Odd Parasitic Draw, 1996 Contour

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Whimsey

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A while ago I posted that I replaced a 6 1/2 year old battery that sat for 3 weeks without starting because the voltage dropped to .03 Volts, I figured it was just old. I got a Motorcraft battery and all seemed fine till it sat for LESS THAN 3 DAYS. The battery was totally dead and the voltage was again .03 volts. I figured a bad new battery with a dead cell most likely. Took it back to the dealer and after charging it overnight and doing their tests they determined the battery was fine. I've had it in the car with the ground disconnected for the last 2 weeks. The battery has held 12.6 Volts the entire time. The strange thing is the parasitic draw varies from .018 Amps to .9 Amps when I tested over these last 2 weeks. Oh, and the battery voltage at idle was 13.7. Since it drains SO quickly and the parasitic drain test is not real high I'm thinking something more than a light or switch. The car is a stripper, not much power accessories at all. I've read that an alternator with bad diodes can quickly kill a battery if it sits. Any thoughts would be greatly appreciated.
Thanks!

Whimsey
 
I had a '97 Taurus that had a 1/2 amp draw. Turned out to be the 'football' they used for climate control and radio.
 
My dad's old Ford Windstar had this problem and we found it was a bad diode that was installed like a fuse in the fuse box located under the hood. I forget what this was for but it was causing the problem. He replaced it and all was good. Just in case you have a similar setup you can check that as well.
 
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Originally Posted By: WobblyElvis
Eric the car guy has a good video on chasing down parasitic draw. I would give it a try.

https://www.youtube.com/watch?v=KF1gijj03_0


Wobbly you gave me this link previously and I watched, thanks, it was a great help. My problem is the parasitic draw doesn't seem enough to kill a new fully charged battery to .03 Volts in less than 3 days of sitting. There has to be something more major going on. And why the variance in the parasitic amp draw from one day to another without doing anything different for 2 weeks with the battery ground disconnected the entire time? I read that the diodes in the alternator act as a one way switch and if they fail they can drain a battery quickly. But I would assume that would show up as a parasitic drain, could be wrong though.

Thanks, Whimsey
 
Here is how to check the alternator diodes in case that is what the problem is. I have seen them cause problems intermittently like they are slowing going bad. It's rare that they don't just fail completely but it does happen.



Around 1:20
 
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I'm looking at the under hood fuse box diagram and listing from the OM. It lists a D1 that is a "reverse voltage protection". All the other fuse/relays start with a R, This one is listed as a D, maybe for Diode. I'll call the dealer tomorrow to see if they have a better idea and hopefully I can still get it. Thanks a lot!

Whimsey
 
Good luck!
thumbsup2.gif
 
If it is still the original alternator, definitely rule that out first.

You can test by simply looking for ac voltage at the battery, one sign of a failed diode. Most all auto parts stores will test it for free for you with a clamp-on diagnostic tool, also.
 
Originally Posted By: Whimsey
I'm looking at the under hood fuse box diagram and listing from the OM. It lists a D1 that is a "reverse voltage protection". All the other fuse/relays start with a R, This one is listed as a D, maybe for Diode. I'll call the dealer tomorrow to see if they have a better idea and hopefully I can still get it. Thanks a lot!

Whimsey
FYI the reverse voltage when the AC compressor clutch turns off can be 50+ volts !!
 
One thing peculiar to that specific model/year is the wiring harness problems. FoMoCo had a program/recall on the underhood wiring harnesses due to insulation degradation. Chances are it has been done, but just maybe something to check on. You can easily tell by examining the insulation on the underhood harness to check for cracking.

Ditto on the post above checking for AC output at alt when engine is running. Good tip. The most basic DVOM will pick up on it. Good luck with it.
 
Originally Posted By: punisher
One thing peculiar to that specific model/year is the wiring harness problems. FoMoCo had a program/recall on the underhood wiring harnesses due to insulation degradation. Chances are it has been done, but just maybe something to check on. You can easily tell by examining the insulation on the underhood harness to check for cracking.

Ditto on the post above checking for AC output at alt when engine is running. Good tip. The most basic DVOM will pick up on it. Good luck with it.


Thanks, I'm the original owner and the wiring recall was not done because at the 10 year limit they were not "rotted" per 2 dealers. Living in NJ with our climate has been "gentler" on the wiring. Though one of the cables, not the big one, off the positive battery lead was exposed in a section. I used the liquid wire to close it up. The other wires I can see look ok. I'll check the AC voltage off the alt tomorrow and let all of you know what I find. Again thanks to all for your help.

Whimsey
 
I had a 97 Contour and one of the relays stuck closed/on, it was for the ignition module. Swapped it for the horn relay (!) b/c I figured at least I'd know if that one went bad. Oddly everything worked great after doing that.

I opened the hood on a quiet morning and just heard the module buzzing, like an old TV.

With your car you could probably pull half the maxi-fuses one day then the other half the next then narrow it down from there.

If you have an IR thermometer the part guzzling power should be a few degrees warmer on a cold morning.
 
Put your meter on it and start pulling fuses, should be obvious when the draw is eliminated.

On old Ford's I've had the alternator poop the bed as StevieC touched on, but usually they "charge" at an insanely high voltage, which is a big red flag. These were all 2G though, never had that issue with a 3G.

On the Expeditions and F-150's the ABS pump would have one of the internal relays fuse shut and run the pump which would kill the battery. Had that happen on ours, so we ran it without ABS for quite a while.
 
Originally Posted By: JHZR2
You sure it’s not a bad diode in the alternator?


No I'm not, With it draining the battery to .03 volts in under 3 days of sitting it has to be something severe. The parasitic draw I've been monitoring runs between .018 Amp to .9 Amp. I don't think such a low draw from say a light or switch could totally kill the battery that fast. I'll test the AC voltage on the battery per the test video in this posting and let you know. I know bad alternator diodes can drain a battery fairly quickly, but does it show up as a large parasitic draw? The alternator is original, so it's 22 1/2 years old.

Whimsey
 
My old BMW had two battery draining issues within about a month of each other. The first time was just after I replaced the trunk gasket and my daughter didn't make sure the lid was latched and that caused the lights to stay on. The draw was 0.45A.

About a month later it drained the battery again and was about 0.5A or so. This time it was the alternator diodes. I found that out by pulling all the fuses and yet there was still a draw. The alternator draws cooling air in through a duct to the front bumper and it was chock full of insects and other junk. At the time the alternator was about 21 years old.

FWIW on my BMW the draw is relatively high when the car is first shut off but then steps down in several stages over about a minute or two. The maximum quiescent draw is defined in the service manual somewhere but IIRC it was around 0.02A.
 
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