I have an ASE A1 test question for you…
Technician A says that fuel pressure on a port fuel injected vehicle can vary 20 to 30 psi according to the load on the engine. Technician B says the fuel pressure should stay in a constant range and never vary more than 5-15 psi. Who is correct?
A) Technician A
B) Technician B
C) Technician A and B
D) Both technicians are wrong
The answer is B, Technician B is correct.
Fuel pressure should remain relatively constant at the rail in a range specified by the manufacturer. This spec can be found in the service information and even as a data PID parameter using a scan tool.
So, what changes when the driver mashes the pedal to the floor? It is how long the injector stays open. If the fuel pressure at the rail drops considerably when the engine is under load, the amount of fuel injected into the cylinder will also decrease.
The goal of any pressure regulator or pulse-width modulated control signal is to keep the pressure constant and predictable.
If the fuel pressure drops under full or partial throttle, the engine could experience a lean condition. This could cause hesitation, misfires and engine stumble. Some vehicles will set the trouble code P0087 for fuel or rail pressure too low.
This video is sponsored by Carter Engineering.
