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Fuel Pressure Regulator Installation Instructions

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Cartech Rising Rate
Fuel Pressure Regulator (FMU) Installation Instructions

Purpose of the Rising Rate Regulator
The Cartech regulators are designed specifically to add fuel to modified EFI engines (turbos, superchargers, and normally aspirated). This is accomplished by using the manifold vac/pressure to drive the fuel pressure up as the boost rises, or with the N/A engines, as the vacuum goes toward atmospheric.  The three types have differing part numbers.

Types of Regulators
PN: 2025 Aftermarket turbo and supercharger (1/8 NPT)
PN: 2027 Hi-Flow aftermarket turbo and supercharger (1/4 NPT)
PN: 2022 Factory (OEM) turbo and supercharger
PN: 2023 Normally aspirated

General Information
1.) The rising rate regulators fit into the fuel system after the stock regulator, and in series with it.  The regulator becomes the last item before the fuel returns to the tank.  Do not remove the stock regulator, as it still controls the fuel flow under most manifold vacuum conditions.

2.) The regulators can be mounted in any position. For convenience, place the adjustment screws within easy access. The most difficult aspect of installation is getting the fuel lines onto the correct fittings.

3.) Older model regulators made from castings (20002-20007), had labels of  “IN/OUT” on the barb bosses.  “IN” is for the fuel line from the stock regulator.  “OUT” is the return line heading back to the fuel tank.  The “IN” and “OUT” of the new regulators (2022-2027) are slightly different, as there is only an "IN" label. The blank port is the "OUT" port.

4.) Fuel fittings for the 2022, 2023, & 2025 are 1/8 NPT.  The 2027 has 1/4 NPT threads. Some form of thread sealant is advised. We prefer one drop of Loctite per joint. In general, please avoid teflon tape as the residue and debris can get into the fuel system if not extremely careful. The threaded bosses on the regulators are strong enough for a zillion ft-lbs of torque, they will not crack.  They can be stripped, but neither failure is warrantable.

Signal Lines
The regulators are powered by manifold vacuum and pressure.  The signal must come from the intake manifold, after the throttle plate.  These will not work properly if the signal comes from anywhere else.  There are two small hoses attaching to the regulator.  The hose barb pointing directly at the center screw of the regulator is for the manifold signal line.  The other hose barb fitting, exiting the brass needle valve, is the fitting for the check valve. 

On occasion the regulators will not adjust to a sufficiently low rate of gain.  In this instance, it is necessary to add the small restrictor to the signal line. This is provided for your convenience. The restrictor is non-directional, it can point either way.

Check Valves
Two functions are accomplished by the check valve.  One, the simple plugging of a small vacuum/boost leak.  Second, vacuum is required to pull the preload spring under the center screw away from the valve so stock fuel pressures can be achieved under manifold vacuum conditions. The check valve white end attaches to the 4" vacuum line and the line plugs onto the 10/32 hose barb exiting the needle valve. This allows venting the boost signal to atmosphere in order to adjust the rate of gain, while maintaining a seal under vacuum conditions. The black end of the check valve MUST blow off to atmosphere and MUST NOT be attached anywhere else.

Please keep in mind that the OEM or aftermarket status of the vehicle doesn’t change if one swaps turbos on an OEM automobile. It is OEM because the fuel system was designed for forced induction  originally.  That status doesn’t change unless one changes the fuel system in some manner.

Only one adjustment is required of the NA and OEM turbo/supercharger regulators, whereas the aftermarket turbo requires two adjustments.  For the NA/OEM regulators, only the maximum pressure achieved is of interest.  For the aftermarket, both the point of onset and the maximum pressure are adjusted.

In all installations, we urge tuning be aided with an air/fuel ratio meter and  fuel pressure gauge.

