I just installed a new set of F1 Mach1 injectors this evening. I ran the truck about 5 miles..truck ran fine. When I got back home I noticed a hissing noise from my fuel cap. I unscrewed the cap and it blew off with what seemed to be 30-40 pounds of pressure. Reinstalled the cap and ran the truck again...pressure built up again. Didn't do this before the injector swap. Any Ideas???? Thanks...

2001 HO 6-speed

 

It sounds like the injectors are not sealed to the head and compression is whats building pressure in the fuel system. You will need to pull all the injectors asap and inspect before you hurt something. you may have a missing copper washer.

 

I just pulled the F1 Mach 1's and reinstalled the Pensacola Diesel injectors I originally had in. Pressure in fuel tank gone. I didn't see any missing washers or other issues. To get pressure back into the fuel tank, the injector(s) would have to be leaking compression back through the injector, A missing washer would blow compression back into the head/crankcase and cause excessive blowby.

2001 HO

 

No....a missing copper washer lets compression into the fuel return well that returns to the tank. To get to the crankcase, it would have to get past the copper washer and the nitrile o-ring above it.

 

Also if the connector tube nut is loose the IP pressure (2000+) will leak around the point where the connector tube meets the injector, this fuel and pressure are vented back to the tank via the fuel return passage that is in the head, same thing will happen if the copper O ring is missing/damaged or the injector hold downs are loose.