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Thread: Attempting to destroy my idle lumpiness

  1. #21
    Senior Member
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    Quote Originally Posted by NckT View Post

    Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

    Good luck

    NickT
    Nick, Coming to Houston anytime soon? I'm sure we can put your expertise to good use!
    Shannon

  2. #22
    Member NckT's Avatar
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    Location:  Yorkshire UK

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    Quote Originally Posted by lazabby View Post
    Nick, Coming to Houston anytime soon? I'm sure we can put your expertise to good use!
    I've never visited America before, it'll be worth a visit at some point.
    RIP Rob van de Veer Top bloke

    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

  3. #23
    Member NckT's Avatar
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    Quote Originally Posted by NckT View Post
    There are 2 independent systems, and both considered as fixed independent feedback PID control systems with 2 separate Process Variables (PV), fixed Setpoints (SP) fixed Proportional Integral, Derivative values contained within the circuit design.

    However, looking at the system with my "Control Engineer" head on, the two Output (OP) are the frequency valve and the Idle control valve.

    The main influence of the idle oscillation, other than the odd fire design is the output variable of the idle speed control valve with range 0 to 100% of the valve being 0 to 775 rpm. This control of the Output OP of the Isle control can be influenced such that the output control changed to 725rpm to 775 so full scale deflection of the valve adjusts this small idle range.

    This is how I do it, applying experience and experimentation on my own D noting feedback values using oscilloscope to evaluate the feedback etc:

    Gently screw all of the 3 brass screws down.
    Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each.
    Note the current average idle speed.
    Unscrew the brass screw with the slot open until the idle speed is.higher than the previous reading, at this point screw it back in by half a turn.
    Re check that the dwell of the idle computer is between 35 to 45 degrees. My preference is that the max.swing of the dwell is about 44
    Turn engine off
    Fit a metric feeler gauge with "30" in between the lower throttle body screw and its stop.
    Adjust the top throttle stop so it just closes the microswitch. This adjustment is important to stop the timing of the idle valve from operating too soon or too late that can cause an off idle oscillation to critically dampen the idle response.

    In effect, this adds an air bypass around the throttle plate and the opening of the 2 brass screws by a fixed amount adds the bypass as an air damped effect to critically damped the air flow, effectively changing the Integral of the control to critically dampen the oscillation.

    The above assumes everything else is tested and working and that the control pressure and primary fuel pressure is correct and calibrated and that the oxygen sensor oscillates at least by approx 5 hertz at 3000 rpm. It'll also assume that the closing of the throttle is repeatable closed with no mechanical sloppiness.

    Although not to "book" it makes the engine run right. I've done this procedure on 40 plus Deloreans at Tech events with oem config catalysed exhausts to performance exhausts with standard k jet to imported (to UK) "Stage 2" (ex Steve Wynnes car I believe) with the performance cams etc with repeatable results.

    Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

    Good luck

    NickT
    I do apologise about the spelling errors, I'm typing this on my "smart" phone.

    In addition, the following:

    "Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each."

    Should be:

    "Unscrew the 2 brass screws nearest the inlet manifold W pipe by 2 full turns each."

    Next time I'll use a PC.

    Sorry all.

    NickT
    RIP Rob van de Veer Top bloke

    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

  4. #24
    Junior Member
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    Location:  IRELAND

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    My VIN:    6100,0707

    Just another angle on the lumpy idle.. Back in the mid to late 80's ( i know, before a lot of you guys were born ) Mercedes Benz's had the same problem with there cars using the same fuel system at the "D's" mainly there big v8's .. A cure they found was to up grade the steel injector with a brass one.. Lumpy idle cured .. Just a thought.

  5. #25
    Delorean Guru
    Join Date:  May 2011

    Location:  Northern NJ

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    Club(s):   (DMA)

    I have experimented with increasing the air bypass similar to what you have described and noticed the idle was smoother. My take is that by reducing the amount of control of the idle motor, the motor was able to dampen itself. I agree, setting things up "by the book" will not give the smoothest idle if that is your goal. I did not do emissions testing but I suspect doing it by the book is the better way for emissions and that is why it is the method offered in the book. The "best" way IMHO is to go ahead and get the motor running the best you can "by the book" and if you then want a smoother idle adjust the air bypass to smooth it out. The only problem I see in your method is that on many cars the heads are broken off of 1 or more of the brass screws. BTW, you are confirming that a "properly set up" PRV "by the book" doesn't run smoothly. I agree, I also agree your method will make it run smoother.
    David Teitelbaum

