battery drain

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  #1  
Old 01-30-04, 08:25 PM
smhodge
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battery drain

1991 Ford F-150XLT truck (6-cyl, 5-spd manual, 4WD, 140000 miles)

Symptoms: (1) battery drains over a period of days; (2) factory radio has dimmed display.

My father (previous owner) spent quite a bit of money to get a new battery, fuel pump relay, and a disconnected radio. It starts easily, runs great, and everything seems to work fine (lights, etc.). Voltage is 14.x (didn't note it) with engine running; 13.x with lights, fan, and radio on.

With battery at 12.6 volts, I connected a multitester in series from ground to neg battery terminal. Measured 0.3 amps (0.304 - 0.308 with truck off, and for comparison 1.3A with driver door open (cabin light). Measured amps with (1) hood closed (engine compartment light), (2) after radio disconnected, and (3) one-by-one pulling each fuse in the box. The readings didn't move outside of the 0.304-0.308 range.

The Haines manual has a charging system check item: "With the key off, connect a test light between neg battery post and the disconnected neg cable clamp; if the test light comes on, there is a short in the system." I measured 12.6 volts, which didn't change when any one fuse was pulled.

Don't know where to go from here. There is a distinct click and short whirring sound (< 1 sec.) from the driver-side of the engine when connecting the battery. I didn't notice any other sounds during the testing. Pulled the battery tonight to charge it and found it was frozen, so I'm replacing it tomorrow. I may have compounded the problem by frequent jump starts and driving just to recharge the battery, so the alternator might be suspect.

Any ideas/methods you could suggest would be greatly appreciated.
Thanks!
 
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  #2  
Old 01-30-04, 09:31 PM
mike from nj
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.3 amps is too high. ideally you want .030 amps. (30 milliamps and under)

you need to disconnect everything electrical to determine the draw. including the computers, relays, and the alternator. here's where a 'real' manual shines, not the cheap imitation ones

sometimes there are timer modules that need to 'time out' for the system to go to 'sleep'. when they don't, you have a draw.

one way i trick the modules to 'sleep' (on my brand) is to have the ammeter hooked in series like you have, and hold the battery terminal wire on the battery to let them time out, then break the connection of the battery, but never losing the ammeter connections. they are maintained throughout the process. (i use a jumper wire with alligator clips to make the battery connection) sometimes it can take a few minutes, the service manual should tell you how long.

i'm not real familiar with fords, maybe someone with some specific experience can help you here. just offering my advice.
 
  #3  
Old 01-31-04, 04:02 AM
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Mike was right on with all his advise but let me clear up what he meant by "disconnect everything electrical". Assuming your fuse box is under the dash, disable the door jam switch somehow to stop that from triggering anything. Now start pulling fuses one at a time until your test light goes out. Now you have narrowed it down to what circuit. What you have to do now is find out what feeds on that fuse and start disconnecting individual components until you find the culprit. Like Mike said, modules are common problems, like trunk lights and glove box lights.
 
  #4  
Old 01-31-04, 04:35 AM
Join Date: Jun 2002
Location: Long Island, NY
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I vote for disconnecting the Alt Bat wire. Have seen on Fords where a diode is partially shorted causing a drain.
 
  #5  
Old 03-01-04, 02:11 PM
smhodge
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fuel pump relay

After finding nothing wrong with the circuits going through the fuse panel, I decided I didn't know enough to mess around with the electrical under the hood and took it in. I also needed a "certified" fix since it's for sale.

The power-draw turned out to be the fuel pump relay, which has been the culprit before. Wonder if it has anything to do with the dual fuel tank system.
 
  #6  
Old 03-01-04, 02:53 PM
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Originally posted by toyotaman11769
I vote for disconnecting the Alt Bat wire. Have seen on Fords where a diode is partially shorted causing a drain.
I have too but it's usually a much larger draw that 300ma and kills it in a matter of hours. If I haven't found anything with the fuses, I usually go there next.
 
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