General question about diesel engine electrics

[bshupe]

Ok, so I am in pursuit of a battery drain in my system and while this post is not specifically about that problem my troubleshooting process raised a question for me. I am new to diesel so please dont flame me if this is a total noob question.

All of my previous automotive experience has been with gas engines. When you had a situation where your battery was not holding a charge the fastest, easiest way to see if the alt was bad or not was to start the car and then disconnect the battery. If you turn everything in the car on and it all worked you were pretty safe in saying the alt is fine.

I tried this with my CUCV and after a short but noticeable pause, the engine died and all lights etc turned off after removing the neg cable. I had expected the engine to keep running and the lights etc. to either stay on or go off or weak (based on my gasser experience)

Is there something different about diesel engines or CUCVs that would cause this result after removing the battery cable? Or, did I actually confirm that my drivers side alt is completely dead and thats why the engine and everything died after disconnecting the battery. If the alt is dead then how is it keeping running with the cable connected? Is the passenger side/rear battery alt backfeeding the front battery through the rear and so this is keeping it driving with one bad alt?

What is it that turns off a diesel in the first place since it has no electric ignition and a mechanical fuel pump? Im embarrassed to ask this but I just need to know.

I realize there are a lot of questions wrapped up in this little post, I thank in advance anyone who takes time to sort it out and post an answer to any of it.

Thanks!

 

[GHall]

As far as the charging system goes, a volt meter would answer some questions.

 

[porkysplace]

It has a electric solonoid on the injector pump , if you pull the pink wire on the IP it will die also. Plus pulling the battery cable is a good way to fry altenators .

 

[MarcusOReallyus]

All of my previous automotive experience has been with gas engines. When you had a situation where your battery was not holding a charge the fastest, easiest way to see if the alt was bad or not was to start the car and then disconnect the battery.

That is a VERY bad idea.


You can fry an alternator that way.

 

[porkysplace]

That is a VERY bad idea.


You can fry an alternator that way.

It will also fry computers on newer vehicles .

 

[MarcusOReallyus]

Yep!

 

[bshupe]

OK, so its a bad idea. The question still stands though. Should the engine die when the battery cable is disconnected or should it continue to run on the power supplied by the alternator(s)?

 

[diesel583]

It should not run. Alternators have to have DC voltage to make AC voltage which is then changed to DC voltage to charge the batteries. When you unhook the battreies that all stops and usually destroies the altrenator diodes. That said the solinoid in the injection pump that lets fuel to the engine has to have 12 volts to open. You can run for sometime on batteries without the altrnators working but you have to have 12 volts to run.

 

[bshupe]

Thanks for the answer diesel583. In your (or anyones) opinion, how many start cycles do think the truck could sustain from fully charged batteries if the charging system is non-op?

In my situation, I can trickle charge my batteries and starting it 2-3 times per day I go about a week or a little longer before I get to low/dead batteries. I had been thinking that my charging was intermittent because my volt gauge shows in the green but maybe it has been giving me battery condition all along and not charging status. If this is the case then either both alts have failed entirely or, there is something the charging control logic that has failed and is not turning the alts "on" with the ignition. I have the schematics and have only started to dig in and see if I can locate such a control or perhaps a fuse/fuseable link that has the capability of taking out the whole charging system.

Thanks again for your time and input.

 

[GHall]

Have you had the batteries tested?

 

[bshupe]

They are both brand new. When this first started happening I had the original 6Ts tested and the front one was bad. I couldnt swing the cost of replacements so I swapped them both for standard size batteries.

 

[porkysplace]

What kind of shape are your battery cables in ? If they have corroded inside the insulation it will cause problems.

 

[bshupe]

Cables look excellent on the outside. If I peep on the copper elements inside the insulation at the terminal they have a touch of green on them but not bad at all.

 

[diesel583]

You could go for a long time with no lights or heater, just starting it a couple of times a day. The problem is the front battery will run down first and cause more problems. Could shorten the life of the starter. It would be way cheaper to fix it so it works like it was intended.

 

[bshupe]

Thanks - Im not planning to limp by recharging the battery once a week forever. Im just not the type to throw parts at it until the problem goes away. I want to learn and understand how the SYSTEM works so that I can find the part that is causing a SYSTEM failure.

I have also been putting my multimeter across the battery terminals when I percieve a change has ocurred either by how things are functioning and/or by the data the volt gauge is providing and I have found that I can detect when it is not charging. When everything seems good I have 14.8v on each battery. When things dont seem right I have high 12v to mid 13v on the front battery and 14.8 to the rear battery. This is pointing me to the drivers alt but I am still trying to narrow down if it is an input/control problem or a device problem. I am inclined at this point to rebuild the alt so I have ordered all the parts from CUCVElectric.com (2 full sets and 2 partial sets) so i can do that project soon.

I still am searching out the whole circuit to see if there is something causing the alt to not charge or if the alt is in fact bad or in the process of dying.

Is it possible for an alt to charge while the engine is running and then be a parasitic load while the engine is not running?

 

[MarcusOReallyus]

Thanks - Im not planning to limp by recharging the battery once a week forever. Im just not the type to throw parts at it until the problem goes away. I want to learn and understand how the SYSTEM works so that I can find the part that is causing a SYSTEM failure.

