Engine/Transmission (1994 - 1998) Electrical problem

[DWJoy]

I have a 96 12 valve 2wheel drive auto with 180,000 miles. The batteries go down after truck sits 8 to 12 hrs. They hold 12. 4 volts but will barely start the truck. I replaced the batteries because was told they were bad. 1 had 2 weak cells the other would not hold up to a load test. 4 days later I have the same problem. I think I must have a draw some place. It turns over hard after it sets but after you run it for a few minities and leave it set for a short time it cranks over good. The altinator is charging at13. 8. Any one had this problem? Where could I start to find what is drawing down the batteries?

 

[fest3er]

If you have a fuse box under the hood and there is an alternator fuse (maybe 140A) in it, remove that fuse and let the truck sit for 8-12 hours. If the battery voltage is OK after 8-12 hours, your alternator has a bad diode. If you have a VOM, you could measure the resistance between the alternator's battery lead and ground; if it isn't open or at least in the mega-ohm vicinity, you'll have spotted the bad diode without waiting 8-12 hours.

If that ain't it and you have a VOM, you can pull fuses one at a time and measure the voltage across the two contacts (making a 'plug' from an old blown fuse would make this easier). If you see no voltage, that circuit is properly turned off. Otherwise, circuits that draw a little power (like the radio's clock) should should very low voltage, circuits that draw a LOT of power should show near battery voltage, and your miscreant circuit might show 5-6 volts.

Your alternator is the primary suspect.

 

[DWJoy]

Neal

I found the fuse. it is 120 A. Is their a trick to remove it?

After setting 10 Hrs. my volt meter said 12. 5 volts and the starter turned over slow but started. After idleing for 5 minutes shut it off and it cranked over strong. If the batteries are down should they be less than 12 volts? I am not sure what you mean by a VOM or how to test resistence. I have digital mulitmeter that tests VDC OHM ADC VAC. Can I use this to check resistence?



Thank nyou for the help

Don

 

[Wingate]

VOM is a volt-ohm meter.....

If you have a decent meter, you can disconnect both batteries, then put the meter inline from one battery positive post to the cable, set the meter for DC amps. The reading on the meter at this point will be your drain. Start pulling fuses one at a time until you see the amperage drop. At that point, you will have it narrowed down to the sub-system thats causing the dead battery condition. Then you can consult the fuse nomeclature and see exactly what all is on that circuit. You might have to get a service manual if it gets really in depth.

Sometimes its something as simple as a radio amp that is mis-wired and staying powered up all the time.

I recently found one that was due to a rear door courtesy lamp that was staying powered up all the time.

Also, watch for under hood lights!!!!. . Seen that one happen also.

 

[fest3er]

Neal

I found the fuse. it is 120 A. Is their a trick to remove it?

After setting 10 Hrs. my volt meter said 12. 5 volts and the starter turned over slow but started. After idleing for 5 minutes shut it off and it cranked over strong. If the batteries are down should they be less than 12 volts? I am not sure what you mean by a VOM or how to test resistence. I have digital mulitmeter that tests VDC OHM ADC VAC. Can I use this to check resistence?



Thank nyou for the help

Don

The fuse is probably screwed in. On my '98, there is a screw forward and aft of the fuse; remove the screws and the fuse should come out relatively easily.



Sorry. Too much time around Dad: he's been a ham since '42, and uses a lot of oldtime terms, like VOM. You have a DMM, which is the modern equivalent. Wingate's got the right idea. Set the meter on DC current (ADC, which likely means Amps, Direct Current).



First, be sure both batteries are reasonably charged. Disconnect both battery negatives. Then clamp/affix the red DMM lead to one clamp and the black lead to the battery post. Then check the other battery and clamp. If you don't see more than 20-50mA of current at either battery, you might have a shorted battery, which will drag both down. If you see 2-10 amps of current at both batteries, something is definitely drawing current. Then do what Wingate suggested: check fuse-by-fuse until you find the culprit.



As to measuring resistance. If you set the meter on OHM, and disconnect both negative battery clamps, you can connect the black DMM lead to any body/chassis ground and the red lead to a suspect circuit. If it reads 1,000 mega-ohms (or is flashing), the circuit is open and won't draw current. If it reads 0 ohms, it's a short circuit and will drain the batteries extremely fast (for example, frame-to-body should be a short circuit; but it's probably closer to 4 ohms). You could even measure the resistance of an incandescent bulb (brake light bulb, for instance). It might measure around . 5 Ohm; if it's open, it shouldn't light up. If it measures 0 ohms, it's shorted and should blow the brake light fuse when you step on the brake.



Generally speaking, the lower the resistance in the circuit, the more current it will draw. Very high resistance indicates almost zero current draw. Even 10K ohms won't draw much. 12 ohms draws about an amp. 1. 2 ohms is about 10A. 0. 1 to 0. 2 Ohms, yer lookin' at MANY amps of current. Measure the resistance across one of your intake heaters; it should be about 0. 15 ohms, because each heater grid draws 100A of current.

