Fuel Pump: Testing and Inspection

If the fuel supply system is not delivering enough fuel, or air is being drawn into the fuel injection system, driveability could be greatly effected or a Cranks But Will Not Run symptom could exist. If other diagnosis indicates, or if the fuel supply system is suspected of not delivering enough fuel or drawing air, it should be tested as follows: Testing and Inspection

PRELIMINARY CHECKS
- Air leaks or restrictions on the suction side of the fuel pump will seriously affect pump output.
- Make certain that there is sufficient fuel in the tank.
- Check for leaks at all fuel connections from the fuel tank to the injection pump.
- Tighten any loose connections.
- With the engine running, check all hoses and lines for flattening or kinks that would restrict the flow of fuel.

LIFT PUMP FLOW CHECK
1. Disconnect the electrical connector for the engine shutoff solenoid at the injection pump.
2. Disconnect the pipe at the lift pump outlet fitting
3. Install a hose at the lift pump outlet fitting and place a 1 liter (0.946 quart) container at the hose to collect fuel.
4. Crank the engine and measure the amount of fuel:

- If more than 0.24 liter (1/2 pint) in 15 seconds, refer to "Lift Pump Pressure Check" in this section.
- If less than 0.24 liter (1/2 pint) in 15 seconds, refer to "Lift Pump Suction Line Check" in this section.

LIFT PUMP SUCTION LINE CHECK
1. Remove the fuel tank cap and repeat the "Lift Pump Flow Check."

- If flow is more than 0.24 liter (1/2 pint) in 13 seconds, replace the defective fuel tank cap and refer to "Lift Pump Pressure Check."
^ If flow is less than 0.24 liter (1/2 pint) in 15 seconds, go to next step.

2. Separate the lift pump suction line from the fuel sender.
3. Connect the suction line to a source of clean fuel, using an additional hose.
4. Repeat the "Lift Pump Flow Check."

- If flow is more than 0.24 liter (1/2 pint) in 15 seconds, remove the fuel sender and check it for restriction.
- if flow is less than 0.24 liter (1/2 pint) in 13 seconds, go to Step 5.

5. Check the lift pump suction line for restriction:

- If restriction exists, repair it and recheck lift pump flow.
- If no restriction exists, replace the lift pump and recheck lift pump flow.

6. Attach the lift pump suction line to the fuel sender.

LIFT PUMP PRESSURE CHECK
1. Install a tee adaptor between the lift pump outlet fitting and outlet pipe.
2. Connect a pressure gauge with a dial indication of 0 to 103 kPa (0 to 15 psi) to the tee adaptor.
3. Run engine and measure fuel pressure.

- if pressure is at least 4 psi or 27 kPa go to Step 4.
- If pressure is less than 4 psi. refer to CHART A-5 before replacing lift pump. Testing and Inspection

4. Remove pressure gauge and tee adaptor.
5. Connect outlet pipe at the lift pump outlet fitting.
6. Clean any fuel spillage.
7. Run the engine to check for fuel leakage.

FUEL SYSTEM AIR LEAK CHECK
1. install a transparent hose between the filter outlet and injection pump inlet.
2. Start and idle the engine, observing the fuel for air bubbles.

- If air bubbles are not present, stop the engine and go to Step 6.
- If air bubbles are present, stop the engine and go to Step 3

3. Check the lift pump suction line for air leakage:

- Disconnect the fuel pipe from the fuel sender and plug it.
- Disconnect the fuel pipe from the lift pump, and install a hand held vacuum pump with gauge.
- Apply vacuum to the fuel pipe and observe the gauge reading:

- If vacuum does not drop, connect fuel pipe and go to Step 4.
- If vacuum drops, repair the air leak in the suction line and install the suction line pipe and hose.

4. Check the fuel sender for air leakage:

- Remove the fuel tank.
- Remove the fuel sender from the fuel tank, remove strainer and plug the bottom end of the pickup tube.
- Apply a vacuum to the upper end of the pickup tube, and observe the gauge reading.

- If vacuum does not drop, install the fuel sender and fuel tank.
- If vacuum drops, replace the fuel sender, install the fuel tank, connect the fuel pipe and go to Step 5.

5. Start and run the engine, observing the fuel for air bubbles:

- If air bubbles are present, stop the engine and recheck Steps 3 and 4.
- If air bubbles are not present, stop the engine and go to Step 6.

6. Remove the transparent hose and connect the hose of the filter outlet to the injection pump inlet fitting.
7. Disconnect the return hose at the injection pump.
8. Install a transparent hose between the injection pump and the hose of the return line.
9. Start and run the engine. observing the fuel for air bubbles:

NOTE: It is ok to see a small stream of bubbles on snap acceleration.

- If air bubbles are not present, go to Step 10.
- If air bubbles are present, replace the injection pump.

10. Stop the engine.
11. Remove the transparent hose and attach the fuel return hose at the injection pump.
12. Clean any fuel spillage.
13. Run the engine to check for fuel leakage.

LIFT PUMP ELECTRICAL CIRCUIT
For diagnosis of the lift pump electrical circuit, refer to CHART A-5. Testing and Inspection