Grit Dog

Truck has 115k mi. Bone stock except Bullydog.
Spends most nights in the shop plugged in but recently if it is out in 0 deg or below weather and not plugged in it will take several tries cranking before it lights up. -20 a few weeks ago outside overnight not plugged in, no start at all until towed in and warmed up..
Batteries are excellent condition, good connections, matched agm Odyssey batteries, grid heater works, lift pump works, not gelled up. Not making oil (fuel in oil). Runs great. No white smoke on startup warm or cold.
Fuel mileage is down to about 14mpg but ak winter fuel, 4wd all the time, some idling seems about right.
Not sure of LP pressure but it runs to prime with key on. Fills the filter bowl in 1-2 sec.
Have noticed slightly longer cranking time with lower temps but not more than 2 sec or so unless left out in the cold and completely cooled down.
Running 15-40 Dino oil but switching out to 5-40 syn just because.
It doesn't just need plugged in. Used to start no problem if it had to sit out in below zero temps.
Have read a bunch but no particular solution unless the LP is weak or the injectors return rates are high not building enough rail pressure when really cold?
Help or suggestions please.

motrapper

Ok same truck as mine
Change the fuel filter or filters I have stock filter with the Fleetgaurd and the GDP big line kit and Cat 1R 0750 2 mic before the cp3
At 10 below last week it starts like its 80 outside without being plugged in.
Odds are its a fuel filter problem starting to plug problem ie needs changed or need to drain the water off of the stock filter.

Grit Dog

Thanks motrapper. No addl filtration on mine. Few weeks ago when it wouldn't start at -20 I replaced a 1000 mi filter that showed no signs of restriction, so the filter now is essentially new.
Update. I changed the oil to 5-40 syn and it spins over easier.
At 5 deg it started with less than 2 sec cranking. This morning after overnight of -5 deg it fired up as well. Cranked maybe 3 sec on the initial start.
The lighter oil has helped the issue significantly.
It's been a few years since I've had the truck in real cold temps and don't remember how long it cranked before when out in the cold.
Does this seem right?
Still a little uneasy about cold weather perf and it is warming some now so no chance to ck it at colder temps for a while.

Lary Ellis (Top)

I believe the ECM monitors the rpm at start and will not allow it to fire off if it is under a certain threshold...the thinner oil in those low temps allows it to spin quicker and build compression faster which is probably why it starts better now

Grit Dog

Makes sense but it still spun pretty quick even when it didn't start. Quicker than I've heard some 3rd gens with weak batteries.
Started fine sitting out on the hill all weekend but it was warm +10 or warmer.
Weird though it threw a ck engine light but my Bullydog says no dtc codes?
Tried the key trick and all that did was some sort of self check on the guages and idiot lights and it displayed a couple numbers that did not correspond to dtc codes.
Gonna stop and put a scanner on it from the parts store. After 15 or more key cycles it hasn't cleared.

Grit Dog

Just to update it was the injectors. 2 of them were getting weak. Hard starts got worse.
Put new ones in it last month now it starts immediately regardless of the temp.