OFV (Whole) rebuilt with mod'd spring - Page 2 - PeachParts Mercedes-Benz Forum

Diseasel300 · #16 06-13-2018, 10:57 PM

Prior to the 60x series engines, the overflow valve contained a ball bearing acted on by a stiff spring. The spring tension served to regulate pressure in the fuel rack and to force the ball against its seat when the engine stopped to act as a check valve, preventing drainback.

The 60x series and later engines use a drilled orifice in the OFV to regulate pressure. The check valve is now a plastic piece acted on by a relatively weak spring, the spring does nothing to regulate pressure it is only there to close the check valve. Because there is no spring tension in the check valve, the lift pump (which moves a higher volume in the 60x) can be used to prime the injection pump without resorting to using a primer handle like the 61x did. The consequence of using the 61x style OFV in a 60x is that you lose the rapid self-priming action. It will still prime itself, it just takes longer. Make sure the battery is charged when changing the secondary fuel filter and when you first install the OFV, it'll take a few cranking tries to burp the air out.

Once burped, the 61x style OFV works fine. I have one installed on my car because I had problems with the OEM one leaking down (warped and broken plastic is not uncommon) and the 61x style that Mark sells was roughly the same cost as the OEM one, but without the plastic piece to fail.

CrazyJew89 · #17 06-13-2018, 11:11 PM

Thanks for the thorough explanation. The only thing that doesn't make much sense to me is using an orifice to control the pressure. Using a fixed orifice would give a varying fuel pressure over the varying pump speeds, right? Potentially less pumping loses at low speed, but possibly a pain in the butt from a tuning perspective.

Did you notice any increase in performance from the elements filling faster like the 61X guys have?

Diseasel300 · #18 06-13-2018, 11:51 PM

The fixed orifice is a sound design choice, the delivery rate of the lift pump is far in excess of what the fuel rack needs, the fuel pressure in the rack remains relatively constant. I don't run a tuned pump or have an ALDA delete so I don't notice a huge difference. Getting rolling does have a noticeable improvement, but after that I can't tell a big difference from the seat of my pants. Since the 60x engines regulate fuel pressure by orifice size instead of spring tension, I wouldn't expect a massive improvement like the 61x would when running a worn out OFV with a weak spring. I chose the OFV for operational reasons, not performance.