Battery and electric questions.

[CivilEGR]

I've had trouble starting my 1008 the last few times and I'm trying to figure out what's going on. Today I tested both batteries after it wouldn't start and the back battery was 12.5 and the front 11.9. The way these batteries are set up, shouldn't they both read the same? Also, thinking about the front battery being low I checked for parasitic draw, but after checking between the negative terminal and negative cable on the front battery, I was getting only 3.5mA, which I guess is acceptable. Any thoughts on where my voltage is going after a few weeks of sitting? And followup, if my battery is just bad, do I need to match my battery cold cranking amps, or can they be different? Are the CCA addative the way the batteries are set up, or does it only turn on the lowest cranking amps?

 

[Mullaney]

I've had trouble starting my 1008 the last few times and I'm trying to figure out what's going on. Today I tested both batteries after it wouldn't start and the back battery was 12.5 and the front 11.9. The way these batteries are set up, shouldn't they both read the same? Also, thinking about the front battery being low I checked for parasitic draw, but after checking between the negative terminal and negative cable on the front battery, I was getting only 3.5mA, which I guess is acceptable. Any thoughts on where my voltage is going after a few weeks of sitting? And followup, if my battery is just bad, do I need to match my battery cold cranking amps, or can they be different? Are the CCA addative the way the batteries are set up, or does it only turn on the lowest cranking amps?

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It would benefit you and the truck to "rotate the batteries" maybe twice a year. I'm concerned that maybe you have a weak cell in the 11.9 battery. Might be worth taking them both out and go to your local Auto Zone, Pep Boys, or whatever parts house and have them load test your batteries. If you happen to have an Interstate Battery store close to you, they will (generally) have a more skilled workforce.

One weak battery will drag down the other...

 

[87cr250r]

Good batteries should hold 12.6 volts, even after a long period of time. If the battery dropped to 11.9 volts and you don't have a parasitic draw (these trucks don't in stock trim), then your battery is bad. Typical life expectancy for a lead acid battery is about 7 years. If you live in a hot environment such as Arizona that life can be as short as 3 years. The batteries are also subject to mechanical damage so if you drive on rough roads that can cause failures as well.

 

[Keith_J]

Stock CUCV charging system is two batteries in series, charged by two isolated negative alternators, also in series.
Only the starter is 24 volts, the glow plugs draw off both batteries with a large ballast resistor in series. This ballast resistor is on the firewall, shielded by a black metal plate.

Alternators only maintain charge and usually require 30 minutes to recharge fully after a start. All batteries benefit from periodic charge with a modern charger. Otherwise discharge degrades the electrodes.

As the start process places an equal load on both batteries, using identical batteries is beneficial. But if the vehicle has been modified to eliminate the glow plug ballast resistor, the front battery will be worked harder.

 

[cucvrus]

Check out the chart. You have a battery that is 40%. Also bypassing the glow plugs to the 12-volt power point on the firewall will put all the load on the front battery every time you engage the glow plugs. Keep that in mind. Everyone always refers people to the TM's and then advises to hack the system. The stock configuration works fine. Maintain what you have and correct what is causing the issue. Load testing the batteries is a good start and making sure the alternators are charging correctly is the next step. Good Luck.

 

[87cr250r]

The ONLY problem with the stock resistor system is that a bad glow plug causes the others to burn out as well. This is really minor as most replace their glow plugs as a set anyways.

 

[Keith_J]

Properly functioning and connected glow plug system senses voltage at the glow plugs and shuts off at 16.2 volts. Failure of one or more glow plugs will cause a reduction of pre glow time along with delayed start.

The voltage sense wire is the thin orange wire at the glow plug solenoid. Wiring diagram in the TM shows this incorrectly connected to the solenoid input, it must be on the output terminal with the large orange wires which are branched out to to the glow plugs.

I had 3 glow plugs burn out within a week. None swollen, all were original 33 year old and 33,000 miles. I noticed the third as pre glow was less than 2 seconds with engine at 70°F. None were swollen. If cascade failure were an issue, there would have been more than 3 failed.