The wire to fuel pump is not having current I therefore bypass it. Can a car consumption increase if ecu is bypass?

2 Answers 2


Whoa. I believe that car is fuel injected and fuel pump pressure is a big deal. Now here's the issue.

Older fuel injection cars (1980's and early 1990's) had TWO lines/hoses running between the fuel tank and the engine. A fuel supply line and a fuel return line. The pump ran all the time and pressure was controlled on the fuel rail at the engine. Excess pressure was controlled by letting some fuel return to the fuel tank. The problem with this was running the pump all the time doesn't help your fuel economy AND it generates fuel vapor inside the gas tank. If that vapor escapes to the atmosphere that's really bad for planet earth.

Newer vehicles have ONE fuel supply line. Fuel pressure is controlled by the pump. The way to do this is with a Pulse Width Modulated (PWM) controller. The PWM system is controlled by the engine computer and allows the fuel pump to put out partial load. There is no return line from the engine back to the fuel tank.

This PWM thing is s big deal. I'm guessing you have a one line system and your fuel pump control module (with its PWM internals) has become defective. You need to replace that module. Running the pump 100% would be bad. Really bad. I'd worry you start breaking fuel injectors. Additionally the pump won't last very long, not very long at all.

If you do have a two line system , and you can see a fuel pressure regulator on the end of the fuel rail then you are probably okay. The pressure regulator is a metal can about the diameter of a coke can and about 1/4th as tall as a coke can. The fuel tank return line is directly attached to this can.

Let's us know how the troubleshooting and repair goes.

  • Thanks for the response. You are right fuel supply has one line.So where can I locate the fuel pump module you are talking about. This is a 1997 Toyota corolla. Commented Apr 25, 2017 at 15:58
  • I'm doing an online search, and I'm finding nothing on that make, model, year showing me an accurate wiring diagram. Other model years are not showing a separate PWM control device... Its possible the PWM signal is coming directly from the Engine Control Computer to a Solid State fuel pump relay (no way would a normal mechanical relay work, that thing would be clicking crazy...). Have you checked the functioning of the fuel pump relay?
    – zipzit
    Commented Apr 25, 2017 at 16:53
  • Are you sure there is no pressure regulator can on the end of the fuel rail? Its possible the return line hits the tank somewhere besides the top of the fuel pump system.
    – zipzit
    Commented Apr 25, 2017 at 16:58
  • There is absolutely no return line. I know this for a fact cause I have taken the tank down before. I have try out the similar relays and the situation is still the same. So I think its not a problem with the relay. Commented Apr 25, 2017 at 17:36
  • Yeah, but... it there is no separate PWM module, that means the PWM function could be an internal part of your Engine control Computer, and that is expensive. Never mind the fact that you can't simply perform a good part / bad part test... I'm sorry I don't have specific knowledge on your make/model car. I don't know for a fact that the PWM chip is in the computer, but its certainly possible. I'd love to see a real wiring diagram for your car. Do you have a Chilton/Haynes manual? If not, why not?
    – zipzit
    Commented Apr 25, 2017 at 17:43

Yes, although I don't see how a car is going to run with the ECU completely bypassed, I'm guessing you have made some sort of modifications. The ECU is a computer which calculates the right fuel-air mixture for your engine based on sensor date like air temperature, air density, engine operating temperature, exhaust gas temperature, and other factors. If the ECU does not have the information it needs to make that decision then the mixture it chooses will go for a default mix which is likely to work in a large variety of situations, and is often on the rich side. A rich mixture means higher fuel consumption, it also can foul your plugs, ruin a catalytic converter, and cause other problems.

  • What happen was only the ground wire to the pump had current. so I trace the other line to the relay. At first taught it was a relay problem so I replace the relay with other working relays and the situation was still the same. So all I did was find a switch wire and attach it to the relay that is how I have been running the car. So with this high consumption, I thinking that the ECU is being bypass. I try direct current even from the battery and the engine could still start and run. I am really becoming convince that it is an ECU problem. Commented Apr 25, 2017 at 17:48
  • @GregoryDavies What do you mean the ground wire had current? Do you mean continuity? Which relay did you replace? The EFI relay? How was the EFI fuse? Did you check the Circuit Opening relay? On Corollas sold in the US (this may be the same for all markets) the fuel pump circuit is fairly convoluted. Both the EFI and CO relay are used in powering the fuel pump. This includes multiple splices in the harness that powers other things like the ECM.
    – Ben
    Commented Apr 25, 2017 at 21:33
  • Thanks for your concern! Ok, let me put it this way. Two wires go to the fuel pump. The negative(ground) and the positive. I notice that when the switch was turn on the was no sound from the pump. So I check and found that the positive would not produce current when the switch was turn on. I have check all the fuse and relays and they all seem to be working. Commented Apr 25, 2017 at 23:07

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