Originally posted by Lance Kinley:
Ok, makes sense.
However, I'm only seeing 9V on the fuel pump harness on one wire, and 9.8-12V on the other, depending on when the key is turned. I think it puts in 12V when the pump is active and 9.8V when idle.
Just wondering if the other one with a steady 9V is normal.
-Lance
variation in voltage is how computer controls pressure. Decrease voltage, motor turns slower, pumps less fuel, pressure drops.
9v is likely the preset voltage value used during times when extra pressure is not required.
as for low press. check the regulator first, but I think that it may be the motor, especially if your car is high mileage. The motor is DC so it has brushes, and if you have high miles then the brushes are worn, therefor their pressure on the commutator is less and the brush bounces allowing for arcing between commutator blocks thus lowering operational efficency of the motor causing a lower RPM at 9v and therefor lower volume output, and with the resriction the same (press. reg.) pressure will be less.
But then again the regulator should compensate, unless the motor's performance has degraded to a point where the pressure regulator has compensated as much as possible and the regulator needle is at its seat and cannot close more allowing for further compensation for motor performance degredation. Which makes sense that the regulator would not have the ability to close completely, becaue if it did it would block flow and engine would stall, but if it has a limit as to how far it can close then if it were to fail and the electric pump were still operational the engine would still run, but not be able to produce it max power output due to lack of fuel.
