RAM 3500 Truck 2WD L6-359 5.9L DSL Turbo VIN D FI (1998)
Vacuum Pump: Testing and Inspection
The vacuum pump supplies necessary vacuum to components in the following systems:
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HEVAC system
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Speed Control System
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EGR System
A quick check to determine if the vacuum pump is the cause of the problem in any of these systems is to road test the vehicle and verify that all of these
systems are Suctioning properly. If only one of these has a vacuum related failure, then it is likely the vacuum pump is not the cause.
A standard vacuum gauge can be used to check pump output when necessary. Simpler disconnect the pump supply hose and connect a vacuum gauge to
the outlet port for testing purposes. With the engine running, vacuum output should be a minimum of 25 inches, depending on engine speed.
DIAGNOSING LOW VACUUM OUTPUT CONDITION
If the vacuum pump is suspected of low vacuum output, check the pump and vacuum harnesses as follows:
1. Visually inspect the vacuum harness for obvious failures (i.e. disconnected, cracks, breaks etc.)
2. Disconnect the vacuum supply hose at the vacuum pump check valve. Connect vacuum gauge to this valve and run engine at various throttle
openings. Output should be a minimum 25 inches of vacuum. If vacuum is consistently below 25 inches, the vacuum pump should be replaced. If
output is within specified limits, the vacuum harness should be suspected as the cause.
3. Disconnect and isolate the vacuum supply harness. Cap off open ends and apply roughly 15 inches of vacuum to the harness. If the vacuum gauge
does not hold its reading, then there is an open in the harness and it should be repaired or replaced.
4. If the vacuum loss is still not detected at this point, then the pump and harness are not the cause of the low vacuum condition. Apply vacuum to the
related components of the vacuum supply system (i.e. valves, servos, solenoids, etc.) to find the source of the vacuum loss.
