B12 - B17 Checking Fuel Pumps, Fuel Pressure and Regulator
B12 Connect Pressure Gauge 5011Fuel Pumps, Line And Pressure Regulator:
- Connect gauge between fuel pipe and fuel distribution manifold, use hose 5116 and nipple 5265,
- Plug open end of hose with 5266.
- Turn gauge cock to position 1, pointing toward hose 5116.
B13 Check Function Of Fuel Pump And Tank Pump
- Remove panel above foot pedals.
- Disconnect pressure sensor.
- Turn on ignition.
- Connect wire (in connector) from relay to ground. (Note: both wires are yellow/black, check which one is ground).
- Fuel pumps should start and be clearly heard.
B14 Check Tank Pump
- Unscrew fuel filler cap and listen.
- It is also possible to connect an ammeter between the fuse and pump wiring.
- 740 1985-on: fuse 11
- 760 up to 1987: fuse 11
- 760 1988/89: fuse 11/30
- Current consumption: 1-2 A.
If neither pump operates:
- Turn off ignition.
- Pull out central electrical unit and remove [1][2]system relay.
- check for voltage at terminal 30
- No voltage:
- Check wiring between relay and battery.
- Connect a wire between terminals 30 and 87/2 in relay socket.
- Both pumps should start.
- If pumps start:
- Carry out Fault Tracing steps B10-B18 and check why relay doesn't function, refer to Fault Tracing steps C1-4, and C8-1O.
- If pumps do not start:
- Check wiring between relay and pumps.
- Connect a wire between terminals 87/1 and 85 to check for a break.
- Use an ohmmeter or test buzzer.
B15 Measure line pressure
Measuring System Pressure:
- Line pressure = 300 kPa (42 psi).
If line pressure is too high:
- Disconnect wire in pump relay socket from terminals 30 and 87/2.
- Disconnect return fuel line from pressure regulator. Blow through fuel line.
- Disconnect vacuum hose from pressure regulator. Blow through hose.
- If there are no blockages the pressure regulator is probably defective. Install new regulator and measure line pressure.
If line pressure is too low:
- Pinch fuel return line with hand and check pressure increase.
IMPORTANT Do not allow pressure to exceed 600 kPa (85 psi).
If pressure rises quickly, pumps and fuel lines are OK.
- Install new regulator and remeasure pressure.
If pressure rises slowly, this indicates a blocked fuel filter, tank plump filter or fuel line.
- Check/Replace fuel filter, tank pump filter or fuel line.
If pressure does not rise the fuel pump is probably defective.
B16 Check Pressure Regulator
- Connect a vacuum pump to pressure regulator.
- Pump air out of pressure regulator and check that drop in line pressure is same as drop in regulator pressure.
300 kPa (42 psi) - vacuum = line pressure
Installing Pressure Pump And Gauge:
- Connect pressure tester and pump/gauge 5230 to pressure regulator.
- Increase pressure and check line pressure increase.
IMPORTANT Do not exceed 70 kPa (10 psi).
- Line pressure should increase to same extent as increase in regulator pressure.
300 kPa (42 psi) + pressure = line pressure
- Replace defective pressure regulator.
- Reconnect hose between pressure regulator and intake manifold.
B17 Turn Off Fuel Pumps
- Disconnect ground wire from pressure sensor and reconnect connector.
- Disconnect wire from terminals 30 and 87/2 in relay socket.
- Install relay.
Remove pressure gauge
- Hold absorbent paper below fuel line to absorb spillage when disconnecting gauge.
IMPORTANT! If plastic fuel line ties have been removed they must be reinstalled.