Truck won't stay started (suspected alternator)

[thejon]

1999 Dodge Dakota Sport. V6.
It's a truck that kind of sits for a while. I usually start it about one every month or two, I usually have to charge the battery to get it going.
Anyway, this last time, it will start and run for a couple minutes and then the rpms will go lower and lower until everything shuts down. After that, nothing. Not even a dash light.
I suspect the alternator but I wanted to see if there's any other possibility before I start taking stuff apart. I know the best way is to use a meter to check the alternator but I don't really know the settings (there's several choices on volts/ohms, etc) and I don't really know the procedure. Besides that, I only have a couple minutes before everything shuts off so I did the old school alternator trick (which I know isn't good) where you take off the negative cable off the battery and if the alternator is bad, it's supposed to die. It stayed running. Is this method conclusive or does it sometimes work, sometimes not, depending on the make/model?
I know I can take the battery and alternator to a parts store to get them checked but I thought I'd post here first to see if there something I can check first. If the battery is bad, once the truck is started, it should stay running, correct?
*Oh, one more thing: my wife noticed a small spark coming from the negative battery cable when I first first started the truck after changing the battery.

 

[Ausfahrt]

If you only start it every month or two, how old is the gas?

ETA: Since you added the bit about the negative battery cable, that's a good place to start.

 

[thejon]

Kinda old... It was really low so I filled a 5 gallon gas can and put it in a few months ago

 

[Chris142]

Post a pic of your voltmeter

 

[Kira]

You need a simple tutorial on the use of a "VOM", which stands for Volt / Ohm / Milliampmeter.
It's hard to even begin to coach you through testing given your newness to all this.

Volt settings on meters are sometimes set in ranges you select among.
0-20volts for common batteries, 0-600 for building circuits.
In that larger setting, probe a house socket to see what your voltage is. It'll be a number between 108 and 120. This is your "house voltage".
In VDC (volts DC-as opposed to AC), check your battery's voltage in the morning first thing.
Start there.
Voltage in the morning is important as it's a good indicator of battery health.
Voltage while running is a good measure of alternator condition.
There are several other test points you should know.

Similarly, there are voltage tests to perform on an alternator. There are simple diode tests too.
Does your meter have a diode setting?

The pictograms used are simple and many meters use them on the range selection dial.

 

[SC Maintenance]

Easiest thing to do is to check the voltage on the battery before the start, while its running, then after the start.

This is a very crude method so it may require some additional diagnosis, however.

Before start (after you charge the battery and it rests for 30 minutes - it should be around 12.6V.

Once you start and the engine is running - the immediate voltage should show something near 14.0V. It may slowly drop down from there, but this tells you the alternator is charging - at least to some degree.

Once the vehicle stalls out, the battery should be again 12.6V+ - from being charged while the engine runs.

Probably the most important number given your battery is pretty old is the middle / 14.0V shortly after starting one.

Given you took the cable off and it ran for a time (as you know, bad idea, but nonetheless) I actually suspect a dirty ground - either at the battery or the chasis / body ground(s)? They seem to corrode when sitting.

 

[zzyzzx]

Doesn't this vehicle have a built in voltmeter in the dash?

 

[zzyzzx]

What happens if you try fully charging the battery first?

 

[thejon]

Post a pic of your voltmeter

 

[thejon]

What happens if you try fully charging the battery first?

The meter on the dash was pointed dead center. However, once the truck stalls out after a couple minutes, when I try to start it again, NOTHING. no lights, no gauges. Nothing. I charged the battery when I started and after everything stalled out and went to nothing, I took the battery to AutoZone and they said it was good, just low.

 

[thejon]

Easiest thing to do is to check the voltage on the battery before the start, while its running, then after the start.

This is a very crude method so it may require some additional diagnosis, however.

Before start (after you charge the battery and it rests for 30 minutes - it should be around 12.6V.

Once you start and the engine is running - the immediate voltage should show something near 14.0V. It may slowly drop down from there, but this tells you the alternator is charging - at least to some degree.

Once the vehicle stalls out, the battery should be again 12.6V+ - from being charged while the engine runs.

