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Thread: Wur resistance

  1. #1
    Senior Member Beachdrifter's Avatar
    Join Date:  May 2011

    Location:  Space Coast, FL *USA*

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    My VIN:    * 5945 * Oct, 31, 1981. FranKenDeLorean

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    Wur resistance

    Hi all,

    I've heard that the resistance across the two pins of the WUR should be 20 ohms. I assume this is taken with the car off. When I did, I was getting a reading of 40.

    Is that ok or is that an indication that my wur is bad?

    Thanks.
    ** A wave is like an empty canvas, waiting for a masterpiece -- unknown **
    ** VIN 5945 - FranKenDeLorean Oct 31, 1981 ** SpaceCoast, FL, USA ** DMCTalk Member/DMCOwner Since 2005

  2. #2
    Senior Member
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    The true measure of function is the WUR's ability to lower the control pressure when cold and maintain when warm. If the control pressure follows the measurements in the workshop manual, then it doesn't really matter what the resistance of the heating element is.

  3. #3
    '82 T3 FABombjoy's Avatar
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    Agreed - measuring either open (infinite) or short (0 ohm) would be a concern. 40 vs 20 is probably not worrisome unless the pressures are off. 20 ohms would heat up a bit faster. 40 ohms would be gentler on the wiring and connectors.

    The pressure chart has a wide margin too. Even if pressures vary a bit from book range, if the car drives well during & after warmup its still probably OK.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  4. #4
    Senior Member
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    I’m going to admit to something terrible here. Lol. I’ve been running my car for quite awhile now with the WUR unplugged. I found mine had a direct short and was cooking my RPM relay. So I unplugged it till I got a new one. I didn’t like sending mine in to be rebuilt and was looking for a complete unit to buy outright.

    The interesting part is there’s almost no difference in it’s operation in hot weather. The heat from the valve cover warms it up and it runs fine. When it’s cold out, it noticeably takes longer to run right. (About 5 minutes) I have not driven the car in sub freezing weather. I suppose it could get cold enough that it would never increase the control pressure. I live in Florida and I’ve not got to that point yet. The way it runs, I’m not in any rush to fix it.

    I also have to admit that I rebuilt mine when I first got the car. It maybe that I assembled it in such a way that I caused the direct short. In fact, one terminal is around 20 to the other. The problem is one terminal is a direct short to ground. (Neither should be grounded) So probably I have simple fix if I take it apart. It just hasn’t been a big issue and I have so many other projects to work on.

  5. #5
    Senior Member
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    The wur aka Control Pressure Regulator, works like a choke. Unless it is very cold the car will run with a defective one. Once you warm up it has no effect. It does sense heat from the valve cover, the electric heating element is to get it to lean out the mixture faster. It's an EPA thing to shorten the warm-up cycle.
    David Teitelbaum

  6. #6
    Senior Member
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    Quote Originally Posted by Helirich View Post
    I’ve been running my car for quite awhile now with the WUR unplugged. I found mine had a direct short and was cooking my RPM relay. So I unplugged it till I got a new one.
    Dave McKeen came up with a solution to prevent a malfunctioning WUR from frying the RPM relay. He puts a 3 amp fuse on the positive WUR wire.

  7. #7
    Senior Member
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    Quote Originally Posted by CFI View Post
    Dave McKeen came up with a solution to prevent a malfunctioning WUR from frying the RPM relay. He puts a 3 amp fuse on the positive WUR wire.
    Dave’s rpm relay was how I found out about my direct short. The stock relay always gets hot, but when Dave’s got hot, I knew something was wrong.

  8. #8
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Helirich View Post
    Dave’s rpm relay was how I found out about my direct short. The stock relay always gets hot, but when Dave’s got hot, I knew something was wrong.
    It funny the 20 amp fuse does not blow when the WUR heater shorts. I just guess the wiring small gauge gives it enough resistance to not blow that 20 amp. Since the fuel pump draws about 7 amps that leaves 13 amps for the WUR. But a fuse will not blow till it sees above the rated current for some time.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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