MS3 and Returnless Fuel Systems

[Healey3000]

Hi,

Searching through the forum, it appears that MS3 can support PWM returnless systems. Why does the MegaManual (the pdf version) say that a return type system is the "recommended" installation? is there a weakness with MS3 in this regard?

I'm also a unsure whether the Ford FPDM handles the PID control algorithm in response to a command PWM from the ECU or whether the ECU handles all the computations for closed-loop control. What are the current "best practices" for a returnless system? A recommendation on specific hardware would be most appreciated.

I've read about the possibility of vapor lock problems with returnless systems. This car does not have a cross-flow head so the fuel rail is sitting close to the exhaust manifold. I could perhaps add some heat shields or insulation but am I asking for trouble?

Thanks.

[dontz125]

As you noted, a major issue is fuel heating. A return system dumps the heated fuel back into the tank and draws cool gasoline to pump up to the rail. A returnless system can work just fine if you take the potential problems into account.

The other issue - especially with boosted systems - is maintaining a constant pressure differential across the injectors. A manifold-referenced regulator with a return line can keep a steady 43.5 psid all day long with a simple always-on fuel pump. A returnless system either has to use a single-port fuel rail pressure sensor (AEM or other type) and accept a wildly varying dP from idle / overrun up to full boost, or requires a referenced (Bosch / Ford 2-port) sensor. Note that one of the 'Pressure Sensor' options for the MS3 is a differential sensor; as the 2-port returns a differential value, you can set your desired value to 300 kPa and just leave it.

For those with heating issues or amp supply issues (*cough* bikes *cough*), the two methods can be combined - set the dP sensor to ~ 50psid, and the regulator to 43.5 psid. The PWM controller (MS3 or standalone) will modulate the pump according to demand, and the regulator (and return line) will ensure there is a fresh supply of cool fuel at the rail.

[Healey3000]

Hi,

I plan on using a manifold-referenced FPR, and this engine is normally aspirated. I like the idea of a returnless system in part because it reduces the vapor control requirements. Running a single line is also attractive as are the electrical and thermal efficiencies. I'll have to pay attention to insulating the fuel rail.

The important question - is MS3 fully up to the task of handling fuel pressure control?