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Fuel pressure

i have a 88 ford f-150 5.0 with the key on i get 40 psi start the truck i get 35 psi all within specs,but when i rev the engine it drops to 20 to 25 psi then gose back to 35 psi. is that normal and if not what could be the problem? thanks

The problem might be with the fuel pressure regulator. With the engine idling, pull the vacuum hose off the fuel pressure regulator. The fuel pressure should increase. If it doesn’t, the fuel pressure regulator is malfunctioning.


has a new fuel pressure reulator but i did pull the vacume line off and it increased 10 psi

Your fuel filter is clogged or the fuel pump is weak.