n0v8or
10 Year Member
YtnGT - your description of the system is pretty darn accurate. It's not as precise as you might imagine, because the PCM can compensate for variations in differential pressure "on the fly", and recalculate every individual injector pulse.
Regarding the black relay in trinityGT's post, it's a standard Bosch automotive relay capable of switching up to a 30A lamp load. These cost Ford less than a buck in quantity. A relay that can reliably switch an inductive (fuel pump) load and operate during cold cranking is a little more expensive - like $1.20. The diagnostics are EPA mandated and must be OBD2 compliant; that adds a 50 cent serial transceiver IC, plus an 18 cent power conditioning IC. Add to that a housing, bracket, and connector, and the whole deal represents less than $2.50 in Ford (actually Visteon, who builds the Ford modules) cost.
In comparison, the PWM fuel pump driver IC with integral OBD2 port costs $1.38 and the driver MOSFET 17 cents (my company makes both). Add in the PC board, housing, bracket, and connector, and the total easily meets or beats the relay solution. What finally tips the scale is warranty labor costs . . . the mechanical relay has 2X the failure rate of the solid state module over the emissions warranty period.
Regarding the black relay in trinityGT's post, it's a standard Bosch automotive relay capable of switching up to a 30A lamp load. These cost Ford less than a buck in quantity. A relay that can reliably switch an inductive (fuel pump) load and operate during cold cranking is a little more expensive - like $1.20. The diagnostics are EPA mandated and must be OBD2 compliant; that adds a 50 cent serial transceiver IC, plus an 18 cent power conditioning IC. Add to that a housing, bracket, and connector, and the whole deal represents less than $2.50 in Ford (actually Visteon, who builds the Ford modules) cost.
In comparison, the PWM fuel pump driver IC with integral OBD2 port costs $1.38 and the driver MOSFET 17 cents (my company makes both). Add in the PC board, housing, bracket, and connector, and the total easily meets or beats the relay solution. What finally tips the scale is warranty labor costs . . . the mechanical relay has 2X the failure rate of the solid state module over the emissions warranty period.