measurement. The MC solenoid’s purpose is to
maintain an air/fuel ratio of 14.7 to 1.
This test can verify if the solenoid dwell is varying as
designed. This test is very detailed and you need to
pay close attention to the shop manual instructions.
Visit this web address http://s7d9.scene7.com/is/
content/GenuinePartsCompany/1787689pdf?$P
DF$ or use a shop manual for the complete test
procedures for adjusting a Lean/Rich fuel mixtures.
Refer to vehicle service manual for the specific
meter test connection points.
1. The engine needs to be running and at normal
operating temperature.
2. Turn the meters range selector to the 6 cyl.
Dwell position for all GM vehicles with MC solenoids.
3. The engine idle needs to be at 3000 RPM.
Use the reference web site, or shop manual for the
procedure to run the engine both RICH and LEAN.
View the meter display, the Dwell values should vary
from 10° to 50° as vehicle runs from rich to lean.
Measuring Fuel Injector Resistance
Fuel injectors are basically an ON/OFF switch.
Very similar to solenoids, they contain a coil that is
controlled by the ECU. If your engine is running
rough, there may be an issue with the vehicle’s fuel
delivery system. Having a faulty injector can cause
one or more cylinders to not ignite fully. The ECU
directs the injector to deliver precise amounts of fuel
into each cylinder, regardless of the engines RPMs.
An injector fires millions of times over its life span.
Eventually they can wear out or clog up, preventing
the engine from firing properly. To determine if the
injector is operating properly the resistance of the
internal coil is tested. Testing this resistance reading
will advise if you have an open circuit, or if the coil
is shorted. Its best if you have the specific injector
manufactures rated resistance. Some of the more
common manufacturers of fuel injectors are Bosch,
Siemens, Deka, Continental, Lucas, Japanese
Electronics Corp. (JECS), and Denso.
Injector Test
Some engines have plastic panels that need to be
removed before you can access the injectors. They
are typically secured by bolts and can be removed
with a basic socket set including an extension.
1. Testing the Injector, make sure the key is off, no
power is needed for this test.
2. Remove the injector wiring harness. Be cautious,
the harness has slide lock that you need to move
before you can press on the tabs to remove the
wiring harness.
3. Insert BLACK test lead into COM test lead jack.
FUEL SYSTEM TESTS
4. Insert RED test lead into test lead jack.
5. Turn the meters range selector to the 200Ω setting.
Because of the sensitivity of this test touch the two
probes of the test leads together. View the reading on
the display and record the resistance value.
6. Add the alligator clips and connect the RED
clip to a single prong inside the injector’s connector.
7. Connect the BLACK clip to the other prong, be
sure the two clips don’t touch.
8. View the reading on the display, subtract the test
lead resistance value from above. Record this final
figure.
9. Repeat the above steps for each injector and
record the results. They should all have a resistance
within half an ohm from each other. Any major
difference and that injector should be inspected to
make sure its firing correctly. If the resistance of the
injector coil is within manufacturer’s specifications,
the fuel injector could still be defective. It is possible
that the fuel injector is clogged or dirty and that is
causing your drivability problem.
High impedance injectors are the most common on
vehicles today, they will range from 12 to 17 ohms.
Low impedance injectors are found on high
performance and larger injectors. They have much
lower resistance, typically around 2-5 ohms.
• A good Injectors Coil resistance is within
manufacturers specifications.
• A bad Injectors Coil resistance is not within
manufacturers specifications.
Injector Wiring Harness Test
1. Testing the Injectors wiring, turn the key to the
ON position, KOEO.
2. Insert BLACK test lead into COM test lead jack.
3. Insert RED test lead into test lead jack.
4. Turn the meters range selector to the 20VDC
setting.
5. Add the alligator clip to the BLACK test lead
only, clip to a good body ground.
6. Touch the RED test leads probe to a single
prong inside the injectors wiring harness. (Not the
injectors, but the harness that plugs into the
injectors connection). One prong will be the ground
and your meter will read 0 volts. The other prong is
the power source for the injector and should read
around 12 volts.
7. View and record the reading on the display.
8. Leave the ground lead in position and repeat the
above steps for each injectors wiring harness and
record the results. Your results should all be around
12 volts. A lower reading means theres excess
resistance in the injectors wiring somewhere.
• A good Injector Harness voltage is within
manufacturers specifications.
• A bad Injectors Harness voltage is not within
manufacturers specifications.
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