Performance Overflow Valve - PeachParts Mercedes-Benz Forum

mach4 · #11 01-08-2016, 01:18 PM

As one of the very few people that continuously monitor my fuel pressure in real time, I can report that fuel pressure varies significantly. In order to get a stable reading I employ three strategies - first I have a snubber consisting of a tiny orifice in an epoxy plug in the fuel transducer capillary line, then I have a damper consisting of a piece of closed cell foam ahead of the sensor, and finally I do software averaging of a significant number of readings. When originally installed, the readings were "reasonable", but after doing the spring stretch procedure in the OFV valve the readings jumped - not quite double.

So, while I'm not using the Performance Overflow Valve, it's pretty obvious that this mod would have a profound effect on fuel pressures compared to a worn spring.

The pressures are so variable because of the lift pump being a positive displacement design - when the piston is on the "intake" stroke pressure quickly drops to near zero and when it is pumping it jumps quickly to the limit pressure of the OFV valve or possibly a bit more. What I've been wondering about recently is the notion of adding a fuel pulse damper (pressure damper or accumulator) to the system between the pump and the injector pump. If it's true that the extra pressure of the Performance Overflow Valve increases performance by increasing the fill rate of the elements, it would seem reasonable to assume that a constant design pressure would serve the same purpose and possibly reduce the stress on the lift pump.

As I'm writing this, I'm wondering whether it's possible that a check valve in my lift pump might be leaking producing the low pressures I'm seeing i.e. allowing the fuel to bleed back through the pump rather than being maintained on the pressure side.