Radium FPR Kit RA-Series | 1999-2005 Mazda MX-5 Miata (20-1022)

The 99-05 Miata runs a returnless fuel system with no way to touch fuel pressure, which is a problem the moment you add boost or E85.

The Radium Engineering RA-series FPR kit for the 1999-2005 Mazda MX-5 Miata adds an adjustable fuel pressure regulator that works with any fuel pump hanger, including the factory returnless NB setup. The regulator mounts near the EVAP charcoal canister on OEM threaded studs, the OEM fuel feed line from pump to filter is reused unaltered, and two new 6AN lines run to and from the FPR. A 0-100 psi gauge mounts adjacent on the feed line for adjustment, and a stainless SAE quick connect plug blocks off the tee on the OEM feed line. No permanent modifications, fully reversible, and compatible with all gasoline types plus methanol, ethanol, and E85.

What You'll Feel

• Fuel pressure you can actually set and read on a chassis that offers neither from the factory
• 1:1 rising rate response under boost, or locked constant pressure with the included vacuum plug if you want OEM behavior
• Vacuum port aimed wherever your install needs it, thanks to the 360 degree swiveling double O-ring sealed reference port
• A completely reversible install using OEM studs and the OEM feed line

Features

• MPR-RA fuel pressure regulator with 360 degree swiveling vacuum reference port
• 0-100 psi fuel pressure gauge mounted on the feed line
• Four interchangeable 10-32 vacuum port fittings: 3/16 inch barb, 3AN male, push-to-connect for 1/4 inch OD tubing, and a vacuum plug for constant pressure
• Stainless steel mounting bracket, anodized aluminum fittings, SAE quick connect fittings, hose clamps and hardware
• 6AN (3/8 inch) fuel hose and a stainless SAE quick connect plug for the OEM feed line tee

The Details

The NB regulates fuel pressure at the pump module, so adjustable control means taking the OEM regulator out of play. This kit does that two ways: paired with the Radium 20-1020 fuel pump hanger, whose install removes the OEM regulator and makes an aftermarket FPR mandatory, or on the stock hanger, where the instructions detail bypassing the OEM FPR. Radium's other plug and play path is the full 20-1025-03 / 20-1025-05 fuel hanger plumbing kit, which bundles an RA-series regulator with complete tank-to-rail plumbing; this kit is the lighter option when regulator control is the goal. If you want OEM-equivalent constant pressure rather than rising rate, install the included vacuum plug. Pair with the Radium 1.8L BP fuel rail (20-0369) and the 99-05 rail plumbing kit (20-0423), both carried here. On 89-97 cars this kit is unnecessary, since the OEM regulator sits on the fuel rail and is unaffected by hanger installs.

Kit Includes

• MPR-RA fuel pressure regulator and 0-100 psi fuel pressure gauge
• Stainless steel mounting bracket, anodized aluminum fittings, SAE quick connect fittings
• 6AN fuel hose, hose clamps, and hardware
• NOT included: the fuel pump hanger, fuel pumps, fuel rail, and injectors

Applications

• 1999-2005 Mazda MX-5 Miata NB, with the Radium 20-1020 fuel pump hanger or the OEM hanger

Important Notes

• A rapid fuel pressure drop after the pump shuts off is normal for aftermarket regulators of any brand and is not a defect; pressure resets immediately when the pump is activated again. Long cranking or slow pressure build while cranking points elsewhere, typically to feed hose drain-back from an internal pump module leak or a missing pump check valve
• Use a wicking medium-strength threadlocker when installing the vacuum fitting