Purpose
To determine if intake or exhaust restriction is causing hard start or no start conditions
NOTE: High intake or exhaust restriction can cause a large amount of black smoke when starting the engine.
Tools
• None
Procedure
1. Inspect the following parts for restriction, damage, or incorrect installation:
• Air filter inlet and duct (could include hood, cowling, etc.)
• Hoses and clamps
• Air filter housing, filter element, and gaskets
• Exhaust pipes
• Chassis mounted CAC and piping
• Air filter restriction indicator or gauge
NOTE: Intake restriction should be below 25 in H 2O. When the filter element reaches maximum allowable
restriction, the yellow indicator will reach the top of window and automatically lock in this position.
2. Record concerns on Diagnostic Form.
Possible Causes
• Air filter element clogged or dirty
• Snow in air filter inlet
• Ice in air filter inlet
• Plastic bags or other foreign material in air filter inlet
• Collapsed air filter
• Collapsed inlet piping or hoses
• On engines recently repaired, rags or cap plugs may have been left in the intake system.
• Tailpipe or muffler may be damaged or collapsed.
• Exhaust restriction (muffler or catalytic converter)
• Restricted or plugged Catalyzed Diesel Particulate Filter (CDPF) – if equipped
