Free Auto Repair Advice by Certified ASE Technicians
How to Repair a Car
/ How
to Test a Fuel Injector
How to Check a Fuel Injector
READ COMPLETELY BEFORE BEGINNING:
Check for Fuel Injector Malfunction.
When a
fuel injector
malfunctions it can allow excess fuel into the engine. The fuel injector is
manufactured with a control valve that allows fuel to flow at prescribed
amounts. If this valve sticks open it will flood the cylinder with fuel. This
excess fuel causes black smoke from the exhaust system. To test for this
condition the injector fuel rail must be removed and injectors tested. It is
difficult to fully test an injector, but an basic operation test would include
pressurized air and a 12 volt power source. While an engine is running you should be able
to hear the injectors clicking as the electronic valve opens and closes. To
aid in this inspection use a stethoscope and touch it against each injector.
If no audible sound is heard test fuel injector pulse and supply voltage output
(this test is used for most cars).
Fuel Injector
This test will tell you if the computer
system has operating voltage and injector trigger signal. Remove an electrical
connector from a fuel injector (all injectors need to be tested) probe both
sides of the connector with a grounded
test light
or
multimeter (voltmeter) (black lead) switched to DC voltage (there are only
two terminals). Have a helper turn the key to the "on" position without cranking
the engine and observe the test light. The
test light
should illuminate one side of the connector only and the multimeter should be
at about 12 volts. Next, switch the test light or
multimeter (voltmeter) lead (black) or to the positive side of the battery
to test the system ground injector trigger, probe the side of the connector
that did not light up, have a helper crank the engine over and observe the test
light, it should blink on and off or the
multimeter (voltmeter) should bounce from 0 to 12 volts. (Note: if
no injector pulse is present try disconnecting the remainder of injectors and
re-test, if a fuel injector is shorted it can shut down the injector driver
causing no injector pulse. If injector pulse returns plug the injectors electrical
connectors in one at a time until the pulse fails and then replace that injector).
If this test revealed that there was no pulse but system has power, the ECM is
not generating a fuel injector trigger. If there is no trigger to the fuel injector
it will not allow fuel to enter into the engine. Some of the most common reasons
that can cause this condition include a shorted fuel injector, injector wiring
damage or shorted ECM/PCM. While the injector trigger wire is off, test the fuel
injector windings by setting the
multimeter (voltmeter) to ohms and attach the leads to either side of the
injector. Your reading should be between 11 and 18 ohms. Test all of your injectors;
if one injector reading is considerably different from the others replace
that injector. Check the fuel pressure regulator, remove the vacuum line
feeding the fuel pressure regulator, check for the presence of fuel, if fuel
is present the diaphragm inside the regulator has ruptured and is feeding
raw fuel into the engine causing it to run rough.
Common Problems:
- A fuel inject is subject to high temperatures that can cause the inject
to short circuit. Each injector has a specific ohms of resistance reading
that can be tested. This ohms reading can be found in a
car repair
manual. Temperature will cause readings to vary slightly. Injectors
should be tested hot and cold. This is necessary because the heat or cold
can create a condition that can short circuit the injector.
- Moisture can cause the injector connection to short circuit. Always
inspect and clean all electrical connections at the fuel injector,
How to Repair a Car
/ How to
Test a Fuel Injector
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