Don't overthink this issue. You have 3 components to your charging system. The alternator puts out voltage and current. The cables transport it and the battery(s) store it.

1 of those three component is bad. Simple as that.

Get a volt meter and measure your voltage at the battery, engine off. Now, start the engine, Did the voltage go up a few volts? If so, then the alternator and cables are doing their job and the batteries need to be replaced. If not, the alternator or cables are bad.

 

The 4th component is the instrument cluster and I circuit. I mentioned it because a guy here (or in the 6.0L forum) had a charging problem that ended up being caused by a bad cluster.

 

Oh the suspense! I love mysteries!



Hello DCChamberlain! I see we're in the same neighborhood. Or there abouts. I'm north of Eugene.


I drove through Lake county in my classic many years ago heading to CO for a summer job, decided to take the scenic route. It was an amazing trip. It's very desolate through those parts. Had me a bit worried. At that time my classic was all original and I was a tad worried she'd be a little unreliable. Not to mention I heard on the radio during my trip about some census workers back in the day that got lost in eastern OR trying to find people to count.

 

There are no people out here. We're just figments of your imagination. Unless you have money, then you're welcome to spend it on your way through. I'm always amazed at the people who go whizzing through here absolutely oblivious to what I consider some pretty amazing scenic beauty. All they see is the sagebrush.

I used to live in the valley. I moved here to get away from it. I went to Bend today and there are too many people there now for my comfort.

For the trivia buffs. The population density for Lake County, OR is .97 persons per square mile, and there is not one stop light in the entire county. The size of the county is 8,139 square miles. That's larger than Rhode Island, Delaware, Connecticut and New Jersey (individually, not combined). We average less than 16 inches of rain per year. Altitude accessible by road varies from 4300 feet up well past 8000 feet (depending on your definition of "road").

 

Ok im sure if the batts were discharging at "welding current" rate he would have seen the problem already... honestly I would bet his truck burnt down by now... anyway, read the advise and "get er dun" elect gremlins are a pain, but doable... And as for you Squatch... that mystery statment made me LOL this morn... good on you!

 

Why would the truck die after it is started because of a bum battery? Assuming the alternator is good and connected to the battery properly the truck should be running off the current the alternator is putting it out after it is started and not off of the battery.

The base 157A alternator in the SD diesel should have no trouble putting out the 40-60A you reference above at idle.

Of course if you have a halogen rotator light bar running, rapid heat on, sliding rear window defroster, and full lights on you may need more than that and that is why we have heavy duty alternator and dual alternator options.

I am not dismissing your idea as if he has enough loads on the truck the loads could be outrunning alternator output BUT I think the most likely causes is that the alternator is not putting out enough juice OR it does not have a solid good connection (both hot and ground) to the battery. This could be choking current output.

If, because of a bad alt or connection fro alt to battery, it is only putting out 10A-20A of charge current at idle then the scenario you describe above is completely possible.

---Aaron

 

Who is assuming the alternator is good? And I didn't say bum battery, I said discharged battery.

The stock alternator is 115A, according to my service manual, which is for a 2004. I have heard people say 110A also.

Which is exactly the point I was making.

 

Just to put my to friggin cents in.... I have seen bad batteries make vehicles with good alternators shut off.

Now thats just a fact. ***DISCLAIMER*** I am not saying this is the guys problem, but it is possible.

You can tell this is the problem because after you jump it, when you disconect the jumpers... the vechicle dies immediately. This happens cause the system needs a loop, and the batt turns into an open...

 

You still have a 'loop' (complete circuit) and that is the alternator. An alternator is a current and voltage source just like a battery. You can remove a battery in almost any circuit and replace it with a DC power supply sized for the loads and it will work just fine.

The battery in a vehicle is used to start it and to provide additional current in the event the loads temporarily exceed the ability of the alternator to supply current to run the loads, such as when at a stop light with the defroster on, stereo cranking, headlights on etc.

However, to your point, if the battery is so messed up it is an 'open', or if it is a total short, or if it has a dead cell and tries to pull the alternator and second battery down to 10V instead of 12V, all bets are off.

