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Page 52
Introduced in 1978 on a limited number of California mandated emission-
controlled engines, the C-4 System is now standard equipment on most of
the Genera] Motors cars (except diesel and EFI).
The main functlon_of the
C-4 System is to maintain the carburetor air-fuel ratio at 14.7 to 1.0--the
most efficient operating ratio for the catalytic converter.
The electronic
carburetor receives a DWELL-TYPE voltage from the EleCtronic Control Module
(ECM) to maintain this air-fuel ratio under widely varying driving
conditions. The Craftsman Engine Analyzer can be used to check this
voltage by reading the six-cylinder DWELL scale, 0-60°, and by performing
the procedure in this section.
IMPORTANT--The C-4 System could be malfunctioning when any of the following
conditions are noticed:
The vehicle instrument panel "CHECK ENGINE" light illuminates.
Poor engine performance which includes=
1.
Poor gas mileage
2.
Lack of response to throttle
3.
Hesitation, stalling, etc.
Complete C-4 System diagnostics, troubleshooting, and repair procedures
demand that you obtain the specific service manual f_r your vehicle and
engine combination.
CONNECTIONS:
On G.M. cars equipped with the C-4 System, a small, green, single-contact
DWELLMETER connector is normally provided to check the DWELL voltage to
the carburetor (usually located under the hood near the right front
fender wheel well, or near the carburetor, protruding from the wiring
harness). DO NOT ALLOW THE LEADS TO TOUCH GROUND OR HOSES--THE HOSES MAY
ALSO BE CONDUCTIVE.
Use the adapter pin as shown in the figure below.
Connect the GREEN clip
from the Craftsman Engine Analyzer to the adapter pin.
Connect the
BLACK clip to a clean and secure ground such as the engine block, and the
RED clip to the positive (+) battery terminal.
NOTE:
The DWELLMETER should NOT cause a change in the engine operation
when connected to the vehicle's DWELLMETER connector.
If there is reason
to suspect that a change did occur, recheck your connections.
TEST PROCEDURE
Position the FUNCTION SELECTOR switch on the Craftsman Engine Analyzer
in the DWELL position.
All readings will be taken from the 6-cylinder
DWELL scale (0-60°), regardless of the number of engine cylinders in the
vehicle under test.
The following table is a typical C-4 System Performance Summary illustrating
the DWELLMETER readings under the given engine conditions.
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