Your car's fuel pump is used to supply gas to the engine's fuel
injectors weather it be gasoline or diesel fuels. Depending on the fuel system
design you can have one or more styles of pumps in various locations both
mechanical and electric models. Direct injection fuel systems can be both diesel
and regular gasoline which is comprised of a primary pump in the fuel tank and a
secondary "high pressure" pump which mounts and is driven by the engine. Regular
pressure fuel injection system have just one main pump in the fuel tank. A fuel
pump test will show the performance condition of the pump.
Can cause low power, hesitation and no start conditions
Is controlled by an electric relay or the revolution of the engine
Needs an external gauge to check pump performance
Is between two and three hour job to replace (most cases)
Secondary or "high pressure pump" is mounted to the engine
What's the cost?
Most people do not have a fuel pump test kit but fear not, auto parts
stores will lend you one for free in most cases. If you suspect the fuel pump is
getting weak in your car and you take your car to a shop to have the test done
you can expect to pay between $90.00 and $150.00 US.
Let's Get Started
Begin with the vehicle on flat ground in park with the emergency brake set,
engine off (no smoking or open flame). This test is for in-tank fuel pumps only.
Pressure Port: Some cars are designed with a convenient pressure port on
the engine fuel rail (remove cap) to attach the gauge to while other designs
will need an adapter from the test kit which can be attached at the fuel
filter or fuel pressure feed line headed to the engine's fuel rail.
Remove the fuel pressure test gauge from the kit. Most gauges have a
quick disconnect coupler that will allow several different adaptors for
various manufacturers. The kit should have them labeled but if not look for
the hose connector or fitting that will work for your car.
When attaching the pressure gauge (engine off) a small amount of fuel
may be present so don't be alarmed have a shop towel ready.
Without starting the engine turn the ignition key to the on position the
gauge should jump up to between 45 psi and 58 psi (DPI) direct port injection systems, throttle body injection
(TBI) should be between 13 and 17 psi in most cases as the system primes. If no
pressure is present recheck the hose or adapter connection to avoid any
false negatives, re-cycle the ignition switch to recheck. Still no pressure?
suspect a bad fuel pump, fuel pump relay or fuse.
Now start the engine so we can test the performance of the pump. While
the engine is running, the fuel pressure should drop about 5 psi, from the
static prime pressure (DPI) then snap the throttle, the
fuel system pressure should jump up about 5 psi. this means the fuel pump and pressure regulator
is working correctly. If the system fuel pressure does not respond inspect the
feed line and if okay the fuel pressure regulator has failed (if equipped).
The final check will be the load test. This test will determine how the
pump performs under load of use. This can be achieved by one of two ways,
first you can load the engine by having the transmission in reverse
(automatic) and hold the brake while gently giving the engine a slight
amount of throttle. This will load the engine while not allowing the car to
move effectively loading the engine and fuel pump. The second way is to
close the hood to the first safety catch and drive the car (not at highway
speeds) while the gauge rests outside being visible to the driver. The hose
will route from the side of the hood while using masking tape to secure the
gauge. The pressure should hold continuously throughout the test. If the
fuel pressure is low under load or while idling the
fuel filter (if
equipped) could be clogged, or the
fuel pump has failed
and needs replacement.
Remove the fuel pressure gauge and reinstall the dust cap or remove the
fuel line adaptor clean up any excess fuel.