Pressure Regulator/Converter Inspection Visually inspect the pressure regulator/converter (B) housing for coolant leaks. Refer to Chapter 6 if the pressure regulator/converter requires replacement. Fuel Trim Valve Inspection (FTV) Visually inspect the fuel trim valves (C) for abrasions or cracking. Replace as necessary. To ensure a valve is not leaking a blow-by test can be performed. 1. With the engine off, disconnect the electrical connector to the FTVs. 2. Disconnect the vacuum line from the FTVs to the pressure regulator/converter at the converter’s tee connection. 3. Lightly blow through the vacuum line connected to the FTVs. Air should not pass through the FTVs when de- energized.
If air leaks past the FTVs when de-energized, replace the FTVs. Inspect Air/Fuel Valve Mixer Assembly Refer to Chapter 6 for procedures regarding the LP mixer (D). Inspect for Intake Leaks Visually inspect the intake throttle assembly (E), and intake manifold for looseness and leaks. Repair as necessary. Inspect Throttle Assembly Visually inspect the throttle assembly motor housing for coking, cracks, and missing cover- retaining clips. Repair and/or replace as necessary. NOTE: Refer to Chapter 6 for procedures on removing the mixer and inspecting the throttle plate.
Checking the TMAP Sensor(G643E only) Verify that the TMAP sensor (F) is mounted tightly into the manifold or manifold adapter (E), with no leakage. If the TMAP is found to be loose, remove the TMAP retaining screw and the TMAP sensor from the manifold adapter. Visually inspect the TMAP O-ring seal for damage. Replace as necessary. Apply a thin coat of an approved silicon lubricant to the TMAP O-ring seal. Re-install the TMAP sensor into the manifold or manifold adapter and securely tighten the retaining screw. Exhaust System Maintenance Inspect Engine for Exhaust Leaks Start the engine and allow it to reach operating temperatures.
Perform visual inspection of exhaust system from the engine all the way to the tailpipe. Any leaks, even after the post-catalyst oxygen sensor, can cause the sensor output to be effected (due to exhaust pulsation entraining air upstream). Repair any/all leaks found. Ensure the length from the post-catalyst sensor to tailpipe is the same as original factory. Ensure that wire routing for the oxygen sensors is still keeping wires away from the exhaust system. Visually inspect the oxygen sensors to detect any damage.(G643E only) G643(E) Service Manual Chapter 2. Recommended Maintenance 28