IT IS HERE.  The advanced Fuel Pressure Regulator check valve for TokenSolutions.

This advanced check valve system via TokenSolution customization allows your FPR to see positive boost pressure, but never vacuum.

- In detail -

Most all modern cars employ returnless fuel systems, or in some cases have a return system but the FPR references from atmosphere.  When tuning a piggyback controller, you are using the highly calibrated and tuned OE original fuel maps in vacuum for ease of tuning, MPGs and the perfect a/fs they offer for cruising, tip-in, cold starts etc.  When one upgrades the returnless or atmospherically referenced fuel system to a 1:1 or raising rate return system, not only is the fuel pressure increased in boost as desired, but will also have a fuel pressure decrease proportionate to vacuum that is undesired.  This throws off fuel maps and trims and makes tuning in vacuum difficult, requiring map cel by cel corrections! 

When trying to employ a regular automotive check valve to prevent this vacuum caused issue, the check valve will 'lock' boost pressure in the FPR's reference line and cause the fuel pressure to be 'stuck' at the highest achieved fuel pressure, no longer making it proportionately increase pressure per manifold pressure as desired.

This issue is more evident with TRD supercharger systems that are bolt on replacements of OE intake manifolds and do not provide a boost only reference, as the supercharger system is down stream of the throttle body.

As demonstrated on the TS 2001 TRD supercharged Tacoma utilizing the "free FMU mod", the once messy vacuum tuning regions to compensate for the varying fuel pressures is now zero'd out, and a/fs and fuel trims are consistent.  This increases MPGs and reduces carbon build-up from the brief instances when the motor runs outside of optimum a/fs before closed loop trimming fixes it.

Absolutely essential for TRD supercharger setups such as the 3.4 and 3.0 systems and Alpine S/Cs for the 4cyl Toyota Trucks, and takes the pain and expense out of un-installing turbo pressure side piping and having barbs installed or allowing you to use an available port from a vacuum/boost manifold.  Enjoy far easier tuning, MPGs and reduced carbon build up.