treystoys

As stated above, 89 f350, single tank, not running. Started as an intermittent no start issue, actually drove it to the shop. But is now not starting and has low fuel pressure, 9psi at the shrader. Has new high pressure pump, checked for supply to the new pump from in tank pump prior to changing. Stayed 9lbs at the rail both before and after hp pump install. Changed fuel filter after hp pump, even pulled line from filter to rail and blew it out to check for obstruction. Engine will run on starter fluid just fine. Is it possible the low pressure pump is not supplying enough pressure to the canister and the hp pump is cavitating somehow? I just ordered a bosch hp pump to replace the napa brand I installed a few days ago just in case. So here is what we've tried in order tried:

Checked fuel pressure 9psi key on or cranking, does not change.
Checked pumps for operation
Checked fuel supply to high pressure pump
New napa brand high pressure pump
New fuel filter
Jumped out relays on fender well
Blocked off return line to circumvent possible bad regulator and force fuel pressure..still 9psi
checked for wet plugs incase injector(s) stuck open. All plugs dry
tried external supply pump from gas can to hp pump.
Blew out fuel line from filter to rail...

At this point I've got a different hp pump on the way and I have a new in tank pump assembly to try as well but as I said the small supply tank pre hp pump is filling just fine. Only other thing would be a bad computer? but would that exibit low fuel pressure? Im open to suggestions. This is one of our shops trucks. I've tried to be as systematic as possible and had another mechanic look at it with me but we are all stumped. Not one to ask for help but I'm tired of looking at this thing.

Thanks guys!

Trey

treystoys

Not sure why this got posted to the late model forum, I posted this by asking a question through the pop up "ask a question" window and this is where it landed. If it can be moved please do so, and let me know what forum it goes too! Thanks

Trey