A fuel injector is responsible for allowing fuel into the engine and is
controlled by the PCM as part of the
fuel injection system.
Fuel pressure supplied by the fuel pump is metered by the duty cycle of the
computer which varies by engine load. This guide will show you how to check the trigger (ground) signal from the PCM, power circuit and the
operation of the injector itself. To test the injector signal from the computer a test light
works best. You will need a voltmeter to check resistance through the injector.
Fuel maybe present during testing so the usual fire precautions are necessary.
Use protective gloves and eye wear for safety. Test for FI systems only.
Test the coil windings resistance using a volt meter
Confirm injector valve operation
Inspect the injector casing for leaks
Check flow and spray pattern
Let's Get Started
Start the engine and allow it to idle. Using a long metal rod like a screwdriver touch the end of the screwdriver to the injector.
Gently lay an ear to the opposite end of the rod or handle to observe an audible clicking sound to confirm the injector is working.
Injector Circuit Power Test
With the key in the on position use a
test light or
voltmeter connected to the
negative side of the battery. Gently probe both sides of the injector wiring
connector, one of the wires should react by registering around 12 volts on
the meter or illuminating the test light. If neither wire reacts test the
fuel injector fuse in the PDC. If the fuse is okay a fuel injection wiring
diagram is needed to help trace the
wire and repair the connection. Seal test points with a small dab of
silicone rubber once testing is complete.
Injector Ground Trigger Test
closes the injector circuit to trigger the injector operation. For this a test light works best to observe the pulse
produced by the PCM. Attach the test
light lead to the positive side of the battery and have a helper start or
crank the engine. Probe the opposite side of the injector connector from the
power circuit, you should observe the test light flicking which will respond
to engine RPM/Load. If the engine is running and no pulse is observed suspect a
bad wiring connection or a failed PCM injector driver which will warrant a PCM
replacement. A shorted injector can hinder the injector driver operation for
additional injectors, unplug all injectors and re-test the signal. If
pulse returns plug the injectors back in one at a time until the pulse
fails then replace the shorted injector. If the
engine is not running check the
sensor which the computer uses to open the injectors (Note: A failed
crankshaft angle sensor will not set a trouble code in most cases).
Fuel Injector Winding Test (key off)
Using a voltmeter, adjust the setting to ohms. This test can be performed with the injector installed or uninstalled.
Remove the injector electrical connector
This will expose the injector electrical terminals.
Connect the voltmeter leads to the terminals, the polarity of the leads
is irrelevant. This test gives a baseline ohm reading of all injectors, a service manual also has this information.
Most injector readings should range between 11 and 24 ohms. Fuel injectors should be tested cold
unless otherwise specified, temperature variances will change the readings. If the
test shows high resistance or an open circuit the
The valve and spray pattern is the most important part of testing a fuel
injector. Valve testing can be done with the injector still installed using
a fuel pressure gauge while hot wiring the fuel pump to stay on. Carefully
attach a 12 volt power (power and ground) source to the injector, you should
be able to see the gauge fluctuate as you connect and disconnect the circuit
if the injector valve is working and not plugged.
To check the injector spray pattern the injector must be removed. Attach
pressurized air to the injector inlet. Attach a 12 volt power and ground
source to energize the injector. Compressed air should be released from the
outlet valve with traces of fuel still remaining from the injector (use fire
precautions). Observe the pattern which should be robust, if the pattern is
muted the injector should be replaced.