Running dual Fuel regs?

[spf_lexus]

I noticed today my car was running much better after swapping a walbro for my stock fuel pump, which is a 190lph, not the 255. It's small but larger than stock so I know it can flow more, and it's not 18 years old! I noticed that the car is less jumpy at low vacuum, an area it used to buck and miss. It is still doing it but is tamed down... so I'm guessing I have a fuel pressure issue? The misses come when i'm usually climbing a hill or want heavier throttle in a particular gear, where the ECU would add fuel to the opening throttle plate. I have my oem fuel reg (mounted on rail) still hooked up to a vacuum source and my Rising Rate FMU in return line, BOTH ARE OPERATING. Should I just unhook the stock one and run the FMU alone? It has base fuel setting and boost onset setting. Could the stock regular possibly be counter productive with the FMU? And could I crank up the base pressure to accommodate the low vacuum situation?

 

[Zuffen]

If you run 2 FMU's one will always have a higher release pressure than the other.

If the factory unit dumps fuel down the return line at (say) 43psi and the aftermarket unit at (say) 50psi which one will open first?

You're right (you get the prize) the factory unit. The aftermarket FMU will sit ther looking cool and doing zilch.

I'd remove one or the other, personally on an unmodified engine I'd leave the factory unit and on a modified engine hang onto the aftermarket unit.

2 FMU's are only adding complication and doing nothing for performance.

 

[spf_lexus]

Thanks Zuffen

What would happen if I just capped off the OEM regulator and slightly raised my FMU? After all, both are mounted on the same fuel return. If anything would it run a little on the rich side?

 

[Zuffen]

Capping the OEM won't change the way the aftermarket one functions.

Capping the outlet is the best way. Just make sure it's fuel tight.

 

[spf_lexus]

Thats what I want, I am under the impression the stock unit is hampering the FMU's ability to do it's job. All I plan to do is remove vacuum line and cap manifold and regulator vacuum port. The next step I guess would be to completely get rid of it and blockoff. My take on it is the OEM regulator is already setup but it was never built for boost and using the rising rate has all kinds of adjustments that should be better off on it's own.

 

[Zuffen]

If you're not going to use it I'd get rid of it altogether as then it can't cause you any grief.