Generic Scan Tool MFI
Fuel Pump, Checking
Special tools, testers and auxiliary items required
• Wrench
• Pressure gauge
• Torque wrench
• Hand held remote starter (jumper)
• Low current voltage tester
• Measuring container
Checking function and voltage supply => [ Function and Voltage Supply, Checking ].
Checking fuel delivery => [ Delivery Rate, Checking ].
Checking current draw => [ Current Draw, Checking ].
Fuel Pump (FP) check-valve, checking => [ Fuel Pump Check-Valve, Checking ].
Function and Voltage Supply, Checking
• Battery voltage at 12.5 V
• Fuse for Fuel Pump (FP) on fuse holder OK.
- Switch ignition on.
• Fuel Pump (FP) must briefly start up audibly.
• Fuel Pump (FP) runs quietly.
- Switch off ignition.
If Fuel Pump (FP) does not start up
- Remove seat bench.
- Remove cover - 1 - from fuel delivery unit in direction of arrow - 2 -.
• On vehicles with auxiliary heater, harness connector of Metering Pump (V54) must also be disconnected.
- Disconnect the electrical harness connector - 1 -.
- Connect Low current voltage tester to outer terminals of connector.
- Switch ignition on.
• LED must light up briefly.
If LED does not light up briefly:
- Locate and repair open circuit in wiring.
LED lights up briefly (voltage supply OK)
- Remove fuel delivery unit.
- Check if electrical wiring between flange and fuel pump is connected.
If no open circuits are found:
- Fuel Pump (FP) faulty, replace fuel delivery unit.
Delivery Rate, Checking
• Voltage supply OK.
• Fuel pressure regulator and residual pressure OK
• Fuel filter OK.
- Remove fuel filler cap from fuel filler tube.
- Remove seat bench.
- Remove cover - 1 - from fuel delivery unit. Arrow - 2 - points in direction of travel.
- Disconnect harness connector - 1 - from fuel delivery unit.
- Connect Hand held remote starter (jumper) to terminal - 1 - of Fuel Pump (FP) and to battery plus (+).
- Connect terminals - 5 - of harness connector and Fuel Pump (FP)
• Delivery rate of Fuel Pump (FP) is measured at 4 bar. Therefore, measure fuel pressure before measuring delivery rate.
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the fuel lines, place a rag around the connection point. Then release pressure by carefully pulling hose off connection.
- Disconnect return line - 1 - from fuel pressure regulator.
• Press in securing ring to disengage the fuel line.
- Connect hose to fuel pressure regulator and hold end of the hose into a measuring container.
- Operate Hand held remote starter (jumper) approx. 5 seconds in order to fill fuel filter.
- Empty measuring container.
- Delivery rate of Fuel Pump (FP) is dependent on voltage. Therefore connect multimeter to battery.
- Operate remote control for 30 seconds and measure battery voltage.
- Compare quantity of fuel delivered with specification.
Minimum delivery rate cm3/30 s
Voltage at fuel pump with engine off and pump running (approx. 2 Volts less than battery voltage).
Example:
During test, a voltage of 12.5 volts is measured at battery. Since voltage at pump is approx. 2 Volts less than battery voltage, there is a minimum delivery rate of 580 cm3/30 s.
If minimum delivery rate is not attained:
- Check supply line to filter for possible restrictions (kinks) or clogging.
If fuel line is OK:
- Check fuel delivery rate in front of fuel filter.
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the fuel lines, place a rag around the connection point. Then release pressure by carefully pulling hose off connection.
- Disconnect supply line - 1 - from fuel filter input.
• Press in securing ring to disengage the fuel line.
- Connect pressure gauge as shown.
- Connect siphon hose to pressure gauge and hold it in a measuring container.
CAUTION!
Danger of spraying when opening shut-off valve! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold container in front of free connection of pressure measuring device.
- Open shut-off valve of pressure gauge. Lever will point in direction of flow - A -.
- Operate Hand held remote starter (jumper). Slowly close shut-off tap, until pressure gauge shows 4 bars. From this point on do not move position of shut-off tap.
- Empty measuring container.
- Operate Hand held remote starter (jumper) again for 30 seconds. Compare delivery rate with value determined from first measurement.
If minimum delivery rate is now obtained:
- Replace fuel filter.
If minimum delivery rate is again not obtained:
- Remove fuel delivery unit and check filter strainer for dirt.
Only, when up to now, no malfunction has been detected:
- Replace fuel delivery unit.
- Reconnect all disconnected fuel lines.
- Bleed fuel supply system.
Delivery rate has been obtained, but malfunctions are still suspected in fuel supply, for example sporadic loss of fuel supply:
- Check Fuel Pump (FP) current draw => [ Current Draw, Checking ].
Current Draw, Checking
- Remove seat bench.
- Remove cover - 1 - from fuel delivery unit. Arrow - 2 - points in direction of travel.
- Connect current probe - A - around cable - B - of 5-pin harness connector.
- Start engine and run at idle speed.
- Measure current draw of fuel pump.
Specification: max. 9 amps.
• If malfunction in fuel system is sporadic, test can also be performed during a road test, but a second person is required.
If current draw is exceeded:
- Fuel Pump (FP) faulty, replace fuel delivery unit.
Fuel Pump Check-Valve, Checking
- Remove seat bench.
- Remove cover - 1 - from fuel delivery unit. Arrow - 2 - points in direction of travel.
- Disconnect the electrical harness connector from fuel delivery unit.
- Connect a hand held remote starter (jumper) to terminal - 1 - of Fuel Pump (FP) and to battery plus (+).
- Connect terminals - 5 - of harness connector and Fuel Pump (FP) using a jumper wire.
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the fuel lines, place a rag around the connection point. Then release pressure by carefully pulling hose off connection.
- Disconnect supply line - 1 - from fuel filter input.
• Press in securing ring to disengage the fuel line.
- Connect pressure gauge as shown.
- Connect siphon hose to pressure gauge and hold it in a measuring container.
- Close shut-off valve of pressure gauge (lever perpendicular to direction of flow, position - B -).
- Operate remote control at short intervals, until a pressure of approx. 4 bars has built up.
CAUTION!
Danger of spraying when opening shut-off valve; wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold container in front of free connection of pressure measuring device.
- If pressure builds up too high, lower excess pressure by carefully opening shut-off tap.
- Watch pressure drop on gauge.
After 10 minutes pressure must not drop below a 3 bar decrease.
If pressure drops further:
- Check line connections for leaks.
If no fault is detected in wiring:
- Fuel Pump (FP) faulty, replace fuel delivery unit.