Rebuilt CCC Qjet Tuning

Discussion in 'Engine Topic' started by MP81, Oct 8, 2019.

  1. MP81

    MP81 Veteran Member

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    How did you know the coolant sensor had gone bad? Was the car throwing a code?

    So, if I short the two pins on the diagnostic connector to read any codes, I can hear them rapid-firing from under the hood. If I just key on, they're not going. Not sure if they're supposed to be moving when I'm just in key-on, or only when the car is running (when you'd not really be able to hear them anyway).

    Distributor is original, so that should be good. O2 is old, but I have a new engine-side pigtail so I can go ahead and get a true extension harness and install the new O2 I have for the car.
     
  2. ale81

    ale81 New Member

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    Actually, my temp sensor had not gone bad but given the state of the wiring and that this is my daily driver, I wanted to know that it would be reliable so I did the replacement.

    I don’t think the MCS is supposed to fire with just the key on (except when shorting the diagnostic connector). Mine doesn't and I think I recall a post by member Damon that some cars did but not the Camaros. I don't know if mine is louder than normal but you can definitely hear it clicking with the engine running. Maybe try unplugging and plugging yours back in while it's running? There should be some sound difference. Or maybe stick a test light on it to see if you get a strobe effect.
     
    Last edited: Nov 11, 2019
  3. MP81

    MP81 Veteran Member

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    I'll have to put my ear there sometime. You definitely hear them going crazy with the diagnostic port shorted, so I imagine they'll work during regular operation too.

    Given that it has decided it is now January in November, I don't expect I'll be getting around to it too soon - but once it warms back up into the 40s where it should be, I'll try to go have a listen.

    Given that the wiring is pretty clearly an issue on the coolant sensor, I'm thinking I'll do what you did - put the kind I posted earlier on with the newer-style pigtail (which looks better anyway). I'm thinking I might tee it to work for both that coolant sensor as well as my Dakota Digital sensor that I currently have in the thermostat housing (so I can have a coolant reading at times other than when the thermostat opens).
     
  4. MP81

    MP81 Veteran Member

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    So I wanted to update this a bit - I finally got around to putting my new O2 sensor in the car, along with modifying the extension harness to be a true separate harness - previously I just extended the old O2's wiring, as I didn't want to cut up my new O2 harness. I bought a new engine-side O2 pigtail and replaced the old O2 sensor and now have a harness with plugs at both ends - like those more readily available for newer vehicles.

    Anyway, once I got the car started (the choke was sticking open, as the car hasn't been started since the beginning of October, so I had to kind of work that back to being closed), it sat there and idled at 700 rpm, without moving, for 20 minutes. No up and down like it used to. No "switch-flip" to a sudden super-high idle...700. Rev it and they come back down to 700.

    So, it's very likely my old O2 was reading lean, and that "switch-flip" was the car going into closed-loop, thinking the engine needs more fuel and thus adding it in, causing the RPMs to increase and revs to hang.

    Still couldn't get any kind of dwell reading off the wire, aside from "3", but the car seems to be running properly...
     
  5. 1980RS

    1980RS Veteran Member

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    As I remember from back then there was a green pig tail that we used to check the dwell. I always used the GM Tech 1, made the job easier. I think I have a complete q-jet all stock non modified sitting in the basement, was off a HO 305 z car. Man I worked on a ton of those CCC carbs back in the day.
     
  6. MP81

    MP81 Veteran Member

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    Yup - that's the connector - I'm using a timing light that also measures dwell, but the car never seems to get into varying dwell - it just always reads "3".
     
  7. 1980RS

    1980RS Veteran Member

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    Might be stuck in open loop.
     
  8. MP81

    MP81 Veteran Member

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    I'm not sure if it is or not - changing the O2 made a massive change to how the vehicle runs, especially at the point where, like a switch, RPM would suddenly jump up to like 1500-2000 RPM and revs would hang. Replacing the O2 made that stop happening. You could still tell when that "switch" flipped, and RPM jumped ever so slightly, but went right back down to 700 and stayed there. My thinking is, if it was stuck in open loop, the O2 sensor should have had no impact on how the engine runs, since it's not in use.
     
  9. RickM

    RickM Veteran Member

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    If the dwell meter is not varying, then something is wrong. Do you have the meter set on the 6 cylinder setting?
    Also, this easy test will tell you if you if the computer is in closed loop and if the O2 sensor is working.

    First, put your hand over the carb or manually partially close the choke creating a rich condition if the meter moves then you know the computer thinks the engine was running lean and was asking to enrich the fuel mixture. If nothing happens pull off a vacuum hose like the pvc valve and create a lean condition if the meter moves then computer thinks the engine is running to rich and was asking to lean the fuel mixture.

    Your job is to figure out why the car is running lean or rich.

    If the meter does not move at all then the computer is not in closed loop mode and you need to figure out why.

    Hope this helps
    RickM
     
  10. MP81

    MP81 Veteran Member

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    Yup, I have it set to the 6-cylinder setting. Now, all of this is being done with the car stationary in my garage - can't drive it around, as it's still on storage insurance. I do rev it a good bit and try to play around with the rpm range to throw in some engine speed variance, but it's not like that you get with driving. Do I need to actually go out there and drive it to get it into varying dwell, or should it do it sitting in the garage?

    I could do a burnout in my driveway, but my neighbors (and wife) might be upset, haha.
     

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