Fuel Pump and Fuel Consumption

[Hikaru]

Hi all

is fuel pump had something to do with fuel consumption in injection engine?
like higher the pressure give more mpg?

because after I replace my fuel pump (with not the original) for my 5AFE engine, it become very low mpg

before I replace the fuel pump (original) I’ve got 12 – 16 Km/L = 28 – 37 mpg
after I replace the fuel pump (non original) I’ve got 5 – 6 KM/L = 11 – 14 mpg

is that coming from the fuel pump or i have another case (eg: Bad spark plug or carbonated cylinder)?
I’ve pull code from the diagnostic, and it show normal engine (no code show)
I’ve check the Air filter, MAP sensor, Thermal Sensor, Coil, CDI, (there’s no MAF sensor, Knock sensor , O2 sensor at my engine).

thanks

Topic

[Lorrin Barth]

Does you vehicle have a fuel pressure regulator?

[Hikaru]

Yes it has, and I “think” it still working
is the FPR, 1 of many suspect?
what’s the symptom if FPR broken
I already check it by remove the hose from intake plenum/manifold and not smelling any gas from it, so i think it not leak, or is there any more test to do with it? (i don’t have vacuum tools)

thanks

[Lorrin Barth]

You say this started with the replacement of the fuel pump. Ordinarily it doesn’t matter what the fuel pump delivers so long as the pressure regulator can drop the pressure to the pressure needed at the fuel rail. If the pump is delivering way in excess of normal it could overrun the ability of the regulator to return fuel to the tank. The test here would be to measure the fuel rail pressure comparing it to the maker’s stated value. This will also test the operation of the regulator.

Any kinks in the return line will cause problems.

The fuel pressure regulator needs good vacuum off of the manifold. This vacuum hose is the most important one on the vehicle. If the line is disconnected or leaking the vehicle will run rich. Some vehicles have a solenoid in the vacuum line that opens the vacuum line to atmosphere for hot start. If the solenoid fails in the open position this will cause a rich condition. The test here is connecting a vacuum gauge at the fuel pressure regulator looking for normal manifold vacuum.

[Hikaru]

The engine work’s fine with the non original fuel pump, looks like it have more power.
and yes that’s what i feel, the mix felt more richer, and i don’t have vacuum gauge to test it.
is there any chance the FPR broken even it not leaking from the vacuum hose? (eg : not open even it had vacuum)
my FPR is vacuum base, not the electrical solenoid.

[Lorrin Barth]

Fuel pressure regulators do fail however it seems somewhat unlikely it would fail at exactly the same time the pump was replaced.

Vacuum gauges are very inexpensive.

All (all may be too strong of word) fuel pressure regulators are vacuum operated. What I was referring to is another device that might be located between the manifold and regulator on the vacuum line that is electrically operated to monetarily raise fuel pressure during hot start. It should be easy to tell if your vehicle has one, just trace the vacuum line.

[Hikaru]

Oh, my engine does not have the device, the hose direct connect to the manifold.
ok then I’ll try to replace the FPR (very expensive tinny device (>_<) )
btw do you know how to test it without tools?
i thinking to redirect the return hose to a bottle so i can see any return gas (if i see gas in the bottle then the FPR still working, if not, FPR fail, can it be done (safely i mean)?

[Author]

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