Rebuilt CCC Qjet Tuning

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

  1. RickM

    RickM Veteran Member

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    The TPS is just a variable resistor, just put an ohm meter on it and see if it changes resistance smoothly, if so it is OK.

    Have you drilled out the plug that lets you adjust the TPS?

    Sorry if I missed a previous post saying that you did.

    Getting that plug out can be tough, ask me, I ruined a couple of carbs until I learned how to get the plug out.

    Also, are you sure you have 2/32 - 4/32 travel of the mixture control solenoid?

    If you are not in that range you will never get the varying dwell.

    Even if you have the correct MCS solenoid travel, if the lean stop and rich stop initial settings are off you will never obtain the varying dwell. Refer to the service manuals on how to set them.

    If you feel they are correct then adjust them, (I cant remember which one, lean or rich stop, to adjust when the dwell is low, remember to adjust either both up or both down, also remember the lean stop is fine thread so you will need to turn it twice as much as the rich stop), with the car running until you get the varying dwell.

    It is not hard once you understand how it works.

    Hope this helps
    RickM

    RickM
     
    Last edited: Aug 20, 2020
  2. MP81

    MP81 Veteran Member

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    Let me try and summarize:

    Haven't ohm'd the TPS, but without the accelerator pump arm, it reads like 4.6V on the OTC Monitor 2000 - my understanding is the adjusting screw changes its "starting" position in the "barrel" in the main body of the carb, relative to the accel pump arm. With no arm, it should be the lowest possible voltage.

    The plug was already drilled out (thankfully), so I purchased a 2.5mm hex nutdriver to adjust it. Adjusting it didn't really do much to the voltage, since the TPS is reading so high with the plunger fully extended.

    In the past I confirmed that the MCS travel is within that spec, yes.

    With the OTC Monitor 2000, I was able to confirm that my buddy's Innova timing light (with dwell reading) was reading correctly at 3* of dwell, and confirmed the car is indeed in closed loop, but reading rich. If I gave it a punch of throttle (while idling), it'll switch to lean for a second, dwell drops to 2* (indicating more fuel going in to correct), then goes back to 3* when it goes back to reading rich.

    The theory is: the TPS sensor is reading near-WOT levels with the throttle sitting against the idle stop, so it's adding extra fuel, causing the dwell to "read" stupidly rich. I can't really adjust the rich or lean stops until I get the TPS adjusted to the correct voltage at curb idle - but it doesn't seem like this one is willing to do that.
     
  3. MP81

    MP81 Veteran Member

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    I bought a new NTK TPS and figured I would test it out, outside of the carb, just to make sure it didn't read crazy high as well.

    With the plunger completely out, it read 0V, and with it all the way in, about 5V - looks like I have confirmed that the original TPS is bad. Now I just need to remove the air horn and swap em.
     
  4. MP81

    MP81 Veteran Member

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    Got the new TPS installed today - after a few cycles of adjusting the TPS voltage, curb idle speed, TPS voltage again and then the idle air bleed, we're in business.

    I turned the idle air bleed in probably two and a half full turns, so that's the majority of why the dwell was reading so damn rich at 3 degrees. Got it varying between 28 and 32 degrees now. TPS at 0.56V and idle at 700 RPM.

    Once I get my door seals in and my door panels back on (because the armrests and hardware are in each footwell), I'll get the thing out on the road and see how it does.
     
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  5. MP81

    MP81 Veteran Member

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    Dumb question (can't seem to find an answer in the service manual, though): curb idle is adjusted when the engine is up to operating temp, yes?

    Long story short: I brought the car out on Wednesday for the first drive in a year...but it was idling like poo, and I basically had to redo all the "calibration" again. I drove it twice yesterday (once to go get gas, and then a much longer drive down to Woodward for probably the last "car night" of the year...at least in the Camaro, since it doesn't have working heat) and it was not thrilled on a cold start. Overall, it ran like poo, most of the time.

    I realized that all these times, the car never went into high idle. I just adjusted the choke (which I had set before just fine, so I'm not sure why it was an issue...maybe the ambient temp when I set it last time was a problem? It's been high 70s the last few days, but I'd still think it should start with a closed choke, high idle and eventually do its thing?) so that the plate is barely open, and thus the linkage there will allow the engine to idle high, instead of it idling at like...400 rpm and trying to die. You have to give it a fair bit of gas, and it sounds like it's sputtering/breaking up (almost like someone's voice cracking as they go through puberty...that's the best - and most awkward - way I can describe it) to keep it running. I think the initial idle issue was just the choke being wide open too early.

    But the rest of the stuff...this should be a "set it and forget it" type of deal...not constantly have to recalibrate the vehicle any time I drive it. It's not like anything can really move, either.

    So I guess one step at a time now...
     
  6. MP81

    MP81 Veteran Member

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    So I messed with it more on Tuesday. The choke working helped a lot, but I still had to adjust everything again. Once I got it "dialed in" again, it did seem to run pretty good out on the road. No idea if that will "hold" or not...

    Which brings me to the next thing - since I can see whether or not it's in closed loop, I noticed that as the car warmed up, and I was making my adjustments, sometimes if it fell back into open loop (since it's just idling, with me occasionally giving it a few seconds of throttle to keep it in closed loop), the idle speed would start to drop down to like...500 rpm, trying to die. Giving it gas would usually result in a brief hesitation, then revving up like intended. Once it was back in closed loop, no issue at all. Is this pointing to something else?

    I should set this all once and be good to go, in my mind, not spend 20 minutes tuning the carb any time I want to drive the car. I went to move the car out of the center of the garage the next day (so I could pull my Cobalt back in, as it was done at the dealer - why would I pull the fuel tank to replace the fuel pump if they'd do it for free, and replace the tank for free at the same time?) and it took a lot of cranking, presumably the float bowls were already empty? I do have none of the tamper-proof plugs in, so there's a few...extra...vent holes - does it evaporate that quick? Or, could the fuel pump be problematic and not be filling the float bowls up quick enough causing issues?

    Thoughts?
     

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