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Boost BRZ / 86 / FRS - Return Style Fuel System and the High Pressure Fuel Pump - EcuTek Help

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I have a BRZ that is happily running about 8psi boost pressure, and looking to push upwards of 20psi.

The car currently has it's returnless fuel system with the factory nominal line pressure of 4bar (58psi). That means I get a bit of extra pressure differential across the injectors at idle (forcing me to use smaller pulse widths than i'd like), and a little less under boost.

I'm concerned that when running higher boost, the differential pressure across the port injectors will have dropped down to ~38psi from it's nominal 58psi, and the injectors (ID1050x) may start to perform poorly or run out of head room. A return style fuel system using a pressure regulator with manifold boost/vacuum reference should fix this by regulating the rail pressure to keep the nominal 58psi across the port injectors at all times, but his might cause some other issues.

This car is using EcuTek to tune with the factory ECU. I believe the "Port Injector Manifold Relative Pressure Comp" table is a 2D table, with "manifold pressure" as the input, and "PI volume amount" as the output as an adder to the total fuel volume requested. I believe the OEM setup used this to comp for non WOT conditions, where manifold vacuum would increase the differential pressure across the port injectors, supplying more fuel than otherwise expected. This table also doesn't initially extend past atmospheric pressure since FI wasn't intended.

With a return system that utilizes a manifold pressure referenced regulator, should I be setting the entire "Port Injector Manifold Relative Pressure Comp" table to zero? (since the differential pressure across the port injectors should be neat constant)

Also, what effect will varying the line pressure with this style fuel system have on the high pressure fuel system? I believe it won't have a significant effect. My understanding is that the high pressure fuel pump is a positive displacement pump that close loop regulates its rail pressure using a pressure sensor in the high pressure line, and varying the open time on the high pressure pump inlet valve solenoid. Any comments/concerns?

Thanks!

Hi Raul, I am having the same question here, has Andre or anyone answered your question?

Hi Yuchen,

Nobody ever responded actually.

I can tell you my results, having run this car with returnless and return style systems, with and without manifold reference.

I'm short, for my setup using the ID1050x injectors and Borg Warner 7163 at ~25psi boost, do whatever you want. All of the fuel system configurations have worked fine on 93 gas and E85.

No issues with the high pressure fuel pump. Factory like idle is pretty easy to achieve even without manifold reference and there was still injector head room as well.

I do prefer a return style system. I ended up using the kit from radium to get my fuel filter and regulator easily accessible.

Good luck!

Raul,

I'm glad you found your way to the right setup. Radium makes great product and yes at that boost level you'd want to run return style with a 1:1 FPR to avoid low differential fuel pressure in boost causing poor fuel atomization, inconsistent fueling.

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