Fuel Pressure: Merc 500EFI & 525EFI
 

What fuel pressure is the 502cu.in./500 hp EFI Merc motor running? How much fuel pressure is the 525 hp running? Are the injectors the same size on these motors?

The fuel pressure for the engines with MEFI 3, 8.2L/HP500EFI [mpi, cool fuel, mercruiser MPI intake manifold is [43]psi And it lookes like to me the 525 will be the same psi becouse the regulator has the same part number and [43] psi reading after it as the 500 EFI, But the Injectors have too different part numbers between the too, So they should not be the same. The 500 HP, Injector part # is 849896 and the 525-EFI is #805225A1, And the regulator part # for both is 861126A1. Hope this helps you out some. PS [43]psi is with the vacuum hose pulled off, If left on it will read any where from 4-6 psi lower, And would read around 38psi.

Some 500EFI's were 38lbs with 38lb injectors, thats what mine was, and its a 2000

my 2000 502mpi reads 36 psi, is that too low?

As long as that reading is with the vacuum hose hooked up you should be with in specs, The [1-2]psi might be just the gauge is off a little, Is the gauge mounted on the dash? It could just beouse of a longer hose giving a off reading is all. From what I could tell and remember the only fuel system that has a [36]psi fuel regulator was in around 1996 when merc was running the MEFI 1 ECM on some engine "not all" with spechial fuel injectors named [Keihin] And those too engines where the 7.4L [454] and the 8.2L MPI [502]

it is with vacum hoses hooked up and the hand held guage hooked up the the shrader valve. The pump/regulator and all hoses are new, it does go up to about 40 on takeoff then settles at 36

(best I can tell when I ooked back at it on the rear bench when running)