Probably the most important number given your battery is pretty old is the middle / 14.0V shortly after starting one.

Given you took the cable off and it ran for a time (as you know, bad idea, but nonetheless) I actually suspect a dirty ground - either at the battery or the chasis / body ground(s)? They seem to corrode when sitting.

Could a dirty ground or cable problem cause the spark from the negative battery cable when I first started it? Do I just go through the wiring, starting from the battery, and make sure everything is clean/tight?

 

[thejon]

Just took the battery in and it checked out ok but low (even though in the truck, it won't even light up a dash light).

 

[Hermann]

Fuel filter?

 

[SC Maintenance]

Could a dirty ground or cable problem cause the spark from the negative battery cable when I first started it? Do I just go through the wiring, starting from the battery, and make sure everything is clean/tight?

Its very strange, but I think so, given it starts, stalls, and won't even turn over, I would suspect electrical over fuel.

I would still check the voltage on initial start to see if the alternator is charging at all.

Since it will start initially, and the battery is not completely dead, then it seems like something is shorting out or not making connection after the fact. I have seen bad grounds cause all kinds of unrelated and intermittant problems. Don't ask me why. But since there is no cost associated in checking them, just time - I suggest starting there. Probably both ends of the ground cable (there are likely 3 - battery - chasis - body - all on the same cable), and both ends of the hot cable also.

 

[JMJNet]

Just took the battery in and it checked out ok but low (even though in the truck, it won't even light up a dash light).

Did you do load test? Voltage test is not a good test for battery.
To do a load test, the battery needs to be charged, then load test it after about 10 minutes after charging is finished.

Once you eliminate the battery issue, then you can test the other electrical components including the cable, alternator, etc.

 

[dishdude]

Just took the battery in and it checked out ok but low (even though in the truck, it won't even light up a dash light).

This battery sounds suspect. In this era Chrysler, if the battery is extremely dead, the PCM will not allow the alternator to charge to prevent damaging itself.

I'd try a new battery before any further troubleshooting. Also, you need a battery tender.

 

[thejon]

This battery sounds suspect. In this era Chrysler, if the battery is extremely dead, the PCM will not allow the alternator to charge to prevent damaging itself.

I'd try a new battery before any further troubleshooting. Also, you need a battery tender.

Even though AutoZone said it tested good?

 

[thejon]

Its very strange, but I think so, given it starts, stalls, and won't even turn over, I would suspect electrical over fuel.

I would still check the voltage on initial start to see if the alternator is charging at all.

Since it will start initially, and the battery is not completely dead, then it seems like something is shorting out or not making connection after the fact. I have seen bad grounds cause all kinds of unrelated and intermittant problems. Don't ask me why. But since there is no cost associated in checking them, just time - I suggest starting there. Probably both ends of the ground cable (there are likely 3 - battery - chasis - body - all on the same cable), and both ends of the hot cable also.

I'll start there. Sorry for sounding stupid but which one is the ground cable? Do I start at the negative battery cable and work back?

 

[ElectroMechanoMan]

I’ve had to deal with low batteries in Chrysler vehicles of that era and the ECMs hate a low or dead battery. They run really bad until the ECM relearns the tune. They can also run awhile and quit. Start it up and keep it off idle. After about 5 minutes, it should run ok, or at least good enough to drive it a few miles. By that time, the ECM will be happy again.

 

[SC Maintenance]

I'll start there. Sorry for sounding stupid but which one is the ground cable? Do I start at the negative battery cable and work back?

Negative / ground same thing, different wording.

The negative cable will connect to the battery and typically go from there to either the frame or the body. Often there are multiple connections on the lower end, but there might not, and there might be a second cable. You need to ensure its making good contact with all those points. However to be honest the problems I have seen are usually either to the battery, or to the chassis / frame.

Something else you can do if you don't have the manual showing the ground points - you can turn your meter to resistance - the ohm symbol on your meter just to the left of the off position. When the car quits, immediately check the resistance from the negative battery post to several points - like the frame if you can reach it, the engine, the body. It should be almost zero - ie no resistance at all. If the resistance is very high or infinite, you have a ground issue.

Have you started it and checked voltage / charge while running? I would do that first.