Failing to start
 

I have a 86 F150 that has a starting problem. It started approximately one year ago an has become more frequent. The truck when it starts will usually start within a few seconds of the starter engaging. Sometimes it takes 2-3 attempts before the engine starts. When the engine starts it runs fine. I have left the truck at work a couple times because it would not start. Returning to work for my next shift the truck starts. The only check I have made todate is to check for spark when it failed to start, which was present.A mechanic replaced the fuel tank switching solenoid when the vehicle left me stranded but as I suspected it did not fix the problem. I replaced a starting relay years ago but that problem prevented the starter from being energized. Outside temperature does not seem to have any effect on the starting.I have not been able to do much trouble shooting as the truck has not failed to start whenI park it at the house. The fuel filter has been changed once but since it runs Ok I have not replaced it again.