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Thread: Unsure of dwell reading

  1. #1
    absotively posilutely bytes311's Avatar
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    Unsure of dwell reading

    I just purchased a dwell meter and I'm trying to adjust my fuel mixture because it been tampered with in the past, however, I'm not exactly sure how to read it. I heard that it should fluctuate between ~30 and ~50 when the O2 sensor kicks in, but I just watched a YouTube video of someone adjusting their dwell with the same (or similar) meter, and his fluctuated around 20 and 30 on the bottom, 6 cyl scale. so now I'm not sure where mine is supposed to be.

    Here is his video: https://youtu.be/MbE-2k4Cy4E

    The first pic is where the needle sits before the O2 sensor kicks in. The second pic is what happens when I press on the full throttle switch.
    20150525_114148.jpg

    20150525_114205.jpg

    Edit: Here is my dwell reading: http://youtu.be/FTUJCUIWFhg
    Last edited by bytes311; 05-25-2015 at 03:19 PM.

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    The book numbers use a 4 cylinder scale. So you read the 8 cylinder and double it with your meter. They used 4 cylinder to get more accuracy with the readout on meters that have selectable scales. They are really reading duty cycle but the dwell meter was a common mechanics tool that reads duty cycle on a different scale.

    Duty cycle is a 0 to 100 % scale.

    Dwell for 4 cylinder is 0 to 90 degrees.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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    Quote Originally Posted by Bitsyncmaster View Post
    The book numbers use a 4 cylinder scale. So you read the 8 cylinder and double it with your meter. They used 4 cylinder to get more accuracy with the readout on meters that have selectable scales. They are really reading duty cycle but the dwell meter was a common mechanics tool that reads duty cycle on a different scale.

    Duty cycle is a 0 to 100 % scale.

    Dwell for 4 cylinder is 0 to 90 degrees.
    Refer to D:04: 14-15. To verify you are getting correct readings set the WOT micro and you should read 50-60 steady (or 1/2 of that if you are reading on an 8 cylinder scale). That will tell you the Lambda ECU is at least getting power and you are able to get readings out of it. You may still have a contaminated O2 sensor. There are other checks to test the Lambda ECU without the O2 sensor. Adjusting the mixture is the LAST thing you do. You have to make sure everything else is perfect first. That includes spark plugs, ignition wires, vacuum leaks, valve adjustments, injectors, etc.
    David Teitelbaum

  4. #4
    Senior Member Jonathan's Avatar
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    Quote Originally Posted by bytes311 View Post
    I just purchased a dwell meter and I'm trying to adjust my fuel mixture because it been tampered with in the past, however, I'm not exactly sure how to read it. I heard that it should fluctuate between ~30 and ~50 when the O2 sensor kicks in, but I just watched a YouTube video of someone adjusting their dwell with the same (or similar) meter, and his fluctuated around 20 and 30 on the bottom, 6 cyl scale. so now I'm not sure where mine is supposed to be.

    Here is his video: https://youtu.be/MbE-2k4Cy4E

    The first pic is where the needle sits before the O2 sensor kicks in. The second pic is what happens when I press on the full throttle switch.
    20150525_114148.jpg

    20150525_114205.jpg

    Edit: Here is my dwell reading: http://youtu.be/FTUJCUIWFhg
    How did this end up for you Daniel? What adjustments, if any, did you make? Mine is doing something similar to what you showed in your video.
    One damn minute Admiral...


  5. #5
    absotively posilutely bytes311's Avatar
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    Hi Jonathan,

    In my case, I installed new spark plugs and a new o2 sensor. I haven't had any issues with my dwell since.

  6. #6
    Admins Never Retire Ron's Avatar
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    Quote Originally Posted by Jonathan View Post
    Mine is doing something similar...
    If yours pulses, centered about the 20 mark, on the 8 cyl scale, it's good to go.

  7. #7
    Senior Member Jonathan's Avatar
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    Quote Originally Posted by Ron View Post
    If yours pulses, centered about the 20 mark, on the 8 cyl scale, it's good to go.
    At times it has, but not so much now. Let me summarize recent observations.

    I have the Actron dwell meter. Also have a 3 mm t-handled hex wrench and my tamper proof cap was already removed when I got my car and the DMCH rubber plug has been in the hole ever since.

    Most recently, including today, the car would idle immediately after starting from cold and the dwell would hold steady in that 50-60 range.

    (The dwell numbers I am referencing are what is read off the 8 cyl scale and then multiplied by 2).

    This would be the case for around one minute or two and then it would seem to hold steady at 44. It would keep holding steady at 44 for the majority of the time, even after I had warmed the car up enough idling to kick the cooling fans on and off.

    At times, either by chance or the coincidence of revving the car up, it would pulsate instead of staying at that steady 44. The pulsation though is much higher than centering around 40 (what you meant by 20 deg, Ron) and it would be up to 75 and then down to 44 or so. It doesn't do this terribly consistently, as it seems to at times blip when going down to 44 and then want to pulsate around the 40 like I would want to see it do, but it will then either go back to the high and wide range pulsating or just hold steady at 44.

    Early dwell measurements and other observations were pointing to my car being set rich, so I intended on leaning it out slightly. Upon removing the rubber plug, I could hear a distinct change in engine performance (affect from the vacuum leak?). I did make a small adjustment to the mixture screw, and would consider it "two hours" counterclockwise, in the sense that when I secured the 3 mm hex wrench, the handle was aimed at 10 pm and I went down to 8 pm (understandable?). I could put it back as it was easily if need be.

