Actron AutoTroubleShooter CP7677 - 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
electronically 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 test the fuel
mixture control solenoid on Gen-
eral Motors vehicles and to mea-
sure fuel injector resistance.
Testing GM C-3 Mixture Control Solenoid Dwell
This solenoid is located in the carbure-
tor. Its purpose is to maintain an air/fuel
ratio of 14.7 to 1 in order to reduce
emissions. This test checks to see if the
solenoid dwell is varying.
Test Description:
This test is rather long and detailed. Refer
to vehicle service manual for the com-
plete test procedure. Some important test
procedure highlights you need to pay
close attention to are listed below.
1. Make sure engine is at operating
temperature and running during
test.
2. Refer to vehicle service manual
for multimeter hook-up instruc-
tions.
3. Turn multimeter rotary switch to 6
Cylinder Dwell position for all GM
vehicles.
4. Run engine at 3000 RPM.
5. Make engine run both RICH and
LEAN.
6. Watch multimeter display.
7. Multimeter display should vary
from 10
°
to 50
°
as vehicle changes
from lean to rich.
Typical Mixture Control
Solenoid Connection
Mixture Control
Solenoid