1997 Ranger starts when cold, not when warm

My truck starts OK on the first start of the day, when the engine is cold. If I shut it down it won't start again (took me a couple times to figure it out).

It's been at the shop for almost 2 weeks, my mechanic is stumped. He's replaced the spark plugs and coils. Didn't fix it. Then he replaced the thermostat, still no go. He says he checked the fuel pump and it's OK.

Next step is to change out the computer for a rebuilt one, thinking that there is a problem concerning the temperature sensors or something, that tells the fuel injectors to open up? (This was my suggestion, given me by two other laymen).

HELP!!!!!!!!! He's been unable to come up with an answer, and I am without a vehicle. TIA

You need to go to a shop where they have a qualified service man. He costing you time and money.

rhandwor is right. Your mech is playing the guessing game. You may have a problem with your temperature sensor (not the gauge sensor) or your module could be out of whack.