Car Repair Advice by Professional Automotive Experts
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 or no 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. If the
valve sticks closed no fuel is allowed into the engine cylinder. Excess fuel
causes black smoke from the exhaust. On the flip
side if the injector is stuck closed the absence of fuel will cause the cylinder
to go lean effectively fooling the oxygen sensor and causing the system to allow
too much fuel into the engine through the remaining fuel injectors. Injectors
can malfunction at anytime without warning. Using a few basic tests you can
determine if one or more fuel injectors have failed causing the engine
run-ability problem.
Fuel Injector
- While an engine is running you should be able
to hear each injector clicking as the electronic valve opens and closes. To
aid in this inspection use a stethoscope and touch it against each injector.
- Remove the injector electrical connector, turn the key to the on
position without starting the engine.
This test will tell you if the computer
has proper system voltage and injector trigger signal. Remove an electrical
connector from a fuel injector. Probe both
sides of the connector with a grounded
test light
or
multimeter (voltmeter). Set the voltmeter to DC voltage. Have a helper turn the key to the "on" position without cranking
the engine and observe. The
test light/voltmeter
should illuminate/read one side of the connector. The multimeter should read 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. Disable the ignition system so
the engine will not start (disconnect ignition coil or remove the ignition
fuse). Probe the side of the connector
that did not light up in the previous step, 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 in one at a time until the pulse fails.
Replace effecting injector). If this test is positive and the injector still
will not operate the injector has failed and replacement is required.
- While the injector wire connector 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 will vary depending on manufacturer. For the exact
ohms reading a
car repair
manual is needed. Test all of your injectors; if one injector reading is
considerably different from the others replace the different 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.
NOTE:
If this test revealed no injector pulse but system has power, the PCM is
not generating a fuel injector trigger. If there is no trigger the fuel injector
it will not allow fuel to enter into the engine. Some of the most common reasons
are a shorted fuel injector, injector wiring
damage or shorted PCM driver.
Common Problems:
- A fuel injector is subject to high temperatures that can cause the injector
to short circuit. Each injector has 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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