Weird no start

[BoeingDiesel]

I recently read that Ford has thousands of vehicles that can't complete the build stemming from the back order on CPU's which will probably drive up the used resale market.

 

[Tractorat]

Sounds like a lot of work to me. Now I dont know what Im talking about. But if you just try to jump start the truck, wont that tell you that maybe the batts are not performing ?

 

[petersonj]

But if you just try to jump start the truck, wont that tell you that maybe the batts are not performing ?

Not necessarily. If the problem is in fact a poor electrical connection, jump starting the truck could bypass or include the poor electrical connection, thus resulting in an incorrect conclusion.

The voltage drop test I described is actually a very simple and a very accurate test - it just takes a lot of words to describe how to do it.

Unfortunately, the voltage drop test is rarely used because the test itself is one of the most misunderstood tests, which is rather ironic because it is one of the simplest and most accurate methods of testing high amperage circuits.

- John

 

[brucejohnson]

Ohm's Law:
E-IR
I=E/R
R=E/I
If you take the voltage reading across a resistance (in this case the internal resistance of the battery) you will read the voltage across the six battery cells (~2.1vdc per cell). By connecting the remainder of the starter circuit when you activate the starter switch you will read a voltage which is now split with the circuit's other resistance drops across the wiring, starter motor coils, and any other circuit that remains active during the start cycle. If there is insufficient current flow due to excess resistance like corroded or loose connections, bad wiring, sulfated battery cell(s), etc., then you will not be able to start the engine as well as not enough current/voltage to illuminate/activate any lights or additional circuits, etc.. The voltage test John and David suggested makes it a quick and easy test if you don't have a load tester or carbon pile.
The one bad battery may draw the voltage/current down enough to cause issues, even it the other battery is good. I have not tried to start with only one battery, but have heard of others just using one to start their vehicles. Maybe you could remove the low reading battery as a test to see if the good one makes a "little stronger" attempt to start the engine. At 12.1 vdc that battery is only ~50% charged.

 

[BoeingDiesel]

I had the batteries load tested etc. and both came in good. After further inspection, the battery harness is in serious need of replacement so I ordered the Genos' harness set last Sunday and Genos shipped on Monday. Fedex tracking showed it was scheduled for delivery last night by 2100 but it didn't happen. I checked the tracking this morning and now it says the package is still in Braselton GA. with no scheduled delivery date. WT? and of course Genos' is closed on the weekend so I'll have to wait until Monday to see what is going on with this. The truck doesn't have to roll but still like to get this done and over with.

 

[Vaughn MacKenzie]

BoeingDiesel when I had a similar issue with my truck it turned out one of my battery cables was bad. Lights shone brightly and everything worked 'til I hit the starter then nothing. The cable could carry some current, causing everything like the headlights and wipers to function normally, but it was not capable of carrying the massive current the starter requires.

 

[BoeingDiesel]

The new battery harness came in Tuesday and I'll install this weekend. After further inspection it became very obvious the original harness was in bad shape and I'm kind of surprised that I didn't address this sooner. The Genos harness, (Custom battery Cables) is high quality and most likely the last harness this truck will need.
Thanks all for your insight, I really appreciate it.