2000StreetRod
Moderator Emeritus
- Joined
- May 26, 2009
- Messages
- 10,562
- Reaction score
- 375
- City, State
- Greenville, SC
- Year, Model & Trim Level
- 00 Sport FI, 03 Ltd V8
Fuel pressure/temperature sensor
Based on internet explanations I've found on the 3rd generation fuel pressure/temperature sensor I assumed it was two simple devices: a pressure transducer with a variable resistance output and a thermistor similar to the engine coolant temperature sensor. The four pin electrical connector reinforced my assumption: two contacts for the pressure transducer and two contacts for the thermistor. Yesterday I measured pin to pin resistances to determine which two were associated with the pressure transducer. I was surprised that there were different resistance values for all pin-to-pin pairs so I searched the internet for the Bosch part number data sheet. I learned that the sensor is a fairly sophisticated device with only one output: relative pressure. The temperature probe is used internally by the active device (requires +5 vdc) to compensate the pressure output signal that is proportional to the pressure difference between the fuel port and the air port. Since the air port is used as a pressure reference I'm surprised that Ford connects it to the vacuum side of the throttle body plate. Connecting it upstream of the throttle plate would provide fairly constant pressure except for altitude changes. However, I've decided to follow Ford's example and connect mine to the vacuum side which varies significantly. The vacuum may prevent dirt and moisture from contaminating the pressure reference side of the sensor. The data sheet specifies the working pressure limit of the sensor as 500 kPa (72.5 psi). A vacuum of 22 inches of Hg equates to -3.9 psi relative to atmosphere so my 67 psi (72 psi with new fuel rails according to fuel block gauge) is approaching the limit of the sensor. I need to install a PWM motor controller to drop the fuel pressure to 65 psi. I may go even lower. I found a quote posted on the internet from the 2004 Explorer/Mountaineer Workshop Manual stating that the normal fuel pressure with the ignition on and the engine running or not running is 30 to 40 psi.
Based on internet explanations I've found on the 3rd generation fuel pressure/temperature sensor I assumed it was two simple devices: a pressure transducer with a variable resistance output and a thermistor similar to the engine coolant temperature sensor. The four pin electrical connector reinforced my assumption: two contacts for the pressure transducer and two contacts for the thermistor. Yesterday I measured pin to pin resistances to determine which two were associated with the pressure transducer. I was surprised that there were different resistance values for all pin-to-pin pairs so I searched the internet for the Bosch part number data sheet. I learned that the sensor is a fairly sophisticated device with only one output: relative pressure. The temperature probe is used internally by the active device (requires +5 vdc) to compensate the pressure output signal that is proportional to the pressure difference between the fuel port and the air port. Since the air port is used as a pressure reference I'm surprised that Ford connects it to the vacuum side of the throttle body plate. Connecting it upstream of the throttle plate would provide fairly constant pressure except for altitude changes. However, I've decided to follow Ford's example and connect mine to the vacuum side which varies significantly. The vacuum may prevent dirt and moisture from contaminating the pressure reference side of the sensor. The data sheet specifies the working pressure limit of the sensor as 500 kPa (72.5 psi). A vacuum of 22 inches of Hg equates to -3.9 psi relative to atmosphere so my 67 psi (72 psi with new fuel rails according to fuel block gauge) is approaching the limit of the sensor. I need to install a PWM motor controller to drop the fuel pressure to 65 psi. I may go even lower. I found a quote posted on the internet from the 2004 Explorer/Mountaineer Workshop Manual stating that the normal fuel pressure with the ignition on and the engine running or not running is 30 to 40 psi.