Air Intake Restriction Gauge

An intake-air restriction indicator, mounted in the engine compartment, measures the vacuum on the engine side of the air cleaner at the air cleaner outlet. See figure and figure .

Air intake restriction vacuum is measured in inches of water (inH ²O). For vehicles equipped with a graduated indicator or a restriction gauge on the dash, check the gauge with the engine off. If restriction reaches 25 inH ²O, for Cummins diesel engines, or when the air restriction indicator is completely red for gasoline and Detroit™ diesel engines (if equipped with an air restriction indicator), replace the air cleaner element. Reset the indicator by pushing it down.

Fig. 1, Air Intake Restriction Gauge, Cummins Diesel Engines

Partial Restriction

Full Restriction

Fig. 2, Air Restriction Indicator, Gasoline and Detroit Diesel Engines