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4.3. Check of pressure of fuel / fuel pump

Fuel is extremely flammable therefore, working with any part of fuel system, take additional precautionary measures. You do not smoke, and do not allow emergence near a working zone of naked flame or a lamp without plafond. Also do not work in a garage with the equipment on natural gas with the burning match.

Carburetor engines

It is necessary for check of the fuel pump between an exit of the fuel pump and a tube of supply of fuel in the carburetor to connect the suitable measuring instrument of pressure.

For this test it is necessary to zashuntirovat the backpressure valve of fuel which is switched normally on in the fuel line from the fuel pump to the carburetor.

During the operation of the engine idling pressure of the pump has to make size between 0.1 and 0.3 atm.

If the measuring instrument of pressure is inaccessible, then it is possible to check the fuel pump the following easier way (but also less exact). Disconnect an output hose of the fuel pump.

Disconnect a high-voltage wire from the ignition coil not to allow flash of fuel in the engine, then turn the engine a starter. Fuel has to follow from an output hose distinct pushes.

Engines with fuel injection

On late models the electric fuel pump is located in the fuel tank, and on early models - near a tank. Early models are also equipped with the intermediate pump located in the fuel tank. The intermediate pump feeds the main pump, but is not capable to create the high pressure demanded by system.


The fuel pump in the Motronic systems turns on the low level of a signal from the Motronic (ECU) control unit. The fuel pump after inclusion of ignition works several seconds, and then continues functioning, only when the engine begins to work.


In the following checks it is supposed that the fuel filter is in good shape. If there are doubts in quality of the fuel filter, replace it (watch Chapter Routine maintenance of the car).


For obtaining exact test results it is recommended to measure pressure and the main fuel pump and intermediate if it is applied.

Check of functioning of the fuel pump / intermediate pump

 PERFORMANCE ORDER

  1. Connect among themselves a suitable wire contacts of the socket relating to the relay of the fuel pump, namely, 30 and 87b (L-Jetronic systems)...

... or 30 and 87 (Motronic systems).

  1. On all models, since 1989, for ensuring access to the relay of the fuel pump and ECU, turn off four bolts and remove a protective cover...

... then a crossing point connect contacts 30 and 87 which correspond to the relay of the fuel pump in the socket

  1. Let the assistant will include ignition while you will listen to sounds in the fuel tank. Several seconds have to be heard hum.

This check also belongs to the intermediate pump. If it is not heard hums, then a problem in a chain of the fuel pump. First of all check the main relay and a safety lock of the fuel pump (watch the Head Sistem of onboard electric equipment). If the main relay as it should be, then check the relay of the fuel pump.

Check of pressure in fuel system

 PERFORMANCE ORDER

  1. Take off pressure in fuel system (watch the Section Removal of Pressure in system of injection of fuel).
  2. Disconnect a negative wire of the rechargeable battery.

If the radio receiver of your car is equipped with system of protection against stealing, before shutdown of the battery be convinced that the correct code of activization is known. Before a detachment of a wire apply for information to the Section System of Protection of the Audio System from theft and language of an instrument guard of this management.


If after shutdown of the battery on the display of the dashboard the message in other language appears, for the procedure of installation of language address the Section System of Protection of the Audio System from theft and language of an instrument guard.


  1. Disconnect the line of supply of fuel from the fuel highway of the L-Jetronic system or early model of the Motronic system or on the late Motronic systems disconnect the main fuel line from the fuel filter.
  1. Without breaking a normal stream of fuel, by means of a tee, a short piece of a fuel hose of high pressure and collars attach the fuel pressure measuring instrument.

For this check do not use a tee from plastic. It will not sustain pressure in fuel system.

  1. Connect the battery.
  2. Short-circuit a piece of a wire of the plug of the relay of the fuel pump.
  3. Include ignition.
  4. Write down the size of pressure and compare it to the given value in the Size table and adjusting data at the end of the Management.
  5. If pressure in fuel system is lower than demanded:
  6. If pressure is higher than demanded, check lack of a contamination of the line of return of fuel. If the line as it should be, replace the fuel pressure regulator.
  7. Switch off ignition, wait five minutes and check the indication of the measuring instrument of pressure. Compare the indication to the value of residual pressure in system given in the Size table and adjusting data at the end of the Management. If residual pressure is lower than demanded:

Check of functioning of the fuel pump

This check will require pressure measuring instrument with the pitting valve. After completion of check the normal procedure of removal of pressure will be unacceptable as the measuring instrument is connected directly to the fuel pump.


