Transfer Pump Restriction
Figure 1. Diagnostic Form
Follow these steps to check for a restriction in the transfer pump. For a reproduction of the applicable portion of the diagnostic form, see Figure
The purpose of this test procedure is to determine if low fuel pressure is caused by excessive restriction in the fuel supply line from the fuel tank(s) to the transfer pump inlet.
Follow this procedure to check for a restriction:
- Connect a tee between the fuel filter inlet and the fuel supply line. Connect a line from the tee to the 0–30 in. Hg. vacuum gage of the Pressure Test Kit.
- Measure fuel inlet restriction at high idle and record the reading on the diagnostic form.
- If the restriction exceeds 8 in. Hg, locate the restriction on the suction side of the fuel system and correct. If the restriction is within specifications or very low, perform the following:
- Remove the fuel supply line; connect a clear plastic line to the fuel inlet fitting; and connect the fuel supply line to clear the plastic line.
- Check for air bubbles in the clear plastic line while the engine is running at high idle. If air bubbles are visible, inspect the fuel system for suction leak(s) and repair. If air bubbles were not present in the clear line, remove the clear plastic line.
- Install a plug to seal off the fuel inlet. Start the engine and run at high idle. Vacuum reading should be greater than 22 in. Hg. If less, check for air ingestion from the vacuum gage to the transfer pump. If no leak is found, replace the transfer pump.
Note: If no leaks are found on the inlet side of the fuel system, and the transfer pump is providing > 22 in. Hg vacuum, replace the fuel return valve. Check the fuel pressure again to verify the valve was defective.
Possible causes for a transfer pump restriction include:
- A fuel filter could cause high restriction and low fuel pressure because of dirt or fuel jelling in cold ambient temperatures. Change filter and test again.
- Primary fuel filter or fuel/water separator clogged.
- A kinked or severely bent fuel supply line or blockage at the pickup tube could cause restriction and therefore low fuel pressure.
- A loose fuel line on the suction side of the fuel system could cause air to be ingested into the system and cause low fuel pressure.
- Primary fuel filter or fuel/water separator may be ingesting air into fuel system via loose connections, etc.
- Fuel return valve defective or stuck open due to debris.
- Defective fuel transfer pump.
Engine Field Test Kit J 39257
, tee or reworked hollow screw fitting, NPT pipe adaptor, and appropriate fuel lines.
|Series 40E Troubleshooting Manual – 6SE241
|Generated on 10-13-2008