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Thread: Engine Hunts at Start and Then Rough Idle When Warm

  1. #21
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    Quote Originally Posted by opethmike View Post
    Is it set to 4 cylinder mode?
    Yes.

    https://youtu.be/8Ca4UV654cE
    Last edited by lazabby; 07-15-2017 at 10:33 AM.
    Shannon

  2. #22
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    Quote Originally Posted by Jonathan View Post
    Hey Shannon, when I was doing some dwell meter/mixture setting troubleshooting and fine tuning, it did the same thing where it stayed at one reading instead of fluctuating and also tended to settle in after running for a few minutes. In my case, it turned out to be a bad O2 sensor.

    I didn't manage to get my own O2 sensor out and replaced, so I took it to a shop I've used in the past and he got it out, replaced it and then set the dwell properly. Idle and fuel mileage has been good ever since.

    I'm sure there is a more technical or scientific explanation as to what happens with that circuit when the O2 sensor fails to cause it to stay steady or not fluctuate or whatever. I don't have that explanation, but also figured I didn't need it after a new O2 sensor in my car fixed it all up anyway.

    I couldn't get your youtube video to play by the way. It was marked as private.
    Jonathan thanks. That's what I'm suspecting. I'll probably replace it.

    Thanks for letting me know the setting on the video. Didn't know it was marked private.
    Shannon

  3. #23
    Senior Member Jonathan's Avatar
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    You can also double check the O2 sensor reference ground wire is still connected properly. It is the one which grounds to the block under the air filter housing, pretty much in the far corner passenger side and towards the front of the car. You can identify it fairly easily because a couple inches of the ground wire has a red wrap on it. The wire is only six inches or so long and the free end has a black quick connector (very similar to the ones used on the ballast resistor connections). The other end of that wire ultimately connects with the ECU behind the driver's seat. It could be another wiring connection that's not making good contact or not connected at all perhaps. And easy enough to check.

    O2 sensor ground.jpg

    My photo is slightly misleading as I had to relocate mine since the hole it's meant to go into had a broken off screw in it. The red arrow points to the hole your red ground wire is probably screwed into.
    One damn minute Admiral...


  4. #24
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    Quote Originally Posted by Jonathan View Post
    You can also double check the O2 sensor reference ground wire is still connected properly. It is the one which grounds to the block under the air filter housing, pretty much in the far corner passenger side and towards the front of the car. You can identify it fairly easily because a couple inches of the ground wire has a red wrap on it. The wire is only six inches or so long and the free end has a black quick connector (very similar to the ones used on the ballast resistor connections). The other end of that wire ultimately connects with the ECU behind the driver's seat. It could be another wiring connection that's not making good contact or not connected at all perhaps. And easy enough to check.

    O2 sensor ground.jpg

    My photo is slightly misleading as I had to relocate mine since the hole it's meant to go into had a broken off screw in it. The red arrow points to the hole your red ground wire is probably screwed into.
    The ground is there. I replaced the O2 sensor but I'm still getting a reading between 10.5 and 11 on the dwell meter at 4 cylinder. You can see it on the video. What's going on? The car still hunts a little when starting but smooths out when warm.
    Shannon

  5. #25
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    Quote Originally Posted by lazabby View Post
    The ground is there. I replaced the O2 sensor but I'm still getting a reading between 10.5 and 11 on the dwell meter at 4 cylinder. You can see it on the video. What's going on? The car still hunts a little when starting but smooths out when warm.
    What do you get with the sensor unplugged?
    -Mike
    1981 DeLorean, heads/cams/exhaust, EFI
    1999 Corvette, heads/cam/exhaust, 440 BHP
    2005 Elise, stock
    2016 Chevy Cruze

  6. #26
    Senior Member Jonathan's Avatar
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    Quote Originally Posted by opethmike View Post
    What do you get with the sensor unplugged?
    Mike's thinking the same thing I was... to confirm what you get for each of the troubleshooting steps:

    Dwell troubleshooting.jpg
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  7. #27
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    Quote Originally Posted by Jonathan View Post
    Mike's thinking the same thing I was... to confirm what you get for each of the troubleshooting steps:

    Dwell troubleshooting.jpg
    I'll try it with the sensor unplugged. Might take a day or two to get back with a response.
    Shannon

  8. #28
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by opethmike View Post
    What do you get with the sensor unplugged?
    That number is saying your mixture is pretty far off. The ECU has maxed out it's adjustment range. Move your mixture screw a little bit one way or the other and see if that number changes.
    Dave M vin 03572
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  9. #29
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    Quote Originally Posted by Bitsyncmaster View Post
    That number is saying your mixture is pretty far off. The ECU has maxed out it's adjustment range. Move your mixture screw a little bit one way or the other and see if that number changes.
    I am thinking the same thing.

    Shannon, any chance you can get a hold of a wideband O2? That could aid quite a bit.
    -Mike
    1981 DeLorean, heads/cams/exhaust, EFI
    1999 Corvette, heads/cam/exhaust, 440 BHP
    2005 Elise, stock
    2016 Chevy Cruze

  10. #30
    Senior Member DMCFL Brandon's Avatar
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    Lean it out a bit and see if it changes.
    Brandon S.

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    2016 Toyota Tacoma SR5 V6


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