Testing Fuel Pump Delivery Rate

To Test Fuel Pump Delivery Rate:
1. Before testing the main fuel pump, check that the transfer pump is working correctly.
2. Disconnect the fuel return line as shown in Fig. 4-7 or Fig. 4-8 and route the end of the fuel return line to a measurement container of at least 1000 ml (1 qt.).

Fig. 4-7:

Fig. 4-7. Container being used to measure fuel delivery rate at fuel return line (CIS or CIS-E and CIS-E Motronic). Return line connection (arrow) is located near right (passenger side) front suspension strut tower.

WARNING: Fuel will be expelled under pressure as the line is disconnected. Do not disconnect wires that could cause sparks. Do not smoke or work near heaters or other fire hazards. Keep a fire extinguisher handy.

3. Run the fuel pump, for exactly 30 seconds.
4. On models with Digifant, the pump should deliver at least 500 cc (17 oz.) of fuel.

Fig. 4-8:

Fig. 4-8. Container being used to measure fuel delivery rate at return line (Digifant). Return line from fuel pressure regulator (lower right) is disconnected (arrow) near right (passenger side) front suspension strut tower.

5. On models with CIS, CIS-E or CIS-E Motronic, the correct amount of fuel delivered depends on voltage at the pump while the pump is running. See the chart in Fig. 4-9 for exact specifications.

Fig. 4-9:

Fig. 4-9. Minimum amount of fuel to be delivered by fuel pump in 30 seconds of operation. Chart shows fuel delivery vs. voltage at fuel pump with pump running (approximately 2 volts less than battery voltage).

It the fuel pump does not run, test as described below under Fuel Pump Electrical Tests. If fuel delivery is below specifications, check for leaks, blocked or kinked lines, a blocked filter, or a blocked transfer pump strainer/filter. If no such causes for low fuel delivery are found, the fuel pump is probably faulty and should be replaced.