Actron AutoAnalyzer CP7665 - Manual (Page 25)

25
Fuel System Testing
The requirements for lower vehicle emissions has increased the need for
more precise engine fuel control. Auto manufacturers began using elec-
tronically controlled carburetors in 1980 to meet emission requirements.
Today’s modern vehicles use electronic fuel injection to precisely control
fuel and further lower emissions. The digital multimeter can be used to
measure fuel injector resistance.
Measuring Fuel Injector Resistance
Fuel injectors are similar to sole-
noids. They contain a coil that is
switched ON and OFF by the ve-
hicle computer. This test measures
the resistance of this coil to make
sure it is not an open circuit. Shorted
coils can also be detected if the
specific manufacturer resistance of
the fuel injector is known.
Test Procedure (see Fig. 26):
Fig. 26
Typical
Fuel Injector
Black Red
1. Insert BLACK test lead into
COM test lead jack.
2. Insert RED test lead into
test lead jack.
3. Turn multimeter rotary switch
to 200
Ω
range.
Touch RED and BLACK multim-
eter leads together and view
reading on display.
Display should read typically 0.2 -
1.5
Ω
.
If display reading was greater
than 1.5
Ω
, check both ends of
test leads for bad connections. If
bad connections are found, re-
place test leads.
4. Disconnect wiring harness
from fuel injector - Refer to
vehicle service manual for pro-
cedure.
5. Connect RED and BLACK
test leads across fuel in-
jector pins.
Make sure you connect test
leads across fuel injector
and not the wiring harness.
6. Turn multimeter rotary
switch to desired OHM
range.
If the approximate resis-
tance is unknown, start at
the largest OHM range and
decrease to the appropri-
ate range as required. (see Set-
ting the Range on page 6)
7. View reading on display - Note
range setting for correct units.
• If display reading is 10
Ω
or
less, subtract test lead resis-
tance found in Step 3 from
above reading.
• Compare reading to manufac-
turers specifications for fuel in-
jector coil resistance.