    I did also notice that when you secure the wrench in the hole, you can push down the lever arm assembly that it is all connected to fairly easily and have the engine change pitch or sputter or whatever. I would assume that's to be expected after looking at the system diagram in the workshop manual and seeing what is going on under there.

    The workshop manual diagnostic chart when seeing this steady at 40-50 mark, indicates the oxygen sensor is disconnected. I do not think mine is physically disconnected, not what is visible on the wire or connector anyway. I would think this is telling me the sensor is fouled or faulty one way or the other, yes?

    I do have a replacement oxygen sensor I can put in but have not yet done so. I reread David saying everything else needs to be perfect, so assume a new and/or reliable oxygen sensor has to be in place before you can move on confidently to that final step of adjusting the CO mixture?

    Consensus is to replace oxygen sensor as next step? yes/no?
    One damn minute Admiral...


  8. #8
    Senior Member Chris 16409's Avatar
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    I was having similar issues and I replaced the Oxygen sensor, and it seems to have fixed the staying in open loop behavior. However, I also replaced one of the wires that bolts to the passenger side of the intake manifold that originates at one of the valley sensors. That could have been causing issues too.
    Chris Miles

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    1983 Grey Manual, VIN #16409, Fresno, California

  9. #9
    Admins Never Retire Ron's Avatar
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    Quote Originally Posted by Jonathan View Post
    At times it has, but not so much now. Let me summarize recent observations.

    I have the Actron dwell meter. Also have a 3 mm t-handled hex wrench and my tamper proof cap was already removed when I got my car and the DMCH rubber plug has been in the hole ever since.

    Most recently, including today, the car would idle immediately after starting from cold and the dwell would hold steady in that 50-60 range.

    (The dwell numbers I am referencing are what is read off the 8 cyl scale and then multiplied by 2).
    Same as mine. All Good here.

    Quote Originally Posted by Jonathan View Post
    This would be the case for around one minute or two and then it would seem to hold steady at 44. It would keep holding steady at 44 for the majority of the time, even after I had warmed the car up enough idling to kick the cooling fans on and off.
    I think it should have kicked in well before the fans kick in (59F according to the manual). I know I am too picky (Dave S tells me I worry about a lot of exact specks too much when I call and bug him sometimes, which I have found to be case), but I try to get them dead on anyway LOL...But I think this IS too far off. I'd confirm and suspect the temp sensor. But, that be the case, it is only late to switch and wouldn't change readings afterwards...

    Quote Originally Posted by Jonath
    an;181288
    At times, either by chance or the coincidence of revving the car up, it would pulsate instead of staying at that steady 44. The pulsation though is much higher than centering around 40 (what you meant by 20 deg, Ron) and it would be up to 75 and then down to 44 or so. It doesn't do this terribly consistently, as it seems to at times blip when going down to 44 and then want to pulsate around the 40 like I would want to see it do, but it will then either go back to the high and wide range pulsating or just hold steady at 44.

    Early dwell measurements and other observations were pointing to my car being set rich, so I intended on leaning it out slightly. Upon removing the rubber plug, I could hear a distinct change in engine performance (affect from the vacuum leak?).
    I did make a small adjustment to the mixture screw, and would consider it "two hours" counterclockwise, in the sense that when I secured the 3 mm hex wrench, the handle was aimed at 10 pm and I went down to 8 pm (understandable?). I could put it back as it was easily if need be.
    When I get one to where you describe above, it is usually a tad rich. "Two hours" is A LOT. Try moving it a little as possible CCW, in steps... It is touchy especially when you get it close. ...Drag it lean (say, swinging @ 35) on purpose so you will know the range.
    Note any time it is warm, idling, and it just sets there, you might have it so far off that it can't compensate.*
    (I should mention I have see some I could not get to sit like this tho).

    Yes, it's a vacuum leak. Always plug the hole with your finger, rev the engine once to clear it out and wait a bit for it to settle down, and then take a reading!

    Quote Originally Posted by Jonathan View Post
    I did also notice that when you secure the wrench in the hole, you can push down the lever arm assembly that it is all connected to fairly easily and have the engine change pitch or sputter or whatever. I would assume that's to be expected after looking at the system diagram in the workshop manual and seeing what is going on under there.
    Yep, normal.

    Quote Originally Posted by Jonathan View Post
    The workshop manual diagnostic chart when seeing this steady at 40-50 mark, indicates the oxygen sensor is disconnected. I do not think mine is physically disconnected, not what is visible on the wire or connector anyway. I would think this is telling me the sensor is fouled or faulty one way or the other, yes?
    Make sense. (As long as you don't have it WAY off as with * above).

    Quote Originally Posted by Jonathan View Post
    I do have a replacement oxygen sensor I can put in but have not yet done so. I reread David saying everything else needs to be perfect, so assume a new and/or reliable oxygen sensor has to be in place before you can move on confidently to that final step of adjusting the CO mixture?
    Absolutely.

    Quote Originally Posted by Jonathan View Post
    Consensus is to replace oxygen sensor as next step? yes/no?
    Yes (If not as with * above.)

    Did you do ALL of the tests in D:04:15?
    Last edited by Ron; 10-01-2015 at 08:18 PM.

  10. #10
    Senior Member Bitsyncmaster's Avatar
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    I have seen a couple cars have dwell reading problems when the CAT is plugged. What I remember is you make the adjustment and it never seems to hold the dwell reading and swings way off again after it runs a little while.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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