This
is the Vortech Auxiliary Fuel Pressure Regulator (AFPR) aka Fuel Management Unit
(FMU) supplied with the basic Greddy turbo kit for the 1.6 Miata. Number stamped on bottom is 6Z110-120. Believe it is a 12:1 disk. But after initial
testing a few years back remarked it acted more like a 10:1 disk. The fuel pressure should rise by 12 PSI for
each 1 PSI of boost the intake manifold senses.
Am not an engineer, so can’t explain how it was all machined and
calculated.
The signal line is parallel to both the stock FPR and the Vortech and the fuel flow is in series between the fuel rail (stock FPR} and the fuel return line. This means can never lower fuel pressure below what the stock FPR clamps. It is also invisible to the fuel system when any vacuum or atmosphere pressure is sensed in the intake manifold. It only reacts to boost pressure. More on test results and opinions later, for now will take it apart and look inside.
Top
section is removed by using a 4mm Allen (hex) Wrench. The very top section has the fitting for the
signal line, can unscrew it if you like.
Underneath is the flexible diaphragm, the metal disk, and the lower
chamber. The sliding piston in the
center is what gets pushed down to clamp the return line.
Notice the small hole at about the 2 O’Clock position on the bottom section. This keeps everything below the upper diaphragm vented to atmosphere.
Remove
the remaining 4 mm hex screws. One screw
is already removed and that vent hole is just barely visible at about the 8
O’Clock position.
In the center is the sliding piston. Is just resting in place, and slides in and out easily.
In
the lower chamber, the offset hole is the fuel feed from behind the stock
FPR. The center hole is the last thing
fuel sees before it’s return back to the fuel tank. The piston pushes down that thin metal disk
to restrict fuel flow and raises fuel pressure beyond the stock FPR when boost
is applied.
Not shown is the flexible diaphragm that fits over the metal disk to seal the middle and lower chamber. The only thing fuel comes in contact with is that area between the two holes and one side of the thin and flexible metal disk.
A common error for new installs is hooking up the two lines backwards. It won’t work properly. If the unit has been in and out a few times or if fails to raise fuel pressure, suggest taking it apart and cleaning out the small chamber. Little bits of chewed fuel line can be pinched on the small center lip and ruin the proper seal.
A
view from the top of the unit after disassembly. Caution when installing that small O Ring
that fits on the lower chamber. It is
easy to lose or deform during assembly.
With
all the pieces turned over, is fairly simple to see how it works.
Used
various gauges for the testing. The Mighty-Vac
was used to fake boost and vacuum to the AFPR signal line. Was also used to check the vacuum readings on
the installed Boost/Vacuum gauge.
The installed Autometer electronic fuel pressure gauge is too awkward to read, so will use the Lincoln mechanical gauge. Meaning the Autometer is safer to use and good for a ballpark reading, but less accurate because of the small sweep and damping action.
Testing included the stock FPR under boost/vacuum conditions, testing the stock fuel pump, the additional Pierberg pump, and the impact of boost and vacuum on the Vortech unit with and without the Pierberg. Initial testing was done in "Prime Mode" and later road tests confirmed the near identical readings.
An
old picture used on other pages. Shown
with a 100 PSI mechanical gauge, but I swapped it out with a 160 PSI gauge for
this testing.
Again, about $20 at NAPAwill get everything shown here. Just tell the guy at the counter you want a temporary gauge to read fuel pressure on a 5/16” fuel line. Let him chase around and get all the fittings and parts needed. The longer hose is to tape gauge on the windshield for a final road test.
Removed the BEGI and installed the Vortech.
OK here are the results, and letting everything fall as I found it.
The stock fuel pump on my ’90 still puts out 85 PSI. Testing several other Miatas found the fuel pressure all within 78 to 86 PSI.
With the Pierberg added, maximum pressure available was in excess of 140 PSI. Repeated several times had slightly different readings by a few higher PSI, but that is close enough and way more than is needed. Never knew that before since the 100 PSI gauges used previously pegged.
Idle fuel pressure simulated at 21 hg vacuum produced about 35 PSI pressure clamped by the stock FPR. By slowly venting to atmosphere, fuel pressure rose to around 43 PSI. Repeated several times with some minor variations. That is pretty much in line with multiple other Miatas tested. Stated from previous posts the pressure jumped by 5 to 10 PSI. Both mechanical gauges used read a few PSI higher than the Autometer electronic gauge. Have not found any two Miatas with identical pressure readings, but should be close enough, and extremely insignificant when ECU is in closed loop.
With combinations of the Pierberg and Vortech added, no changes were noted in the stock FPR clamping ability. This confirmed by earlier findings when stating the both those devices are invisible to the fuel rail while intake manifold is in vacuum or atmosphere pressure.
I tested the stock FPR as a stand alone item simulating up to 20 PSI boost. Repeated it several times and a couple of times had a slight tic of maybe 1 PSI additional fuel pressure. For practical purpose would say the stock FPR is also invisible at pressures over atmosphere.
The fun part. The Vortech still acted more like a 10:1 disk with a few quirks. By slowly faking boost to a combination of Vortech and stock FPR, the Vortech did nothing until about 1 ¼ PSI to 1 ½ PSI. At that time it shot up and added from 15 to 20 PSI fuel pressure. By a little under 4 PSI, the fuel pump maxed out around 85 PSI. During an actual road test this was too difficult to stabilize and read clearly. I would guess that with the Vortech would run lean at boost onset, run too rich up to 4 or 5 PSI then lean out properly at about 6 PSI of boost.
Then spliced in the Pierberg and did the same test. Found another odd quirk. At around 5 PSI boost was in the low 90 PSI fuel pressure. At about 5 ½ PSI boost the fuel pressure shot up to 120 PSI fuel pressure. At 7 PSI maxed the Pierberg out at 140 PSI of fuel pressure.
In fairness have never tested a different Vortech. Unknown if these results are typical. In 4 years it was only installed twice and that was for testing only. Results were consistent both times. It has less than 20 miles of actual road use.
My summary stands a posted earlier. The Greddy kit was designed for 4 to 5 PSI boost and should work fine out of the box and last a long time. If happy with those boost stages, suggest not spending more money for things like recalibration kits, bigger injectors, or higher flowing fuel pumps. Seems when you start doing these things will just end up adding a string of bandaids to cure other adverse symptoms. If planning to stay with an AFPR system, suggest looking into a fully adjustable AFPR such as the Vortech Super FMU or BEGI prior to changing the boost. This is my opinion for what it is worth!