Hi,

1989 F250, 4.9, 5 speed, well north of 300,000 miles. Truck is extremely hard to get started. Spark is good. thought I got some bad gas so ran some out of the line. Truck started but once in awhile would miss at speed. Put Heet in tank and tried again but no start. hooked up fuel pressure gauge and got 0 psi. Changed fuel filter. When draining old filter it was very dirty looking. Primed lines by cycling several times. gauge will now go to 72 psi. When cranking it falls off fairly quickly and if I kept cranking it would go all the way to zero in about 10 seconds. I am thinking the rear pump is not keeping up with demand?

 

72 PSI is too high, should not be over 60 PSI.
Sounds like a bad distributor also (no PIP to keep the pumps going while cranking).