Chapter 6 Emissions control systems 6-19
kr control valve
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Lead valve
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Low land
Carburetor primary
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13.1 Feedback carburetor
system schematic
NOTE: C Carburetor control unit
+ Battqy
.
13.15 The carburetor fasteners must be
checked to make sure they’re tight or
air/fuel leaks will occur
3 The jet mixture solenoid, which is controlled by the ECU, is used to
enrich the mixture if the exhaust gas oxygen sensor detects a lean condi-
ition. As the mixture is restored to optimum, the jet mixture solenoid re-
sponds appropriately.
4 The enrichment system solenoid is activated in response to in-
creased demand for rich fuel/air mixtures, such as during heave accelera-
tipn or engine loads, cold start and warm-up operation. it provides
additional fuel for the main metering system.
5 The fuel cut-off system deceleration solenoid cuts off fuel flow when
the ignition key is turned off to prevent engine run-on (dieseling). Under
certain deceleration conditions, the solenoid valve reduces fuel flow to de-
crease HC emissions and improve fuel economy.
6 Sincethefeedbackcarburetorisrathercomplex, majortroubleshoot-
ing and testing of the system should be left to a dealer service department.
However,thedo-it-yourselfercanperformmanyofthemaintenancechecks
andtestingprocedureswithoutspecialequipment.Symptomsofaproblem
in the FBCinclude hardstartingorfailure tostart, unstableidleandpoordri-
veability.Ifaproblemoccurs,besuretochecktheignitionsystemandengine
mechanical condition before assuming that the FBC is at fault.
Throttle position system check
8 Check the sensor body and plunger for damage and cracks. +
9 Checkthethrottlesensormountingscrewstomakesuretheyaretight
(do not move the sensor or the fuel/air mixture will be adversely affected).
10 The sensor can be adjusted, but it should be done by a dealer service
department (a digital voltmeter is required).
Solenoid va/ve/thermo valve air filter replacement
11 If the filters on the therm0 valve and solenoid valve are clogged,drive-
ability problems will result.
12 Thethermovalvehasacapwhichfitsoverthefilter.Ifthecapisremoved
by pulling out on it, the filter can be removed and a new one installed.
13 The solenoid valve filter is aone piece assembly which can be pulled
off the valve and replaced with a new one.
Carbure for fastener check
Refer to illustration 13.15
14 To avoid mixture control problems resulting from air and fuel leaks,
the carburetor fasteners must be checked and tightened at the recom-
mended intervals.
15 Remove the air cleanerassemblvand use awrench, socket orscrew-
7 Remove the air cleaner from the engine and check the throttle posi- driver to check the tightness of the carburetor-to-intake manifold bolts, the
tion sensor plunger operation. Operate the throttle lever and see’if the float chamber cover screws and the accelerator pump mounting screws
plunger follows the cam mounted on the throttle shaft.
(see illustration).
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