Fuel pressure Mercury Pro Max 225

[jdewaard]

I have 35 psi fuel pressure on my 2000 Mercury Pro Max 225 at idle. Isn't this supposed to be 39 psi? Will 4 psi make a difference in power or top end rpm's? Everything is clean. All new filters. VST serviced. Injectors serviced. Could this be a bad regulator (weak spring inside regulator)?Thanks

[myron]

or it could be your gauge, I would think it is OK, unless you are having issuses

[dagodiver]

What is it with key on not running. ie no vacuum signal.
Vacuum signal should pull it down a few.

Dago

[wired247]

At idle you have low manifold pressure ( high vacuum). It causes the regulator to drop fuel pressure to 35-36 because of the vacuum line attached to it from the manifold. At low vacuum like WOT and just plain not running the fuel pressure increases to 39.

[jdewaard]

The fuel pressure is 35 psi with the key on, not running. After the pump stops running and I turn the key off it drops to 31 - 32 psi before holding. I am thinking the regulator has a weak spring (age). Any opinions?

[Go Time]

Early model Promaxes have 36-39# regulators. The later model (after serial number OG303xxx...1996 or newer) Promaxes usee a 35 +_1 regulator....you're probably fine.