The OP stated that he can start his truck, and it runs for 20 minutes before the lights start to flicker, gauges go out, and the truck stalls. This is not the symptom of a battery that you describe above but is a classic sign of an alternator not being able to keep up with demand and batteries that are not fully charged (or possibly even damaged) because of prior alternator problems. I am not saying his batteries are AOK and in great shape but just saying that if his alternator is good and hooked up properly with good connections that the truck should be able to idle indefinitely without stalling assuming he doesn't have everything under the sun running in he truck.

Regardless though the OP hasn't posted further info so we are just guessing. He didn't even state whether or not he jumped the truck to get it started.

---Aaron

 

Still should be plenty of juice to let the truck idle for as long as it wanted with a battery that is very low or discharged if the alt is good and connections are good.

I would seriously question the integrity of the alternator with these symptoms but the OP is saying he had it bench tested. I am taking him at his word. That only leaves the connections.

He can go ahead and replace both batteries but the fact remains that his charging system is not putting out enough juice to allow his truck to idle for more than 20 minutes before the batteries discharge completely and the truck stalls. That is not the symptom of a battery problem...it is a symptom of a charging system problem.

If we find out that he is actually JUMPING the truck to get it started then I would consider that he might have ONE bad battery in his dual battery system that is a problem. That is entirely possible.

Another thing could be that he was given the wrong alternator! If the guy at the parts counter gave him an undersized alt that could also be a cause.

My assumptions are as follows:

a) Alternator is good because the OP says it was tested
b) Alternator is the right size
c) Truck is starting on its own without a jump
d) OP is not turning on every possible load in his truck, has no big AC inverters running or other huge loads, or anything else running while idling other than maybe the headlights

If any of these assumptions are incorrect then it could be a number of other things, including just crap batteries.

I have beat this dead so absent any further info from the OP I have said all I can say and helped as much as I can. Just stating where I believe the most likely cause would lie based on the information we have. Garbage in garbage out as the saying goes!

---Aaron

 

Good grief watch for friendly fire!

I hope his truck hasn't eaten him or something. I'd sure like an update from the dude.

 

Some of you gasser guys may not know, that his truck doesn't turn the alternator on until the glow plugs have turned off. Up to two minutes that the truck has to run off nothing but batteries, WITH a heavy glow plug load.

If he hasn't already, he needs to get those batteries on a charger for at least 24 hours (48 is better) and then load test them. I'm betting at least one fails. And you want to replace them both at once. And test the alternator again, and hope you didn't blow it out with those bad batteries.

We also have to hope that all this low voltage screwing around hasn't fried the FICM, which is another reason it might not run.

 

In keeping it simple...there is one more item to check. Ensure that there is sufficient water in the battery. My 2003 x 7.3L gradually became more difficult to start, until it would not start at all. By gradually, I mean over two weeks or less. From the above posts, I determined that the batterys were low on charge. The windshield wipers would not work, with key on, and engine off. So I put the charger on, and checked the water in the batteries. I put in 1/2 gallon of distilled water (not sure that distilled water is necessary, but I heard it's a good idea) between the two batteries. Some of the battery holes were very dry. After adding water, and charging all day, the X started immediately. The autozone guys ran the system charging tests (i.e. battery, load charge, alternator, starter). Everything checked out OK. I am hoping that simply 'adding water' was a cheap, simple fix.

 

Looks like we managed to scare the OP away. Congratulations
Coming back to the issue, we assume some things not having precise data, but my thinking is, that when batteries start the diesel, they have to be pretty good to do that.
I had alternator failure in the mountains and I managed to drive 150 miles stopping at 3 places with restarting the engine before I found replacement. The batteries lasted just fine and I turned the AC and blower off.
So alternator good or bad, the truck dying in few minutes after start is draining the power at alarming rate.
Let the OP figure out the obvious problem before we flood him with speculations?

 

Read the whole thread before you pick one post and decide to make yourself look like a SMART GUY, ok Aaron, and BTW you are wrong