Bless you, my child!


Too many just start guessing, throwing parts at a problem. You can tell who they are because they never ask how things work, they just ask, "Could it be THIS? Could it be THAT? Should I rebuild/replace THIS or THAT?"

I still am searching out the whole circuit to see if there is something causing the alt to not charge or if the alt is in fact bad or in the process of dying.

Is it possible for an alt to charge while the engine is running and then be a parasitic load while the engine is not running?

Yes, that can happen.

 

[porkysplace]

A bad diode in the altenator will allow it drain the battery.

 

[bshupe]

A bad diode in the altenator will allow it drain the battery.

If it had a bad diode would it also charge (intermittently)?

 

[bshupe]

I have been studying the TM for the charging circuits and I have a couple of questions:

1. At the bottom/middle there is a diode. Because it shows wiring passing through the firewall harness plug it would seem that this is an external component to the alts. Is that true or is this a representation of the internal diode? Just by the logic of the circuit it would seem that the "exciter" circuit for the alts. is controlled by this diode and thus would be critical to its function.
a. If external, could it cause gen 1 to not charge?
b. If it can disrupt charging, where is the little guy physically on the truck and where do I get a replacement?
2. There is a relay "GENERATOR #2 RELAY" noted on the schematic on the right side just above the mid point.
a. The schematic shows no control circuitry for this. I would presume it is controlled by the ignition. Correct/incorrect?
i. Or, is the plug looking icon below it the wiring?
ii. If so, where do I find "Figure F-4" for the continuation of the circuit?
b. Could this relay affect the ability of the circuit to charge the battery(ies)?
c. If so, where is this relay physically and, where do I get a new one if its bad?
d. If there is a relay for GEN 1, is there a relay for GEN 2 that is noted somewhere else?
i. If there is no GEN 2 relay, why? What does it do for GEN 2 that GEN 1 does not need?

Thanks for your help!

 

[scottladdy]

Diagnosing Charging and Discharging issues ...

Thanks - Im not planning to limp by recharging the battery once a week forever. Im just not the type to throw parts at it until the problem goes away. I want to learn and understand how the SYSTEM works so that I can find the part that is causing a SYSTEM failure.

Good idea. Another consideration is that you are likely reducing the life of the battery in question significantly. You'll have to perform the cost/benefit analysis on this for yourself. If you really want to learn the electrical system in these trucks, it may well be worth the cost of a battery .

I have also been putting my multimeter across the battery terminals when I percieve a change has ocurred either by how things are functioning and/or by the data the volt gauge is providing and I have found that I can detect when it is not charging. When everything seems good I have 14.8v on each battery. When things dont seem right I have high 12v to mid 13v on the front battery and 14.8 to the rear battery. This is pointing me to the drivers alt but I am still trying to narrow down if it is an input/control problem or a device problem. I am inclined at this point to rebuild the alt so I have ordered all the parts from CUCVElectric.com (2 full sets and 2 partial sets) so i can do that project soon.

Drivers side alt "system" is failing intermittently.

Sorry to say that, because intermittent problems can be the toughest issues to diagnose, as sometimes you just have to "wait" for the failure conditions to occur. Still, a systematic diagnosis starting from the most likely "common" failure point working backwards, eliminating circuit branches as you go is recommended. Keep track of your testing by printing off the schematics and marking off the results of your tests.

Try simple things first. e.g. is the 2 wire plug on the alternator providing a solid connection? Use the troubleshooting processes documented in the TM's. Just consider the varying skill levels that the TM's were intended for. They are very well thought out in general.

I still am searching out the whole circuit to see if there is something causing the alt to not charge or if the alt is in fact bad or in the process of dying.

I strongly recommend taking the alternator to a shop and getting it bench tested. It will be a formal diagnosis. There are a number of places that offer this service "free" as a loss leader. 1) They get you in the store. 2) They build favor with customers. 3) They are likely to sell you something, as even if the alternator is good, you'll "remember" something you wanted to buy anyway. 4) etc.

I advocate rebuilding the alt with the CUCVElectric parts you have on order. But getting the alts tested will provide you with the knowledge that you desire as to whether or not there is an issue in the alts before you rebuild them.

Is it possible for an alt to charge while the engine is running and then be a parasitic load while the engine is not running?

Technically, the alternators always have a parasitic draw on the system. In a properly functioning alternator, the diodes are usually very effective at reducing this draw to what is normally negligible for a vehicle with a healthy battery for even months at times. But, to answer your question, yes, it is possible.

You need to formally diagnose the draw.

I would treat the intermittent charging issue as a separate issue from the concern you have over the apparent battery discharge. Diagnose each separately until you find that there is a common failure point, if any. I believe it has already been recommended that you check the system for a parasitic draw. If there is a draw, find and fix it. If there is no draw, well then your battery may be on it's way out. Get the battery tested.

As I said above, your testing results are indicating to me that your front battery charging system is intermittently failing. Focus there.

Keep it simple. While eletrical systems can appear overwhelming, they are overall nothing more than pathways from one pole to another. Look at each pathway one step at a time. Test each branch and eliminate those that test OK. Keep track of your progress using the schematics as a visual aid.

I hope this helps ...