Hi, I am brand new to the forum so please excuse any mishaps I may have. I own a 1997 F250HD with just over 367k miles. My issue is recently whenever I go to start the truck in the morning, it will crank fine and run for maybe 3 seconds before quitting. If you try to crank again it will do nothing but almost start, I'm not sure if it would start during the second crank since after 10 seconds of the truck sputtering and almost starting did nothing. By the third crank it would start and run rough for about 10-15 seconds then clear up. I am a bit puzzled with this because I have found a way for the truck to start on the first try after playing with it for around a week. If I turn the key on and the a/c is on and running, I let it sit for about 5 seconds then turn it to the off position then I turn the key to the off position. Then I turn the key back on and after the wait to start light goes off I turn the a/c back from off to normal a/c setting and the truck cranks and runs with no issue at all. I can also smell heavy fumes in the cab after starting the truck like this. Before this issue occured, I recently put a adrenaline HPOP, new ipr, new icp, billet hpop reservior spacer, and oversized hpop lines on the truck due to a previous issue. Truck has a brand new PCM and year old Melling Lpop. Everything in the oil system is new except injectors. Any help would be greatly appreciated because I'm stumped.

 

What temp is it outside?
Are your GPs working?
Are the injectors originals?
mechanical fuel pump?
What pressure is it running?
Do you have full oil level in engine?
The AC thing could mean your ignition tumbler is shot. I know mine was and easy 20 dollar part to replace

 

Thank you for the insight! Ambient temperature was at least 70° outside each time, I live in Florida so never had cold start issues, just this new issue popped up months ago after I changed a bunch of parts. Pretty sure they are original injectors that were "remanufactured" can't say it for certain as I am trusting the person who sold the truck to me. Full engine oil level as it happened even right after a fresh oil change. Mechanical lift pump which seems to be putting out plenty of pressure when cranking, gauge was above 60psi when checking it before. I thought I may be losing prime so I pulled the filter cap off the next morning and it was full of fuel still so that doesn't seem to be an issue. Ignition tumbler huh? I'll have to look into that thank you!

 

I went out and started the truck today, ambient temp 80° with the a/c setting off as I have done before which didn't seem to help, but it cranked up first try. It fired up fine then nearly died twice and I heard a few squeals out from under my hood then the truck ran rough for about 30 seconds and cleared up.

 

Motorcraft sensors or Brand X? How old is that mech pump? 60psi was cranking or running?

With nearly 400k, you probably could use an ignition switch. Drop yours and see if it is loose, really easy.

 

All OEM Motorcraft sensors and filters. Not sure on the age of the pump but it is not the stock pump as I pulled the stock pump out of the toolbox when I went to clean the truck out. Only tested pressure while cranking, will try tomorrow while running to give proper measurements. I appreciate the suggestion as the ignition switch doesn't look the best.

 

under the hood are three relays, the PCM relay over time gets flakey
You can swap with one of the three to rule it out