as far as the normal carb operation is concerned. The two that I came across both were bad for both solenoids.
I've set the timing to 6 btc, which is stock and it starts fine. Idles great still but when I plug the dist back in it will barely run. I'm guessing that the computer is attempting to adjust the timing, but I don't know what sensors it uses to adjust it. I guess the question is what are the sensors that give input to the computer that cause it to make the slight timing changes.

 

If the timing is correct, then it is likely a problem with your EST (electronic spark timing) module. This is what controls the advance.

 

I've replaces the module and it is still not working. I stuck a timing light on it with the distributor plugged in and anywhere from 12 degrees advanced to 8 degrees retarded. What sensor tells the computer if the timing needs advanced or retarded?

 

It is not just one sensor. It is a combination of sensors. The knock sensor tells the PCM when/if to retard the timing based on whether it senses pre-ignition. The throttle position sensor and MAP sensor tell the ECU what the engine demand and load are for proper timing. The coolant temp sensor also plays into this as the ECU changes fuel demands and timing based upon the coolant temperature.

Timing should be set by first disconnecting the EST connection at the distributor and running the engine up to operating temperature. With the engine at ~600RPM, set the timing to 8 degrees BTDC #1 using an inductive timing light.

Which piece did you replace? The module under the rotor inside the distributor, or the ESC module located to the passenger side of your brake pedal mounting bracket under the dash?

 

I replaced the ignition module under the rotor. I'll start checking for any obvious problems with the other sensors.

 

So to update still have the problem, just put it on the back burner. Noticed another issue as well. I cannot give more thah an 1/8th throttle without the engine Dying (This is all with the distributor disconnected to stay running, and yes I realize that there is no advance, we are looking at slow throttle). If i disconnect the mixture control solenoid then the problem goes away. I was also looking for an o2 sensor and couldn't find it or the wiring, any help would be greatly appreciated.

 

So after lots of searching I finally found the lost connector for the o2 sensor. the m/c solonoid when tested it reading a constant 55*. but still don't know what to do about the spark scatter.