How to check the fuel pump

The causes of gasoline pump failure are not always the same, so the test may be different. Functionality should be diagnosed by the symptoms of work. If the pump does not pump fuel at all and the car does not start, you will need a multimeter or at least a light bulb with a wire.

Common Signs of a Faulty Fuel Pump

The gasoline pump should be checked if there are the following signs of malfunction:

  • engine stalls;
  • the vehicle moves irregularly, jerking;
  • the engine idles unstable, does not start
  • engine hunting;
  • noise, and whistling during driving increases.

How to Properly Test and Diagnose a Bad Fuel Pump

Check the operation of the gasoline pump

How to Diagnose a Failed Car, Truck & SUV Fuel Pump

When turning the ignition key you will hear a slight buzzing, slight humming, that's how the fuel pump works, and creates pressure in the system. If there are no such signs of work when you try to start, then you can assume a malfunction of the electrics, the pump itself or its individual parts.

So let's look at how you can check the operation of the gasoline pump according to a step-by-step logical chain. Starting from whether the pump is receiving power and ending with whether the pump is pumping at all, and if it is, what pressure it creates in the fuel rail.

Step 1: Checking the Fuse

Checking the fuel pump fuse involves inspecting the integrity of the conductive plate and, if broken, replacing it. But if there is no new fuse, then wrap one strand of copper wire around the fuse contacts. It burned out again — then the problem may be in the wiring.

Step 2: Check Relay

To check the gas pump relay, take it out of the socket, connect a 12-volt light bulb according to the diagram. If the light bulb works, the relay itself also works. Alternatively, you can use a multimeter in ohmmeter mode to measure the resistance of the coil winding of the relay. Connect one probe to terminal 85 and the other to 86. The device will indicate an open circuit if the relay has failed.

Make sure the terminals are not oxidized — this will adversely affect electrical power to the fuel pump motor!

Step 3: Checking Power to the fuel pump

Check the voltage of the gasoline pump by using a multimeter. The measuring device probes in voltmeter mode (from 0-20 volts) should be connected to the petrol pump power terminals. Switch on the ignition and take a reading on the device. 12-12.5 volts is a normal working voltage. If there is voltage, but the pump does not work, check the electric motor.

Step 4: Check the gasoline pump motor

To exclude electric motor damage we supply 12 volt directly from the battery to the gasoline pump terminals. If itt works — check its performance, check the return valve, and measure pressure with the manometer. It doesn't work — check the coil for breakage.

If there is a voltage on the gasoline pump terminals it does not work? Let's check the stator winding: take the tester (multimeter), put it in ohmmeter mode, it should show resistance, otherwise, there is a problem with the winding and it must be replaced. If it shows resistance, the problem may be that the winding is shorted to the gasoline pump housing. The tester stylus is on the plus terminal, the other stylus is on the housing. If it is shorted, there will be no breakage.

Step 5: Checking the coarse filter

If you remove the coarse filter (see vehicle datasheet) from the gas pump you can even visually see how dirty it is. One of the signs of problems with the filter can be a decrease in pressure in the fuel rail, it will report the check engine indicator on the panel and error code P0087. A filter change is indicated if there are a lot of deposits, if the problem is on the road use a brush and gasoline to clean it.

A preventive check of the gasoline pump, which includes cleaning the tank, filters and injectors will help save on an expensive device! And use quality fuel!

Step 6: Check the check valve

The check valve must permanently prevent the flow of liquid in the opposite direction. During operation its performance decreases, which reduces the technical characteristics.

1 way. Check the check valve to measure the pressure with a manometer. Connect it to the part of the system, which is directly involved in fuel supply to the engine. The pressure reading should not exceed 3 kg/square cm (it is true for cars). And when you stop the engine, the pressure must not drop sharply.

2-nd way. To check the operation of the gasoline pump check valve without a pressure gauge, you need to squeeze the return and watch how the engine runs. If the check valve is faulty the engine will run at high rpm (provided there are no other problems).

The 3rd way. Combines both diagnostics and cleaning of a check valve at the same time. Remove and inspect it — clogging, which requires cleaning, is visible to the naked eye. You can also blow through the valve with a strong jet of air, but it is better to run water under pressure through it. This way you will combine checking the valve with its cleaning. If the valve still does not work, you need to replace it.

Step 7: Check the pressure

In order for the diagnostics to correctly determine the pressure reading, you need to reset the initial fuel pressure by disconnecting the fuse of the gasoline pump.

How To Diagnose A Fuel Pump Failure

How to test a fuel pump with a pressure gauge

To check the gasoline pump with a pressure gauge for proper operation is as follows: connect the device to the fuel ramp. Output — through the edge of the hood to the windshield, where you set the device securely.

Fix the measurements in:

Static position. Turn the ignition key and look at the gauge reading, it must not exceed 3,7 atm.

Dynamics. Engage the third gear (speed about 50 km/h), watching the data gauge. When driving, if there is a pressure problem, the readings will be either below 3 atm or above 3,7 atm.

Low pressure in the fuel system may be the result of a fuel leak. A fuel leak will show a pressure drop below 1.6 atm. The fault is in the injector or fuel regulator.


  • How do you check if a fuel pump is bad?

    You should perform checks of 5 main elements — fuses, relay, power check, petrol pump motor, and coarse filter.

  • What are the signs you need a new fuel pump?

    You can find out that the fuel pump isn't operating in a proper way by several signs:

    • sputter, surge of an engine;
    • power decrease under load;
    • troubles when starting the engine;
    • from the fuel tank is coming a whining noise;
    • reduced fuel consumption;
    • engine stalls at high temperatures.
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