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Recently on our 91 6bt it has started having an issue with fuel pressure bleeding down on shutdown. This only happens occasionally. Crack the injectors, bleed them and everything is fine for a while. No pattern has been noticed.

What kind of issues would cause this?
 

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Two common problems to check:
Dirt in the fuel tank has worked its way into the lift pump and is keeping the check valve in the pump open permitting the line to drain back into the tank.
Or the fuel line has a rust perforation between the tank and lift pump (usually in the area between the tank and frame rail) or a rubber hose has gone bad in this same line.
 

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fuel pressure

It maybe the mecanical lift pump, the diaphram went out on my 4bt pump and everytime i started it and shut it down i would have to crack the injectors and bleed the system out, and it also allowed fuel to enter the crank case and raised my oil level!
 
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