  6. #26
    Not a DeLorean Guru
    Join Date:  May 2011

    Location:  Rochester, NY

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    An in-tune and properly running PRV will run just fine. Put down the books and start actually working with cars, Dave.
    -Mike
    1981 DeLorean, heads/cams/exhaust, EFI
    1999 Corvette, heads/cam/exhaust, 440 BHP
    2005 Elise, stock
    2016 Chevy Cruze

  7. #27
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    Quote Originally Posted by opethmike View Post
    An in-tune and properly running PRV will run just fine. Put down the books and start actually working with cars, Dave.
    I don't now where you came up with the idea I don't work on cars?
    David Teitelbaum

  8. #28
    Senior Member Trstno1's Avatar
    Join Date:  Aug 2014

    Location:  Anchorage, Alaska

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    Quote Originally Posted by NckT View Post
    There are 2 independent systems, and both considered as fixed independent feedback PID control systems with 2 separate Process Variables (PV), fixed Setpoints (SP) fixed Proportional Integral, Derivative values contained within the circuit design.

    However, looking at the system with my "Control Engineer" head on, the two Output (OP) are the frequency valve and the Idle control valve.

    The main influence of the idle oscillation, other than the odd fire design is the output variable of the idle speed control valve with range 0 to 100% of the valve being 0 to 775 rpm. This control of the Output OP of the Isle control can be influenced such that the output control changed to 725rpm to 775 so full scale deflection of the valve adjusts this small idle range.

    This is how I do it, applying experience and experimentation on my own D noting feedback values using oscilloscope to evaluate the feedback etc:

    Gently screw all of the 3 brass screws down.
    Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each.
    Note the current average idle speed.
    Unscrew the brass screw with the slot open until the idle speed is.higher than the previous reading, at this point screw it back in by half a turn.
    Re check that the dwell of the idle computer is between 35 to 45 degrees. My preference is that the max.swing of the dwell is about 44
    Turn engine off
    Fit a metric feeler gauge with "30" in between the lower throttle body screw and its stop.
    Adjust the top throttle stop so it just closes the microswitch. This adjustment is important to stop the timing of the idle valve from operating too soon or too late that can cause an off idle oscillation to critically dampen the idle response.

    In effect, this adds an air bypass around the throttle plate and the opening of the 2 brass screws by a fixed amount adds the bypass as an air damped effect to critically damped the air flow, effectively changing the Integral of the control to critically dampen the oscillation.

    The above assumes everything else is tested and working and that the control pressure and primary fuel pressure is correct and calibrated and that the oxygen sensor oscillates at least by approx 5 hertz at 3000 rpm. It'll also assume that the closing of the throttle is repeatable closed with no mechanical sloppiness.

    Although not to "book" it makes the engine run right. I've done this procedure on 40 plus Deloreans at Tech events with oem config catalysed exhausts to performance exhausts with standard k jet to imported (to UK) "Stage 2" (ex Steve Wynnes car I believe) with the performance cams etc with repeatable results.

    Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

    Good luck

    NickT
    Holy Cow! I just did the adjustments you suggested and my engine is now running better than it has the whole time I've owned it. Kudos sir!! Now, ill let it cool off and see what the adjustments do to my initial cold start up. But when warm holy cow it runs smooth and my engine vibration is 98% gone!

    You the man!

    Thank you for replying to the thread!!!
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

  9. #29
    Member NckT's Avatar
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    You're welcome. I just hope you noted my post 6 posts earlier about my amendment.

    I'm glad it worked out for you.

    NickT
    RIP Rob van de Veer Top bloke

    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

  10. #30
    Member
    Join Date:  May 2011

    Location:  Surrey, United Kingdom

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    Just to add my 2pence worth, Nick very kindly setup my car using this method a number of years ago and it totally transformed it.

    My car hunted a lot, as can be seen in this cold start video I took back in 2012, it was all over the place.
    https://youtu.be/oXy4y5Cpa0s

    Fast forward to 2013 and here is a video of a cold start after Nicks adjustments, the results speak for themselves.
    https://youtu.be/Glh_TaTSP1A

    Having seen Nick perform this on multiple other cars over the years, I can say that this method consistently gives repeatable results. Idle is smooth across all engine temps, cold/warm/hot, it always runs smooth. Heed his advice on this setup, ignore the "book".


    Quote Originally Posted by David T View Post
    I did not do emissions testing but I suspect doing it by the book is the better way for emissions and that is why it is the method offered in the book.
    My emissions results were better after Nicks adjustments - In the UK emissions are tested yearly as part of the annual vehicle (MOT) test.
    Last edited by MikeWard; 09-07-2017 at 03:42 AM.
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