Cummins/Onan — Gasoline Fuel Pump Test
Testing & diagnosis · Pulsating-diaphragm fuel pump
From a Cummins/Onan service manual covering: P216, P218, P220, P248. Check it applies to your exact model before use.
Applies to: Cummins/Onan P216, Cummins/Onan P218, Cummins/Onan P220, Cummins/Onan P248
Before you start
- Ignition of fuel can result in severe personal injury or death. Thoroughly clean up any spilled fuel. Do not smoke or allow any source of ignition near the work area.
Procedure
- Operate the engine at idle for five minutes to ensure the carburetor is full of fuel.
- Shut the engine off and remove the fuel inlet line from the fuel pump.
- Connect a vacuum gauge to the pump inlet using a piece of fuel hose with clamps.
- Start the engine and idle for at least five seconds; record the vacuum gauge reading.
- Move the throttle to high idle position, wait at least five seconds, and record the vacuum reading.
- Shut off the engine, remove the vacuum gauge hose, and connect the fuel inlet line.
- Remove the fuel outlet line and connect a pressure gauge using fuel hose with clamps.
- Start the engine and idle at least five seconds; hold the pressure gauge level with the pump outlet and record the reading.
- Move the throttle to high idle, wait five seconds, and record the pressure reading.
- Remove the pressure gauge hose and reconnect the fuel outlet line. Replace the pump if readings are not within Table 7-1.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Pump inlet vacuum (minimum) 2.6 inches of mercury at low idle and high idle
- Pump outlet pressure (minimum) 1.7 psi at low idle and high idle
Full service-parts list: Cummins/Onan P216 →, Cummins/Onan P218 →, Cummins/Onan P220 →, Cummins/Onan P248 →
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.