Restricted Exhaust System Check (chart b1) GMC Cab & Chassis R2500

CHART B1 - RESTRICTED EXHAUST SYSTEM CHECKS

Note. Proper diagnosis of restricted exhaust system is essential before any components are replaced.

1. Remove the rubber hose from the exhaust manifold AIR pipe check valve.
2. Connect fuel pump pressure gauge to hose and nipple from Propane Enrichment Device (J26911).
3. Insert nipple into exhaust manifold AIR pipe.
4. With engine at normal operating temperature and running at 2500 RPM, observe exhaust system backpressure on gauge.
5. If backpressure exceeds 2 3/4 psi, a restricted exhaust system is indicated.
6. Inspect entire system for collapsed pipe, heat stress or possible internal muffler failure.
7. If there is no obvious reasons for excessive backpressure, a restricted catalytic converter should be suspected and replaced.

RESTRICTED EXHAUST CHECK 2 (ALL WITHOUT AIR OR PULSAIR)

1. With engine at normal operating temperature, connect a vacuum gauge to any convenient vacuum port in intake manifold.
2. Disconnect EGR solenoid electrical connector or connect EGR valve directly to vacuum source, by-passing any switches or solenoids.
3. Run engine at 1000 RPM and record vacuum reading.
4. Increase RPM slowly to 2500 RPM and note vacuum reading.
5. If vacuum reading at 2500 RPM decreases more than 3 in. Hg from reading at 1000 RPM, inspect exhaust system for restrictions.
6. Disconnect exhaust pipe from engine and repeat steps 3) and 4). If vacuum reading still drops more than 3 in. Hg with exhaust disconnected, check valve timing.