I have been having some starting problems with my truck. (F250/390). If it doesn't pop off within the first 5 - 10 seconds, the battery seems to not have enough juice to keep cranking.

I had the battery tested and it was charged and tested "OK" at the store. It is the largest one that will fit with 825CCA. I replaced the starter some time ago because it wasn't engaging. While doing so, I also added new cables from the battery and to the starter. The only thing I haven't replaced is the Starter Relay Solenoid. In that the starter goes to the solenoid, could that be bad and causing it to seem like the battery is too low to crank?

It seems like if I don't get it fired up right away after some cranking, I will be stranded (Haven't had it yet)! I thought it was the battery, but the lights are always bright but starting it seems to just about kill the thing every time if it doesn't start right up.

Any ideas?

 

Your last sentence indicates that the lights dim badly because the battery voltage is dragged down by starter current. If the battery has been load-tested and is okay, my vote is that you have partial shorts in the starter.
Semper Fi

 

Have headers?

If so, without a racing blanket, the starter gets cooked....

Leaks around the valve covers?

If so, the starter can get filled with oil over time, causing failure....

 

You can replace the relay and see if that solves it , there not expensive . Mine goes out every year or so . Another good idea is to ground the block to the frame , ground the alternator and voltage regulator as well . My mechanic friend told me ford trucks didn't ground the alt and volt reg very well . So I did and I havent had to replace my alternator ever since . I am running ground from batt to engine block then ground from block to frame . Then ground from alternator to voltage reg to batt neg . Never can over ground these trucks . Made a huge difference in the last two years . Also might want to replace voltage reg too . Good luck .

 

i have a battery that tests good, and holds a charge. But doesn't have the power to start much of anything. I don't know if you are experiencing the same thing?
If you can get your hands on a spare battery, you might try swapping that in and see if you still have similar problems.

 

Batteries get old and tired. They still hold a charge and give 12.6v at the terminals. The key is a load test. The shop should put a 100 amp load and the battery should supply it for 15 seconds according to the manual.
If you have a battery that is five or more years old, toss it. Why wait for headaches to save a few bucks?