 PERFORMANCE ORDER

  1. Take off pressure in fuel system (watch the Section Removal of Pressure in system of injection of fuel).
  2. Attach a negative wire of the rechargeable battery.

If the radio receiver in your car is equipped with system of protection against stealing, before shutdown of the battery be convinced that the correct code of activization is known. Before a detachment of a wire apply for information in the Section System of Protection of the Audio System from theft and language of an instrument guard of this management.


If after connection of the battery on the display of the dashboard the message in other language appears, then for the procedure of installation of language address the Section System of Protection of the Audio System from theft and language of an instrument guard.

  1. Disconnect a hose of supply of fuel from the fuel highway and directly connect pressure measuring instrument to a hose.

If the tee is still attached to the measuring instrument, then muffle the open end.

  1. Connect the rechargeable battery.
  2. Piece of a wire short-circuit contacts of the relay of the fuel pump.
  3. Include ignition that the fuel pump started working.
  4. Write down the indication of the measuring instrument of pressure and compare pressure size to the value given in the Size table and adjusting data at the end of the Management.
  5. If the measured pressure is less than demanded, examine the fuel line between the pump and the measuring instrument regarding leaks. If leaks are not revealed, replace the fuel pump.
  6. Switch off ignition and wait five minutes. Write down the indication of the measuring instrument and compare to the value of residual pressure of the fuel pump given in the Size table and adjusting data at the end of the Management. If residual pressure is less than demanded, check existence of leaks in the fuel line between the pump and the measuring instrument. If leaks are not found, replace the fuel pump.
  7. Disconnect a crossing point. Take off pressure, having opened the pitting valve on the measuring instrument and having merged fuel in a suitable container. Disconnect the measuring instrument and attach the fuel line.

Check of pressure of the intermediate pump

 PERFORMANCE ORDER

  1. Take off pressure in fuel system (watch the Section Removal of Pressure in system of injection of fuel).
  2. Disconnect a negative wire of the rechargeable battery.

If the radio receiver in your car is protected from stealing, before shutdown of the battery be convinced that the correct code of activization is known. Before a detachment of a wire apply for information in the Section System of Protection of the Audio System from theft and language of an instrument guard.


If after connection of the battery on the display of the dashboard the message in other language appears, then for the procedure of installation of language address the Section System of Protection of the Audio System from theft and language of an instrument guard.

  1. Remove the hatch of access to the intermediate pump (on some models it is located under a back seat, on others - under a rug of the luggage compartment). Disconnect an output hose from the intermediate pump and connect the fuel pressure measuring instrument to an output tube.
  2. Connect the rechargeable battery.
  3. Crossing point short-circuit contacts of the relay of the fuel pump.
  4. For turning on of the fuel pump include ignition.
  5. Write down the indication of the measuring instrument and compare to the value given in the Size table and adjusting data at the end of the Management.
  6. If the measured pressure is less than demanded, replace the intermediate pump.

Check of the relay of the fuel pump

 PERFORMANCE ORDER

  1. Include ignition.
  2. By means of the voltmeter from a reverse side of the socket of the relay check tension on contacts. Check presence of tension of the rechargeable battery on contact 30 (M20 and M30 engines) or contact 15 (M10 and M40 engines).

If on models with the rechargeable battery located in the luggage compartment tension is absent, then check a safety wire. The safety wire of 50 amperes is located in a black cover in 15 cm from the battery.

  1. Switch off ignition and disconnect from the relay socket. By means of the voltmeter check tension on the corresponding relays of the fuel pump contacts 85 (-) and 86 () for M20 and M30 engines or between contact 50 and the case on M10 and M40 engines. When the assistant includes ignition, take readings of the voltmeter. The voltmeter has to show battery tension.
  2. If tension is absent, check a safety lock (safety locks) and wires of the relay of the fuel pump. If indications correct and the fuel pump works only with a crossing point, then replace the relay.
  3. If the fuel pump nevertheless does not work, check tension on contacts of the fuel pump (look the Section Removal and installation of the fuel pump, intermediate pump and fuel level sensor). If necessary replace the fuel pump.