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Mixture Control Solenoid

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by johnny reb, Jan 2, 2003.

  1. johnny reb

    johnny reb 1/2 ton status

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    The mixture control solenoid on my Quadrajet doesn't have anything plugged into it. Since I've owned the truck there has never been anything plugged into it. I'm having trouble with strong exhaust fumes and I thought I'd start with the carb. Should the solenoid be plugged into something?
     
  2. imiceman44

    imiceman44 1 ton status

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    If someone changed the distributor from ESC model to older HEI model, you will not need the Carb plugged in.
    If it's still stock then you need to find the plug and plug it in.
     
  3. imiceman44

    imiceman44 1 ton status

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    OH are you talking about the air conditionning solenoid which raises the idle speed when it engages? then no it doesn't matter unless you have AC on.
     
  4. johnny reb

    johnny reb 1/2 ton status

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    As far as I know, the HEI distributor is stock on my 1986. I had the old 305 replaced with a 350 about 2 years ago. Ever since then, there has been no plug in the mixture control solenoid. Much of the old emissions equipment was removed at this time as well (ie, air pump) so I could get the headers put on. I've looked for a plug lying around in the engine compartment but I can't find anything that resembles a plug that would fit in there. I guess what I'm trying to get at is: would the mixture control solenoid being unplugged lead to increased exhaust fumes?
     
  5. imiceman44

    imiceman44 1 ton status

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    I would replce it with a regular carb or if you can just replace that part with a mechanical.
    I haven't worked with those on mine but i had a four cylinder GM (OPEL) and I replaced it with a regular idle mixture screw and it worked fine.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    This is the plug on the passenger side?

    I would be willing to bet "failure" mode (as in no power) lets that thing work as a "normal" carb. I'd have to look at the manual to see exactly what it does, but I'm pretty certain it only lets the carb run with so much enrichment under operating temperature. Kind of a dumb idea IMO, it's basically a choke run off of coolant temp.
     
  7. Itali83

    Itali83 1/2 ton status

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    I'm in school now and we just did rebuilds on the E4ME Quadrajet carburators like the one you have on your truck. Those carbs are designed to be linked to the computer to control the air/fuel mixture. If the solenoid becomes unplugged or the computer fails, the soleniod is open at rest. Open = rich mixture. so with the mixture control soleniod being unplugged, it is running at the richest the carb can run, so I would definitly find out why it's unplugged, and if the computer system has been tampered with, I'd just put a fully mechanical carb on it.
    Ben 87 Jimmy + 89 Blazer
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  8. johnny reb

    johnny reb 1/2 ton status

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    Yes, this is the plug on the passenger side. So the rich mixture is probably why I'm smelling the strong odor of fuel. Like I said, I can't find the plug for this. What other options do I have to get this working properly? From the plug on the carb, where does the wire go?
     
  9. Blazer1970

    Blazer1970 1/2 ton status

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    Are you talking about the electric choke plug? I thought we determined a while back that they did not use electronic mixture control on the truck engines. Does your engine have an oxygen sensor? If the choke is not plugged in, it will never open, and you will run really rich all the time. The colder the ambient temperature is, the tighter the choke will close.
     
  10. Itali83

    Itali83 1/2 ton status

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    The wires that plug into the mixture control soleniod should run into a harness and back to the ECM. It is controlled by the ECM so the wires run right from it. There will only be 2 wires for the soleniod. SO I would look for a wire harness that comes out of the firewall on the pass side, and look for two wires that are just hanging,cut,melted or something and those will probably be it. But this is definitly what is causing your rich condition.
    Ben 87 Jimmy + 89 Blazer
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  11. dyeager535

    dyeager535 1 ton status Premium Member

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    The problem is, these trucks used THREE Q-jet versions in '85/86 based on destination/GVW. (apparently)

    Just because a Q-jet has an electrical plug does NOT mean it is CCC, ECM, Feedback, whatever you want to call it. If it doesn't have TPS and O2, it likely won't have an ECM. ESC yes, but that was standalone before injection, except *probably* on TRUE CCC equipped trucks, which are apparently quite rare.

    You are correct that a true CCC carb will run full rich in "fail" mode, but a one plug Q-jet does not operate the same way as far as I've been able to discern, it's still got a power piston that is vacuum controlled, but is limited during warm up.
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Sorry I didn't attack this directly already.

    If your carb is set up like I think it is, then I kind of doubt the smell problem is with the electrical plug, although of course, as with everything automotive, it could be.

    Assuming the odor is coming from underhood, and not the exhaust pipe, I'd check and make sure that the carb isn't spewing fuel when its running. I had a Q-jet that had an incorrectly set float, and the gas smell was quite strong. Once I pulled the air cleaner, and saw that it was full of gas, I knew what the problem was.

    If you can't find the plug though, someone must have cut it, or the carb isn't original to that engine. In either case, if the mix control plug is not being used, and is NOT part of a CCC system (so no ECM controlled timing) your best bet is to simply replace it with a Q-jet that has no electrical controls. (again, short of the choke) I know the trucks had electric chokes by 1983, so anywhere around that vintage would likely be a good donor.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Re-reading some of the other posts you made, sounds like you've got a gas smell from the exhaust. More than likely it is something to do with the carb, so if you don't have the plug, there really isn't any reason to rebuild it, it would be better to get another one to rebuild than to rebuild one that is never going to work as intended.
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    Just pulled my C/K parts manual out (85/86), figured I'd put this out here, since there seems to be some misunderstanding of what these trucks got for carbs.

    The trucks could have had:

    E4ME True CCC (meaning with an ECM) carb, TPS and Mix Control

    E4MED True CCC, TPS and Mix control, WITH a dual capacity pump. Not sure what it does, but the dual capacity valve sits underneath the mix solenoid. This one has ANOTHER wiring connector coming off of of the MC solenoid connector. The dual capacity pump I'm thinking somehow cuts fuel to something under certain conditions based on temperature, but its not possible to tell from the parts diagram.

    M4ME "standard" Quadrajet, no electrical connectors except electric choke.

    M4MED This is one of the carbs that *looks* like its CCC, but is not. The "mix control" is ONLY a dual capacity pump, although it is identical when seen on the carb, as a real mix control. there is no TPS on the drivers side front.

    M4MEF Another "standard" Q-jet. Only major difference I see between this and the M4ME is that this carb has an aneroid cavity plug. (thats where the mix control would sit in another application)

    M4MC This is another "standard" carb, but it visually looks like a Buick, Olds or Pontiac Q-jet, with the "straight in" fuel filter housing. This is a 454 application if I remember correctly, based on the filter orientation.

    1982 ONLY could have an M4MC or M4ME carb, neither of which had a dual capacity pump or ECM controls of any type.

    Just thought I'd throw these out there, may help someone on their rebuild trying to look up float specs.
     
  15. R72K5

    R72K5 Banned

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    if you are referring to ECM being the EST system then 81 and 82 also had E4ME type carb since 81 was the first year of the EST system.


    what you think ?
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    No, the ECM is used *ONLY* in conjunction with a TPS and O2 sensor. I know for a fact my '82 service manual doesn't list any ECM applications.

    EST was distributor/knock sensor only, and although it has an "ECM", and sits in the EXACT same place as an 87-91 TBI truck (and I'm sure CCC trucks) it only does the above jobs. It has nothing to do with carb operation.
     

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