Fuel Pressure In fuel rail.
Thread Starter
Junior Member
Joined: Aug 2004
Posts: 41
Likes: 3
From: Richmond, BC, CA
1990 560 SEL , 1998 S 420
Fuel Pressure In fuel rail.
1998 W140 M119 engine. What does the manual says the fuel pressure in fuel rail should be? My fuel regulator gone bad and I replace it with a new one. With a calibrated fuel gauge, and vacuum hose disconnected, I got 50 psi! I was expecting it to be 55 psi. Could someone please shed some light. Thanks you!
Thread Starter
Junior Member
Joined: Aug 2004
Posts: 41
Likes: 3
From: Richmond, BC, CA
1990 560 SEL , 1998 S 420
Wow! running at 60 psi? Did you mod your fuel regulator (FR) into a manual dialing? The FR suppose to maintain the fuel pressure in the rail no matter what the demand of the engine! The volume can varies in relation to the engine demand, not the pressure. That's is what I thought? Your less restrictive fuel filter does help to eased the flow of volume. Pressure in the fuel rail should remained the same. 
I should also mention here that with the vacuum hose attached, it will only reduce the fuel rail pressure, momentarily in relation to the vacuum. Thus, at idle, strong vacuum, lower psi. But always "trying" to reach its (FR) set pressure. Yes, the fuel rail pressure thus varies, to the lower end and never over the set pressure of FR.
Oldsinner111, thanks for the info. Anyone has this info from the manual, please chime in. Thank You!
I should also mention here that with the vacuum hose attached, it will only reduce the fuel rail pressure, momentarily in relation to the vacuum. Thus, at idle, strong vacuum, lower psi. But always "trying" to reach its (FR) set pressure. Yes, the fuel rail pressure thus varies, to the lower end and never over the set pressure of FR.Oldsinner111, thanks for the info. Anyone has this info from the manual, please chime in. Thank You!
