B Series Truck L4-2184cc 2.2L 2200 (1988)
Air/Fuel Mixture: Adjustments
Before adjusting idle speed or mixture, be sure the ignition timing, spark plugs, and carburetor float level are all in normal operating condition. Turn off
all lights and other unnecessary electrical loads. Check that all vacuum hoses are properly routed according to vacuum diagram. All adjustments must be
made with the cooling fan motor not operating.
INSPECTION
1.
With engine already at normal operating temperature, start engine and run at 2,000 rpm for 1 minute, then let idle.
Fig. 22 Connecting Dwellmeter To A/F Check Connector.
2.
Connect a dwellmeter to the A/F check connector (Br/Y wire). Set meter to 4 cyl. scale.
Fig. 8 Idle Mixture Dwell Reading Range.
3.
Check the air/fuel solenoid duty cycle (dwell) at the specified rpm (800-850 rpm). Dwell should be in the inspection range and varying.
20° - 70°
NOTE: Adjustment of the idle mixture is normally unnecessary. If the duty cycle is not within specifications, perform the following quick check.
DWELL FIXED BELOW 20° (RICH COMMAND)
The ECU is signaling the mixture control solenoid to "go rich" (engine is idling lean). Try choking the carburetor by covering the air inlet with
your hand, fingers slightly open. Gradually close the air gap between your fingers while watching the mixture control dwell. If the dwell increases,
check for vacuum leaks at carburetor base and intake manifold. Check float level through sight glass and adjust if necessary. If no problems are
found, proceed with idle mixture adjustment. If the dwell does not change while choking the carburetor, check the oxygen sensor and feedback
system.
DWELL FIXED ABOVE 70° (LEAN COMMAND)
The ECU is signaling the mixture control solenoid to "go lean" (engine is idling rich or oxygen sensor is contaminated). Try creating a vacuum
leak by removing the PCV valve and covering the hose with your thumb. Then gradually uncover the hose while watching the mixture control