Adding an electric pump upstream to prime a mechanical pump as required is also fairly straightforward. This can control vapor lock on hot days in heavy traffic without needing to put an unnecessary continuous load on your charging system. Using the electric pump sporadically during starting should pose minimal issues on the electrical system. As with mechanical fuel pump replacement, the electric pump should be mounted as close as possible to the tank and as low as possible to allow gravity to prime the electric electric pump. Follow the installation instructions of the electric fuel pump's manufacturer.
The electric fuel pump setup in this case must be capable of flow-through operation. That is, it should pose a minimal flow restriction so that fuel will easily flow from the gas tank to the mechanical fuel pump when the electric pump is not running.
The Carter P4070 is a rotary vane electric fuel pump and requires the use of a bypass around the pump with a fuel check valve (PN 169-1002). (crack open pressure of 1 psi). For a new installation, the Carter P4602RV includes a pump, check valve, and additional fittings.
Airtex has a similar electric pump & bypass setup for RV applications. Airtex E8120) is a rotary vane pump that includes a fuel check valve (Airtex CV8000) but Airtex has confirmed that the CV8000 has a crack open pressure of 1-5 lbs (psi?), which may be excessive for fuel to readily flow to the mechanical pump. Airtex recommends their solenoid pumps, Airtex E8016S and Airtex E8012S for priming mechanical fuel pumps in 12V automotive applications.
Fuel Check Valves
| Carter 1/4" NPT |
Airtex 1/4" NPT |
Dorman 5/16" Hose |
Dorman 3/8" Hose |
Rotary Vane Pump with Bypass
| Carter P4602RV (9 psi, 50 gph) |
Airtex E8120 (5-9 psi, 40 gph) |
Solenoid Pumps
| Airtex E8016S (2.5-4.5 psi, 30 gph) |
Carter P74021 (3.5-5.5 psi, 15 gph) |
Mr. Gasket 42S (2-3.5 psi, 28 gph) |
Edelbrock 17303 (2-3.5 psi, 30 gph) |
| Airtex E8012S (5-9 psi, 30 gph) |
Carter P74019 (5.5-9 psi, 20 gph) |
Mr. Gasket 12S (4-7 psi, 35 gph) |
Edelbrock 17301 (4-7 psi, 38 gph) |
Because the electric fuel pump is only required to combat vapor lock, the operation of the electric pump may be controlled by the driver with a simple toggle switch that is powered by the Ignition Run circuit. The fuel pump's noise should indicate with the pump is running.
Another method to control the operation of the fuel pump is to wire it with a relay controlled by the Ignition Start circuit. This ensures that the electric fuel pump operates whenever the engine is started.