I have a 1988 F-150 with a 302 fuel injected, manual trans.
It has almost 200,000 miles on it of which I put about 10,000.
It runs great, doesn't burn or leak oil, and starts right up when cold.
My problem is that after running for ten minutes or so( the time it takes to get to the local Home Depot)it struggles to start. It cranks for at least 20 seconds and finally,  slowly, wheezes to life.
I've changed the plugs, distributer cap and rotor, and plug wires as a routine tune-up.
The MAP sensor has recently been changed and I just changed the ignition module at the advice of a friend that had the same problem.
I've had this truck for about a year and a half and this has been the only major problem.
Any ideas of what it could be?
Thanks.

I am assuming from your post that the vehicle is cranking at normal speed when the problem occurs. If that's the case then you might try holding the throttle to the floor to see if it starts sooner (please release throttle as soon as vehicle starts bg). If this helps, then you may want to check the coolant temp sensor. When the sensor goes bad or looses connection at the harness, the computer then assumes a coolant temp of minus 40 degrees causing a rich condition.
  There are also other things that can cause a long crank time (such as a leaking or stuck fuel pressure regulator), but the coolant sensor is a good (common) place to start.
   Good Luck,
                        Tim's Tech Service
   
                   

Thanks for the suggestion Tim.
I'll change the temp sensor and let you know how I made out.
electromotive1

Hey Tim,
Just want to thank you and let you know that your diagnostic of the warm engine start problem of my '88 F-150 was dead on.
I changed the coolant temp. sensor as you suggested, and it not only starts every time, but also runs much better overall. Idle is absolutely perfect now, doesn't surge up or down by more than 100rpm(800-900).
Thanks again
electromotive1

Your very welcome,
 Tim