2nd Gen Non-Engine/Transmission Batteries draining.

[Erniek]

I have a 97 extended cab 2500 4wd. I have a problem with my batteries draining overnight. They drain enough that in two days, the truck will barely crank hard enough to start. I have isolated the problem to the fuel pump circuit. I say this because when I pull the large square blue 20 amp fuse that is labeled "fuel pump" per the owners manual, that is located in the power distribution box under the hood, the batteries will stay charged overnight and beyond. The truck will start with that fuse pulled, but I have some warning lights on the dash illuminated when it is running with that fuse pulled, one of which is the "GEN" light. (I know this because I forgot to plug it back in this morning when I first started the truck.)Has anyone else seen this same problem? Could I have a bad fuel pump that is drawing power with the key off and removed?? Or maybe a shorted wire somewhere in that circuit? The truck runs fine once it gets started, and the alternator is putting out 14 volts, checked at the batteries. The batteries are brand new Die Hards, as I replaced the old ones thinking my problem was the Batteries. Any Ideas???

Thanks in advance for any help,

Erik

 

[Road Dog]

In a '97 the injector pump and lift pump are 100% mechanical. The fuse is for the fuel pump on a gasser and I guess for something else on a Diesel.

 

[Erniek]

OK, thank you, those are both mechanical. There is a wiring harness plugged into something on the top of the fuel tank. Could there be a pump in the tank, or is that for the gauging system?

Erik

 

[Road Dog]

It's for a fuel level sensor.

 

[Erniek]

anybody know where I can find a wiring diagram for my truck?

 

[B.G. Smith]

The fuse that would be the fuel pump on a gas rig is the charging line from the alternator on the diesel I believe. If the fuse is 120 amps then that is it. If that is the case you may have a bad diode in the alternato which is draining the batteries. Try removing the large wire from the alternator and touch it back to the terminal it fits on and see if there is a spark. If so then the alternator need attention. bg

 

[Erniek]

Thanks BG and Road Dog. I found a chrysler manual for my truck and located the wiring diagrams. The fuse that stops the drain is the blue 20 amp one. It is labeled Fuel. From what I can see in the diagram this supplies power to the Fuel Pump Relay, the Transmission Relay, and sends power to the PCM. We have established the Diesel doesn't have a fuel pump, so that is eliminated. My truck is a manual transmission so the transmission relay circuit is eliminated. That leaves the PCM. Has anyone ever seen a PCM go bad and just start bleeding the batteries dry?? Can the PCM's be tested??

Thanks, Erik

 

[Erniek]

Update:
After more trouble shooting today, by that I mean installing a volt meter between the power lead from the Batteries to the Power distribution center under the hood, then pulling all the fuses one by one until the voltage reading of 12.45 volts (this is what is draining my batteries) goes away, i found that when I pull the blue 20 amp fuse i referred to in previous post, the voltage draw drops to about 12.25 volts. After pulling the rest of them, I found the only other one that had any effect was the Red 50 amp one that is labeled park, Ign. When I pulled this, the voltage draw dropped to zero. That fuse feeds two other fuses in the PDC and several in the fuse block inside the cab. Now it looks like I have more digging to do!! If I ever find the culprit, I will post my findings. Until then I guess I will keep pulling that fuse whenever I park for the night.

Erik

 

[Cosmo]

When checking for a draw, keep in mind the timer module. It stays awake for what, 30 minutes after last disturbed?

 

[Road Dog]

The 50A fuse might be the Ignition Off Draw and it's main purpose to to totally kill the power when a new vehicle is shipped across the country or when it's being stored for a long time. It's for all the circuits that never turn off (pcm, timer module, air bags, seat belts, radio, etc).

 

[B.G. Smith]

As you probably already know, you would be way ahead on finding the drain with an amp meter, with everything off you wouldn't need but about a 10 amp unit. The IOD fuse is much smaller than the 50 I think, probably 10 amps or less. bg

 

[JMcCoy]

I recenty faught this fight. It turned out to be the alternator. It was charging good, but must have had a bad diode. The PCM controls the alternator charging so that may be why that fuse circuit is showing the draw. I would take the alternator to a "competent" alternator/starter shop and they can test it. The high school drop-outs at Discount Auto Parts, Napa, and Bennett was unable to test mine. The one at Pepboys was able to work the register and sell me one for $95 thought. All is fine now.

 

[Erniek]

Thank's everybody for your help. I haven't had time recently to do anymore troubleshooting, so I still haven't found the problem. JMcCoy, thanks for the idea, thats what I was hoping to get, a story from someone else who had experienced the same problem, and what they did to fix it. I will be taking my alternator to competent shop for testing this week.

 

[Erniek]

Well, I finally got a chance to work on my truck. It turns out it was a bad alternator, just like JMcCoy said he recently had. I tested the idea by disconnecting the alternator and letting the truck sit for several days. The batteries stayed charged! I got another remanufactured unit from O'reilleys at no cost, as the bad one was a lifetime warranty unit I had replaced several years ago. I explained to the guy behind the counter what I did to trouble shoot the problem, and he took me for my word and just replaced it with no hassles. I asked him if they had a tester that could check the diodes inside the unit, and he said nope, just a way to test the voltage output. I'm glad he took my word for it. I changed it out several days ago, and after sitting in the drive way for two days without starting or charging, the batteries are still up to full charge at 12.65 volts.
Thanks for the idea JMcCoy!

Erik

 

[B.G. Smith]

Well, I finally got a chance to work on my truck. It turns out it was a bad alternator, just like JMcCoy said he recently had. I tested the idea by disconnecting the alternator and letting the truck sit for several days. The batteries stayed charged! I got another remanufactured unit from O'reilleys at no cost, as the bad one was a lifetime warranty unit I had replaced several years ago. I explained to the guy behind the counter what I did to trouble shoot the problem, and he took me for my word and just replaced it with no hassles. I asked him if they had a tester that could check the diodes inside the unit, and he said nope, just a way to test the voltage output. I'm glad he took my word for it. I changed it out several days ago, and after sitting in the drive way for two days without starting or charging, the batteries are still up to full charge at 12.65 volts.
Thanks for the idea JMcCoy!

Erik

Do my comments show up on your computer? Thanks. bg