Pump Requirements
The pump pressures needed to run the rising rate regulators vary with each type.  The 2023's for the NA engines do not need much pressure and are always compatible with a stock/original pump, provided it is in proper condition.  The OEM turbo/sc style units (2022) need pressures in the 70/80psi range to function well, while the aftermarket turbo/sc (2025/2027) will need a minimum of 95 psi for 7 to 8 psi boost.  Checking the pump is discussed later.

NA Regulator, 2023
For the NA regulator, the center screw is the only adjustment possible. It determines the fuel pressure achieved at full throttle.  Turning the screw clockwise raises the fuel pressure. There is no needle valve, check valve, or restrictor included with the 2023. All 2023 adjustments are made at idle with the signal line removed.

An approximate graph of fuel pressure is shown in figure 2023.  This is an approximation only for the purposes of suggesting to you the general ranges of operation.

                                         Figure 2023
                      50                                                                *
                      48                                                         *
                      46                                                   *
Fuel               44                                            *
Pressure         42                                   *
                      40                             *
                      38                       *
                      36              *
                      32     ------------------------------------------
                               12    10     8     6     4     2     0
                                        Manifold Vacuum

OEM System Regulator, 2022
The OEM turbo/supercharger requires more fuel if the boost pressure is raised beyond the factory level.  Additional fuel is only required for that extra increment of boost, and not through the entire boost operation.  This adjustment is controlled solely by the needle valve.  The amount of increase required is modest and is suggested by figure 2022.

                                                 Figure 2022

                      75                                                                            *
                      70                                                                  *
                      65                                                          *
                      60                                                  *
Fuel               55                                        *
Pressure         50                               *
                      45                        *
                      40               *
                      30 ---------------------------------------------------------
                                  2     4      6      8      10      12    14    16      18

                                                     Boost Pressure

Aftermarket Turbo/Supercharger Regulator, 2025 & 2027
Two adjustment are necessary with this regulator. NA engines that are subsequently fitted with forced induction often exhibit extreme leanness in the range of 4 inches of vacuum to approximately 3 psi boost. The cause for this is that the turbo/sc can achieve atmospheric pressure in the manifold prior to the throttle being fully open.  Under these MAP/MAF and TPS combinations, the ECU lacks proper enrichment and a lean condition occurs.  This is not as prominent in later model ODB2 automobiles where the O2 sensor feedback covers a broader range.

Pressure calculation: the fuel pressure required increases with the square of the boost pressure ratio:
Example:   6 psi boost is a pressure ratio of 1.41. With stock fuel pressure of 36 at zero boost, then:

 Needed fuel pressure   = (PR2  x Base Fuel Pressure) + Boost  = (1.412 x 36) + 6  =  77.5 psi

The first adjustment is of fuel pressure is at the atmospheric pressure point, and can best be done at idle.  To simulate passing through the zero point, the vacuum line must be removed from the regulator. The regulator then sees atmospheric pressure as a signal, same as zero on the boost gauge.  Control of the fuel pressure at the zero point is by the Allen screw in the center of the regulator. Clockwise on the screw will raise the pressure.  Once adjusted, plug the vacuum line back onto the regulator and observe the fuel pressure drop to the stock figure. A suggested pressure for starters is 48 to 50 psi. Please understand, this will vary from engine to engine, and is not a magic number.  The “magic” number is whatever pressure your vehicle requires to pass thru the boost onset without the lean flat spot.  It is not unusual to see pressure anywhere from 40 psi to 55 psi.  Use whatever works best.

The second adjustment, the needle valve, controls the rate of gain of fuel pressure versus boost pressure. The lowest rate of gain is with the needle valve fully open, the highest, fully closed.  Clockwise closes the needle valve.  Figure 2025 offers a typical guide to fuel pressure versus boost pressure.

Caution: There is a vague limit that exists with regard to the maximum possible fuel pressure.  The industry "rule of thumb" of injectors jamming at 50 psi and the flow not increasing with pressure is not correct.  It is possible for a very large injector (90 + lbs/hr) to jam at 100+ psi of fuel pressure. At anything less than that, jamming is not going to happen.

