Service manual

G420F(FE) Service Manual 275 Chapter 8. Basic Troubleshooting
Diagnostic Aids for Rich / Lean Operation
SERVICE TOOL ITEM RICH LEAN
Pre-catalyst O2 A/ D counts Consistently > 250 Consistently < 170
Pre-catalyst O2 sensor switching
between high and low
Always high ADC Always low ADC
Trim valve duty cycle > 90% < 10%
Fuel injector pulse width at idle * < 1.0 msec > 8 msec.
Malfunction codes • Pre-catalyst O2 sensor failed rich
• Pre-catalyst O2 sensor failed
lean
Closed loop operation • Pre-catalyst O2 sensor high • Pre-catalyst O2 sensor low
(*) The duty cycle injector pulse width criteria for lean or rich operation apply only if the O2 sensor is
functioning properly. If the sensor is not operating properly the criteria may be reversed.
Rich Operation
LP (Trim valve duty cycle>90%)
• Inspect hoses from AVV port (port on bottom of
mixer) to trim valves and regulator for leaks or
blockages, replace as necessary.
• Inspect in-line orifices for blockages (in wye),
replace as necessary
• Check trim valves for proper operation, replace as
necessary
• Check regulator out pressure, replace if out of
spec
• Inspect fuel cone for damage, replace mixer
assembly as necessary Gasoline (Injector Pulse
Width<1.0 msec)
• Check gasoline fuel pressure
• Check injectors for sticking, replace as necessary
Lean Operation
LP (Trim valve duty cycle<10%)
• Check for vacuum leaks, replace hoses, o-rings,
and gaskets as necessary
• Check balance line for blockage, replace as
necessary
• Check vapor hose for restrictions, replace as
necessary
• Check trim valves for proper operation, replace as
necessary
• Check regulator out pressure, replace if out of
spec
Gasoline (Injector Pulse Width>8 msec)
• Check system voltage
• Check fuel pressure
• Check injectors for sticking or obstructions