 

[GAmes]

If one or both of the grid heater relays stick closed they will drain a battery very quickly. Since they employ a fuse wire I do not believe they have a conventional fuse. Disconnecting one small wire from each of the relays is an easy way to eliminate or confirm them as the problem.

 

[fest3er]

If one or both of the grid heater relays stick closed they will drain a battery very quickly. Since they employ a fuse wire I do not believe they have a conventional fuse. Disconnecting one small wire from each of the relays is an easy way to eliminate or confirm them as the problem.

At 100A each, one will drain the batteries quickly; both will drain the batteries in half the time. I think one of my relays stuck closed years back, drained both batteries in about 40 minutes, and melted stuff on the intake manifold, including the boost line to the AFC. (Speaking in ballpark figures, draining the batteries in 40 minutes at 100A demonstrated that my OEM batteries could produce 150A for 1 hour, or 15A for 10 hours. ) (As another aside, it looks like it's been 8 years now since I installed the Stancor replacement relays and have never had a single problem with them; they work and sound the same as they did when they were brandy-new. The OEM relays are notoriously marginal. )



Disconnecting a relay control lead won't necessarily release a stuck relay. If the control circuit is isolated from the frame, one might be able to reverse the polarity of the control leads and force the relay to disconnect. Whacking the relay with a wooden stick might dislodge it (put it back in whack). But since the OP's problem is regular and takes hours to drain the batteries, it's not likely to be a bad relay.

 

[Grumpy John 4x4]

Battery problems

My problem was simple had a short in my wiring going towards back bumper!

 

[DWJoy]

After seting 12 hr. volt test shows 12. 5 battery shows 80% charge turned over real slow but started.

I did the test Wingate and fest3er sugested with meter set on ADC and got 0 reading on both positive and negative side. Does this mean I have no draw or I am doing something wrong?

Is it posible I have a starter problem? I would think it should crank good with 12. 5 volts and 80% charge.

 

[GAmes]

Disconnecting a relay control lead won't necessarily release a stuck relay. If the control circuit is isolated from the frame, one might be able to reverse the polarity of the control leads and force the relay to disconnect. Whacking the relay with a wooden stick might dislodge it (put it back in whack). But since the OP's problem is regular and takes hours to drain the batteries, it's not likely to be a bad relay.

You are correct. Had a senior moment. I have Stancor relays as well, about 6 years on mine. The originals failed while the truck was still under warranty, but I wasn't there to see how fast the batteries discharged. My wife had driven it to VA to visit her mom. The local dealer in Newport News took advantage of the fact that she was a woman with no clue and charged her for the parts, but not the labor Those failed a few years later, after I had joined the TDR, so I was informed about the new relays.

 

[LVJUNIOR]

DWJoy if you find the problem could you let me know. I have very similar battery drain and have been unable to find the culprit. The batteries have been unhooked for three weeks and are still holding steady

 

[DWJoy]

I will post what I find is the problem if I ever figure it out. Tonite I have removed the alternator fuse to see if the batteries go down. I charged both this afternoon and it set for 6 hrs. and still shows full charge. I will check in the morning if it is still full charge I guess it is the alternator. Next thing I will do is take it to Advance auto parts. I found out they will check the battery, starter and chargeing system for free. I kmow for free you always get your moneys worth but it is worth a try and see what they find.

 

[DieselDoghouse]

Let us know how you make out. They can test it roughly - they are not equipped to check for a single bad diode (possibly your problem)— you'd need an oscilloscope OR a 'puter that can read waveforms. Your alternator is a set of (ideally) triplets - three exatly equal windings that produce output directed by a pair of diodes for each. Lose one diode on a winding and it becomes the 'bad seed' (for half a cycle) absorbing energy from the other windings instead of pulling its weight. Sound strange?? Alternators are AC inside and DC outside - and the the 6 diodes are the key to all the energy moving in the same direction—forcing each winding to output EMF or 'wait its turn'. The problem for (not with) auto parts store folks - a bad alternator can output 12V - just not 12V @ rated current! With a scope you can see the missing waveform like a lost tooth and identify the problem - but that's automotive electronics shops! Why so complicated?? it has been the only way to generate rated current output regardless of engine speed (largely), with alternators what changes with speed is the frequency of the AC energy and after the diodes are done we don't care!!—we got 14. 4 volts DC and everythings running!

 

[PToombs]

If you use a test light instead of a multi meter you can see in an instant if you have a draw. If you do, it will light. If you suspect the alternator, unplug it, and the light will go out if it's bad. It may flash quick and then go out, this is normal. It's the computer or memory on the clock.

If the light is bright, it's a big draw, if it's faint, it's likely something small.

 

[fest3er]

I will post what I find is the problem if I ever figure it out. ...

BTW, where you at? Anywhere near VA/MD/PA?

 

[DWJoy]

Up date. Everything tested good. Batteries hold up but still turns over slow sometimes. Seems like a starter problem now. Changing the starter today.

 

[DWJoy]

I replaced the batteries and the starter and it is starting good. Thanks for all your help.