                                         Figure 2025

                      120                                                                                     *
                      100                                                                   *
                        80                                              *
Fuel                 60                     *
Pressure                 *

                        20  -----------------------------------------------------------
                              0       1     2     3       4       5      6     7       8       9    10

                                                  Boost Pressure

Checking Pump Pressures
A brief check of the maximum fuel pressure available should also be done at idle. This is essentially determining the pump’s pressure capability.  None of the regulators can force a pump past it maximum pressure potential. With a pair of pliers, squeeze the fuel line shut that connects our regulator to the original fuel pressure regulator.  When squeezed shut, the pump will be forced to maximum output. Make sure the pressure available is consistent with your intentions.  In all cases, the pressure must show, in this idle test,  to be about 10 psi higher than the desired fuel pressure, as the available pressure under real load conditions will be less than that measured at idle.  This test does not actually prove the pump to be adequate under boost, but if it doesn’t pass this test, it is certainly a waste of time to continue with the same pump. In general, do not try to exceed 100-110 psi fuel pressure.

The maximum fuel pressure is controlled by the needle valve and must be determined while driving the car under boost.  Start with the needle valve closed, which is fully clockwise. It is unlikely the regulator will need this adjustment, but the test also serves the purpose of proving the pump will do the job needed. A weak fuel pump will cause a drop in fuel pressure as the engine is revved higher.  If the pump cannot maintain the desired psi to the engine redline, it is not in satisfactory condition to feed the turbo/sc engine and must either be replaced or supplemented with an auxiliary pump.

Trouble Shooting

1. Jams at maximum fuel pressure:

The regulator is installed backwards.

The center screw in bottomed out inside and must be backed off.

2. Pressure doesn’t rise:

No signal.

Signal is blocked.

Pump won’t make any more than that pressure, close the fuel return line to verify.

The check valve is stuck open. Test by closing the needle valve and sucking on the signal line. It should be a dead end.

3. Pressure rises, but not enough:

Close the needle valve.

Increase the center screw (static) adjustment.

Check the pump again, but remember, it will have less pressure at high loads, than at idle.

Remove the restrictor.

4. Pressure rises, but too high:

Open the needle valve further.

Back off the center screw somewhat.

Add the restrictor.

Check valve is installed backwards.

5. Fuel pressure oscillates:

Slow oscillation of ~1 Hz can result from the regulator being installed backwards.

Faster oscillation, more like a buzz, but without the noise, is usually induced by a rapid pulsation from the fuel pump.  Not much can fix it short of a different brand of pump or a pulse damper. The condition is not harmful at boost pressures of 8 psi or less.

If buzzing is audible, turn the center screw 1/4 turn, and it ususally ceases.

6. Regulator buzzes under boost:

This fault occurs occasionally when fuel pump and manifold  pressure oscillations overlap to reinforce each other.  Usually, it can be quieted by turning the center screw one or two flats.  If it cannot be quieted in this way, return the regulator to us for an overhaul or replacement.

Warranty: The regulators are warranted for workmanship and function for one year from the date of shipment from our facility.  No open threads, user installed threaded items, or adjustable threads are warranted in any way. If problems arise from using teflon tape, Cartech reserves the right to refuse warranty coverage for damages caused to the regulator.

As always, if none of the above is effective in tuning your regulator, give us a call at the number below. If needed, return the regulator to us for service.

Copyright 2002 Bell Experimental Group, Inc.
Copyright 2002 Cartech Systems LLC

Cartech Systems
1026 Grubb St.
San Antonio,  TX  78219
        Tel: 210-333-1642       Fax: 210-333-1749

Telephone: 210.333.1642
FAX: 210.333.1749
Postal address: 18975 Marbach Ln, Suite#812, San Antonio, TX 78266
Sales E-mail: Mike Montgomery

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Last modified: 05/30/03