Cummins/Onan — Check Inlet Air Restriction
Testing & diagnosis · Air intake system
From a Cummins/Onan service manual covering: V12 Series, V6-140, V6-200, V6-VAL, V6-VIM, V8-185, V8-265, V8-350, V8-VALE, V8-VINE, VT12, VT8-430. Check it applies to your exact model before use.
Applies to: Cummins/Onan V12 Series
Procedure
- On naturally aspirated engines attach vacuum gauge or water manometer in middle of intake manifold.
- On turbocharged/supercharged engines attach checking fixture one pipe diameter upstream of supercharger/turbocharger.
- Idle engine until normal operating temperature is reached.
- Operate engine at rated speed, full load and take reading.
- If air restriction exceeds 25 inches of water or 1.8 inches of mercury, clean or replace element, replace damaged piping, remove excessive bends.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Maximum 25 inches of water or 1.8 inches of mercury at engine; 20 inches of water or 1.5 inches of mercury at cleaner
Full service-parts list: Cummins/Onan V12 Series →
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.