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Thread: follow on for troubleshooting assistance

  1. #1
    Junior Member
    Join Date:  Nov 2017

    Posts:    20

    follow on for troubleshooting assistance

    Started a thread about a year ago trying to help a work friend out with an acquired delorean by another friend with some issues. Working on it has been hit or miss although we are back at it after the owner finally got some of the parts we knew were issues. I feel we have learned much and although a former auto tech I had never messed with the types of systems on this car. With that said, I wanted to get a fresh start with some questions. The older post can be visited here:

    http://dmctalk.org/showthread.php?16...I-need-help-on

    Anyways, after several repairs to try and get the car back to somewhat in working order we have confirmed the following:
    -CSV system is operating normally after repairs
    -ICS is operating although I question why we are only seeing 650 rpms as I understood it should be around 750. Before this was running much higher and we found the mechanical rigging off. Also had a bad thermistor.
    -Repaired several vacuum leaks. (I didn't even think about checking injectors for air leaks and that will be next)
    -Adjusted valves
    -Repaired the warm up circuit melted wires controlling the fuel pressure.

    Where we are at is last night we checked/set timing to 13 degrees. It was at about 16 degrees. Now it is quite boggy and backfires/gurgles with a quick throttle hit. We went off the number one cylinder (back cylinder RH side of car) and used the what I would call more of the middle mark. I read somewhere that this mark would be if taking spark from the #6 cylinder although I question if this is accurate and against anything I had done in the past. The car still appears to be very rich when cold due to the fumes being created from the exhaust. We also double checked the idle air mixture setting with a dwell meter. I question if we are having an issue here as any changes to the mixture screw did not make much of a difference in dwell reading of around 30. (see attached) Every now and then you would get a bit of fluctuation. I could have sworn that when we checked this previously we could get more significant changes and the reading was much higher.

    I question if one of the things we should check is fuel pressure difference of the regulator. Looking for some advice of where to go next as I am at a bit of a loss.

    Cheers.
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  2. #2
    Delorean Guru
    Join Date:  May 2011

    Location:  Northern NJ

    Posts:    6,700

    My VIN:    10757

    Club(s):   (DMA)

    Sounds like you are not getting into "closed loop". The dwell (duty cycle) will fluctuate, it kind of has to and that's how you know it is working and you are in closed loop. Vacuum leaks are killers so you must get them all fixed before you can even think of measuring duty cycle let alone adjust the mixture screw. Once you fix the vacuum leaks and get into closed loop it should respond better to the throttle. Are you using the old O2 sensor or have you changed it? The old one is probably NG but make sure it is hooked up in any case. Very often they wind up being disconnected and then someone winds the mixture screw to try to compensate. Bad idea.
    David Teitelbaum

  3. #3
    Junior Member
    Join Date:  Nov 2017

    Posts:    20

    Thanks Dave. I will double check but a last known it was hooked up and operating. Never know.

  4. #4
    Member
    Join Date:  Apr 2017

    Location:  Houston

    Posts:    54

    My VIN:    1890

    I found that I could hook a voltmeter to the O2 sensor output, while watching the dwell with the dwell meter. The sensor output should fluctuate around the 0.5 v mark, and while doing so, the dwell will also fluctuate around the 50% mark. But of course that only applies when everything is working.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

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