Announcement

Collapse
No announcement yet.

electrical shorts?

Collapse
X
Collapse
 
  • Page of 1
  • Filter
  • Time
  • Show
Clear All
new posts
Previous template Next
    #1

    electrical shorts?

    On the advice of a friend, we went ahead and tested for any shorts in the car.

    The method was to make sure everything was off, doors shut and dome lights off, pulled the plug on the hood light, unplugged the cd changer and pulled the fuses on the amp to be sure, and then took off the negative terminal and poked a multimeter between the battery post and the black wires.

    Theoretically, with nothing on, there should be no power drawn. This test makes sense to me.

    Instead, it read near the full voltage of the battery (12.6_ across the battery's terminals, 12.5_ being drawn across the negative terminal).
    On my insistence we also set it for amperage, and it read .02 Hey, at least it's not 1000 amps being drawn!

    The other symptom is that whenever I undo the negative terminal, and hook it back up to the battery, it sparks just as it makes contact.
    We measured voltage then, too: Just after sparking, we pulled the cable away again with the multimeter still probing.
    It read, this time, ~8 volts and over the course of a few seconds, climbed its way back to 12.5 volts.

    Next step, we took apart the clamp-on battery terminal that I had installed, and tested each of the cables: my added ground for my amplifier, the starter motor's ground, the direct ground to the chassis, and some smaller ground wire whose purpose I don't know. Hooked up, there was a noise from that relay/fuse box under the hood on the driver's side.

    They all had the same voltage, and all sparked when you first touched them to the battery.

    This seems to indicate that there's a short to ground somewhere, since they all share the same common ground: not that, for example, my amplifier ground cable is simply chaffed.

    I'll also add that the sparking has always been present since I have owned this car, several months now: which is a relief in that I didn't necessarily create a short in my fumbling first audio installation, but worrisome, in that I knew what I touched when I did the audio install and could start looking there.

    I recollect that last week, when I replaced my tailgate motor, I found a short where the access panels had self-tapping screws, one of which had cut into a cord there and smoked as I unscrewed it. I soldered and wrapped the damaged wire. I guess I'm looking for something else like that?

    Lastly, we started pulling fuses from the box under the steering wheel and watched the voltmeter like hawks. Nothing cut off the short; it wasn't anything controlled by one of those fuses.


    SO.
    First question, is 12.5 volts and .02 amps a problematic parasitic drain, or do people live with little faults like that all the time?
    I haven't killed the battery with it yet: just once when I know I left the lights on, and a second time when the battery was completely unhooked, so I figured the battery was on its way out.

    Second question; if a .02 amp, full voltage short is not a normal thing, and might even be a fire risk: from my above symptoms, where might it be? Not in the wires controlled by the fuse box, something that goes to the common ground, and, which after sparking, takes a couple seconds or so to build back to full battery voltage?

    I have had, 3 times, the engine quietly stall several seconds after what seemed like a normal ignition. Never on the highway, only very soon after ignition. Check engine and battery light come on, I take the key out, put it back in, start the car up, and it will again start up fine and keep running.
    Just got an obdI reader and haven't read the manual yet; but is there an electrical component possibly related to my short?


    thanks!!!
    -Bernard
    Tags: None
    #2
    you should always have the max battery voltage (or close to it) across an open. Disconnecting the battery opens the circuit. Testing from the negative terminal to any ground wire will be like testing from the same terminal to the negative cable you just removed.

    The 0.02 mA (I'm assuming it was on the lowest range) is probably the engine computer. It will have a small draw at all times for memory stuff.

    The spark as the terminal makes contact is also normal.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)

    Originally posted by gadget73
    ... and it should all work like magic and unicorns and stuff.

    Originally posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

    Comment

      #3
      Cool! Yeah, that makes sense: every time I disconnect the battery I lose my clock time, and my head unit forgets my saved favourite stations

      Comment

        #4
        digital multimeters will show nearly full voltage when hooked across a circuit if it has even the tiniest current draw. The ammeter function is far more useful. You won't see zero draw on anything more advanced than a mid 60s Fairlane. The ECM's keep-alive memory, the radio station memory, the clock, and various other modules in the car all pull a tiny bit of power. 0.02 amps (or 20 ma) is low enough to be considered normal. If the car can sit a couple days without the battery being dead, you're fine. I can get 2-3 weeks out of my car before the small draws will make it not crank.

        The stalling right after startup may be a sticky IAC or a faulty temperature sensor. It may not throw a code, but you can meter out the temperature senders to see if the values match the charts at fordfuelinjection.com.
        86 Lincoln Town Car (Galactica).
        5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

        91 Lincoln Mark VII LSC grandpa spec white and cranberry

        1984 Lincoln Continental TurboDiesel - rolls coal

        Originally posted by phayzer5
        I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

        Comment

          #5
          digital multimeters will show nearly full voltage when hooked across a circuit if it has even the tiniest current draw. The ammeter function is far more useful. You won't see zero draw on anything more advanced than a mid 60s Fairlane. The ECM's keep-alive memory, the radio station memory, the clock, and various other modules in the car all pull a tiny bit of power. 0.02 amps (or 20 ma) is low enough to be considered normal. If the car can sit a couple days without the battery being dead, you're fine. I can get 2-3 weeks out of my car before the small draws will make it not crank.

          The stalling right after startup may be a sticky IAC or a faulty temperature sensor. It may not throw a code, but you can meter out the temperature senders to see if the values match the charts at fordfuelinjection.com.
          86 Lincoln Town Car (Galactica).
          5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

          91 Lincoln Mark VII LSC grandpa spec white and cranberry

          1984 Lincoln Continental TurboDiesel - rolls coal

          Originally posted by phayzer5
          I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

          Comment

            #6
            you have an 89 right? well i dont know if you have an external voltage regulator or not. but ive seen alot of these where the wires going into the pigtail that plugs into the external regulor get all funky and break. this can cause many sleepless nights. if you look in there and see corrosion id change it. they used to sell these pigtails at parts stores. just cut the wires on the old one and splice and shrink tube the new one. its been a long time for me so i cant remember if this caused issues like this.
            My wife and I.sigpic

            Comment

              #7
              Thanks for the advice! My friend nash has helped me out on a few things, but I dare say this is one point where he's wrong. He also insisted that the valve cover bolts were somehow metric, even though I swore it was a perfect match to 1/4-20!

              I just got a quick-disconnect terminal-- I spend enough time working on my car anyway, that it's a good idea to not break the terminal wiggling it off and on all the time. Not that I'm likely to leave it fully 2-3 weeks undriven, but it'll be there.

              Comment

                #8
                that's a great site btw, gadget!

                I do trust my temperature gauge on the dash; it behaves like it should. Does it rely, however, on readings from multiple temperature sensors, any one of which could be bad?

                Will investigate the IAC tomorrow.

                Comment

                  #9
                  the computer temperature sensor and the gauge sensor are different. The ECM sensor is a 2 wire sensor in the fitting at the front right corner where the heater hose connects. The gauge one is on the front left corner, single wire thing.
                  86 Lincoln Town Car (Galactica).
                  5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                  91 Lincoln Mark VII LSC grandpa spec white and cranberry

                  1984 Lincoln Continental TurboDiesel - rolls coal

                  Originally posted by phayzer5
                  I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                  Comment

                  Previous template Next
                  Working...
                  X