[Chris90F250Diesel4x4]

My 1990 F250 starts right up first thing in the morning but runs really rough for the first minute.
If I can keep it running for the first minute it starts and runs fine the rest of the day.
If it stalls during that first minute then I have to push on the air bleed valve by the fuel filter while cranking the engine for a couple of minutes before it will start, then fine after that.
It is fine after sitting during the day. Only happens first thing in the morning after sitting over night.
I found a loose fuel line connector where the input goes into the high pressure pump. I tightened that 3 days ago and still the same problem.
I can't see any other places where there is a fuel leak including the return lines which someone suggested checking.
How do I find the place where air is getting in over night? Can I spray carb cleaner around the engine while it is running like a would with a gas engine or does that not work for diesels?

 

[Bill1013]

Since you messed with the hard line from filter to IP it probably disturbed the seal at the filter, those seals are known as "Olives", they are 5/16" ID, they get hard and will let air leak in but not fuel out. The "Olive" at the filter from lift pump is 3/8" ID. There very hard to dig out of the line nut, use a dental pick to do it. Most any Hydraulic shop will have them, or stack a couple of O'rings in place of them.
Hardware stores have O'rings, use only Viton. Harbor Freight has a cheap set of Viton rings, handy to have.

 

[Chris90F250Diesel4x4]

Thanks Bill !