Fuel Pressure and Flow

the fuel pressure and flow are one of the most important parts of the injection system, this depends on how much fuel gets squirted into the injectors.

before i started this test, i checked the specifications of the fuel pressure for this engine (4A-FE). the pressure was 38 to 44 PSI. I then did a visual check to make sure there was no leaks in the system.

i then measured the fuel pressure of the engine with the ignition on but the engine off, there was no pressure because the engine had not been on.
then i turned the engine on and let it idle for a few minutes and found the pressure raised to 36 PSI.
after that i clamped the fuel return line to find that the pressure went off the scale to above 87 PSI.

the next test i did, i took off the vacuum line and blocked it so the engine thought it was at wide open throttle, this brought the pressure to around 45 PSI.
i then turned the engine off but left the key on and watched the pressure drop to 37 PSI, this is the residual pressure.


if the engine had low fuel pressure the vehicle would have a rough idle and be running lean, this would happen because the injectors would not have enough pressure to squirt the right amount of fuel into the combustion chamber. this could mean that the pressure regulator not letting fuel rail build enough pressure and could be stuck open or a faulty fuel pump.

If the engine had a high fuel pressure, this would mean the vehicle would have a boggy idle because the engine would not be burning the fuel properly, this would be creating carbon monoxide. the injectors would be squirting too much fuel into the combustion because the pressure would be too high, this could also cause the injectors to dribble. this could mean the pressure regulator is stuck closed and not allowing pressure out into the return line.