Setting Fuel Pressure on DI/Port Systems with Two Regulators
Gen3 and Gen4 Coyote motors (2018+ Mustangs and F-150) are fueled by Direct Injection (DI) and port injection. These two systems are fed with the same low pressure feed line and fuel pump, but the DI pump has different inlet requirements than the port injectors. Two regulators operating with different settings can optimize the requirements of both of these injection systems, often gaining 150+ whp of capacity with E85 over a single regulation strategy. For the case of simplicity, this article will only cover the setting method of the regulators of a fuel system that is already installed. Here is the setting procedure:
- The fuel pressure should be set with the engine off and the primary (full-time) pump configuration running. (i.e., if you run one primary pump, then that pump should only be running; if you run two pumps full time, then both of those pumps should be running) Setting the pressure with the motor off will stop the fluctuating fuel pressure (due to the pulsing of the HPFP) and will not impart a vacuum influence on the second regulator. You must jump the relay(s) or FC2/FC3 so the pump(s) runs with the engine off.
- Adjust both regulators to the lowest pressure settings, but without letting the adjustment screws fall out. (should be around 20-28 psi)
- Adjust the first regulator (after the HPFP / T-block) to set it to 58 psi. Set the jam nut. This regulator should have a filter plug installed on the MAP port.
- Then, adjust the second regulator (after the port injection rails) to 43-48 psi. Set the jam nut. This regulator should have a boost reference line connected to the intake manifold.
- Disable the jumper that was installed in step 1.
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