My 85 BII 4x4 has a 2.8 and auto trans. I recently got it running after sitting for 2 years due to an oil pump. The battery was low so I bought a brand new 850 cca battery for it. The only problem is that it kills the battery every other day or so and needs to be recharged. I am sure it is not the battery because I have already replaced it twice with the same results. I even tried a good battery out of another truck with the same results. Any suggestions?

 

The problem is probably the alternator becasuse i had the same problem. One way to check is to take a voltmeter or multimeter and test the alternator to see if it producing power. if not, you found your problem.

 

Could be a couple things...When you say the battery dies every other day, are you driving the truck, or does it die while just sitting there? Also, did you test the battery to see if it was actually discharged? First thing I would do is test the battery to see if it is actually discharged(most parts shops do it for free.)

Next there are a few things that will cause the problem you are having.
1. Check the cables for corrossion - this will keep a charged battery from starting
2. If you have been driving the vehicle, you could have a voltage regulator or alternator problem - a problem here will keep your battery from charging and you won't have enough juice to fire it up after you turn the car off (if you've been driving the truck and you take the battery in and its discharged, this is very likely) check the wiring to see if anything has come loose, or you might have to replace the regulator or alternator.

Let me know if you've been driving the truck - and when the battery seems to be discharged, take it in and have it tested to see if it actually discharged.

 

I would say that you have a dead short, basically a constant high voltage drain on the battery. This may or maynot be in your charging system (i.e. starter, regulator, alternator etc.) or it may be a pinched wire. If you didn't have this problem before the oil pump repair you may want to look over everything you did and look for a pinched wire. Electrical shorts can be challenging so be patient. Sometimes I will unhook the negative battery cable and put a test light between it and the battery. With the short, the light will be lit, then I pull fuses from the fuse box one at a time. When the light goes out then I know what "system" the short is in. Just some thoughts and I am sure you will get some great answers and guidence on this site.

 

I haven't been driving the truck. I just have it in the driveway untill I can work out all the bugs. The battery will be completely discharged after sitting for a day or two. It can be jump started with another vehicle or recharged with a battery charger and will run fine. After allowing it to run for a while, the battery has enough juice to restart on it's own. I will try pulling the fuses as suggested by 1081. thanks

 

1081, I have a stereo in my truck that has a constant hot wire to run the clock. Will this cause problems if I use the method you described? Should I dixconnect the hot wire?

 

XLNT advice from 1081. If the test light is dimly lit, thats your clock. If it's bright, theres a problem & you need to pull the fuses & relays. But cant hurt to disconnect the clock.

 

Thank you for picking that on up for me 87 XLT, that is exactly how I would have responded. Small drains for clocks and stereo memories won't run down the battery and yes the test light would have a dim light on those.

 

No problem, glad I could help. I also forgot to mention something. Dino360, if you dont allready have some good wiring diagrams, you might want to pick up an "electrical & vacuum troubleshooting manual" for your 85 from www.helminc.com for 20 bucks. It would be very handy for figuring this problem out. Keep us posted.

 

You should disconnect the battery and check the resistance from the positive battery cable to ground with a meter. This is a much better test than a test light.

An interior light, for example, would give a resistance of 6 ~ 12 ohms. This will kill a good battery in a couple of days. You should see a resistance of at least a kilohm with everything switched off. If not, start pulling fuses and watch for the resistance to increase. You have to narrow down the paths until you locate the problem.

 

When you say to test between the positive battery cable and ground do you mean the negative cable that is grounded to the motor or do you mean to run the test between the positive cable and directly to the frame?

 

They should be the same, right? There should be no resistance between the negative battery cable, the frame, or the engine. Not more than 0.2 ohms anyway. If there is you've got a bad ground path that could give you other problems, but not the drain on the battery.

You could probe this while you're at it. Disconnect the negative battery cable and test between the end of this lead and multiple ground points.

Good luck with it -- it shouldn't be too hard to track down the drain on the battery.