hey guys, my 6.7 is being extremely weird. On a nice cool morning it will start up fine no noise no hesitation anything. As soon as it starts getting warm outside and I try to start it, it will sound like an air impact under the hood torqing my wheels. Some times it will start like that some times it won't.
Ive ran through 2 sets of brand new batteries (keeps killing them so maybe s constant draw?) I put a new starter in it, starter relay and nothing has changed, it throws a P0336 code on occasion but I think that's due to extended crank/no start?

When i have batteries fully charged 13v on charger An tuner it will start every time no matter what. Do I have a bad ground somewhere corroded wires? If so where would they be? Terminals and starter connections are all clean. What other connections do these cables go to?

Maybe check the alternator. Check the charge while the engine’s running; should be around 14.4 or so.

It charges at 13.9-14.4 at all times

it charges at 13.8-14.4

Check and see how the starter gear is mating to the flywheel teeth. I have seen where the mating was off-center causing the starter gear to rub. Most auto parts stores sell starter shims, which allow you to perfectly align the gears.

— Dave

thanks for the reply Dave,
ive already thought of that but direct sunlight could never cause enough heat for my flex plate or starter gear to expand/contract that much. Like stated above it only does it when it's hot. There is a voltage draw somewhere on the truck. And I'm hoping someone may know?