Air Restriction Gauge
The air intake restriction gauge measures the vacuum on the engine side of the air cleaner. On standard installations, it is mounted on the air intake duct in the engine compartment. See Fig..
As an option for easier viewing, an air intake restriction gauge may be located under the lightbar. See Fig..
Fig. 1, Air Intake Restriction Indicator, Graduated
Fig. 2, Air Intake Restriction Gauge
Note: Rain or snow can wet the air filter, causing a temporarily higher than normal reading.
Air intake restriction vacuum is measured in inches of water (inH2O). For vehicles equipped with a graduated indicator or a restriction gauge on the dash, check the gauge with the engine off. If the air restriction value equals or exceeds the value shown in Table., the air cleaner element needs to be replaced.
Table 1, Air Intake Maximum Restriction Values
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Air Intake Maximum Restriction Values (inH2O) |
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Engine Make |
GHG14, GHG17, and GHG21 Engines |
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Detroit |
18 |
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Cummins |
25 |
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