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4-3-proverka-davleniya-topliva-toplivnogo-nasosa.html
4.3. Check of pressure of fuel / fuel pump
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Fuel is extremely inflammable, therefore, working with any part of fuel system, accept additional precautionary measures. Do not smoke, and do not allow emergence near a working zone of open fire or a lamp without a plafond. Also do not work in garage with the equipment at natural gas with burning match. |
Carburetor engines
For check of the fuel pump it is necessary between an exit of the fuel pump and a tube of supply of fuel in the carburetor to connect a suitable measuring instrument of pressure.
For this dough it is necessary зашунтировать the return valve of fuel which is normally included in the fuel line from the fuel pump to the carburetor.
At operation of the engine idling pressure of the pump should make size between 0.1 and 0.3 atm.
If the measuring instrument of pressure is inaccessible, to check the fuel pump it is possible the next simpler way (but also less exact). Disconnect a target hose of the fuel pump.
Disconnect from the ignition coil a high-voltage wire not to allow fuel flash in the engine, then turn the engine a starter. Fuel should follow from a target hose distinct pushes.
Engines with fuel injection
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On late models the electric fuel pump is located in a fuel tank, and on early models - near a tank. Early models are also equipped with the intermediate pump located in a fuel tank. The intermediate pump feeds the main pump, but is not capable to create the high pressure demanded by system. |
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The fuel pump in Motronic systems turns on low level of a signal from the Motronic (ECU) control unit. The fuel pump after inclusion of ignition works some seconds, and then continues functioning, only when the engine starts to work. |
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In the following checks it is supposed that the fuel filter is in a good condition. If there are doubts in quality of the fuel filter, replace it (look Head Routine maintenance of the car). |
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For receiving exact results of dough 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
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- 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)...
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... or 30 and 87 (Motronic systems).
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- On all models, since 1989, for ensuring access to the relay of the fuel pump and ECU, unscrew four bolts and remove a protective cover...
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... then a crossing point connect in the socket contacts 30 and 87 which relays of the fuel pump correspond
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- Let the assistant will include ignition while you will listen to sounds in a fuel tank. Some seconds should be audible hum.
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This check also belongs to the intermediate pump. If it is not audible hums, a problem in a chain of the fuel pump. First of all check the main relay and a safety lock of the fuel pump (look Head System of onboard electric equipment). If the main relay as it should be, check the relay of the fuel pump. |
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Pressure check in fuel system
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- Remove in fuel system pressure (look the Section pressure Removal in system of injection of fuel).
- Disconnect a negative wire of the storage battery.
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- Disconnect from the fuel highway of L-Jetronic system or early model of Motronic system the line of supply of fuel or on late systems Motronic disconnect the main fuel line from the fuel filter.
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- Without breaking a normal stream of fuel, by means of a tee, a short piece of a fuel hose of a high pressure and collars attach a measuring instrument of pressure of fuel.
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For this check do not use a tee from plastic. It will not sustain pressure in fuel system. |
- Connect the battery.
- Short-circuit a piece of a wire of the plug of the relay of the fuel pump.
- Include ignition.
- Write down size of pressure and compare it to the given value in the Size table and adjusting data at the end of the Management.
- If pressure in fuel system is lower than the demanded:
- Check existence in system of leaks. Eliminate all leaks and repeat pressure check
- If leaks are absent, establish the new fuel filter and again check pressure of fuel.
- If pressure all the same low, check pressure of the fuel pump (look below) and a regulator of pressure of fuel (look the Section Check of functioning and replacement of a regulator of pressure of fuel).
- If pressure is higher demanded, check lack of a contamination of the line of return of fuel. If the line as it should be, replace a regulator of pressure of fuel.
- Switch off ignition, wait for five minutes and check the indication of a measuring instrument of pressure. Compare the indication to value of residual pressure in the system, given in the Size table and adjusting data at the end of the Management. If residual pressure is lower than the demanded:
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Check of functioning of the fuel pump
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For this check the pressure measuring instrument with the pitting valve is required. After completion of check normal procedure of removal of pressure will be unacceptable, as the measuring instrument is connected directly to the fuel pump. |
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- Remove in fuel system pressure (look the Section pressure Removal in system of injection of fuel).
- Attach a negative wire of the storage battery.
- Disconnect from the fuel highway a hose of supply of fuel and directly to a hose connect a pressure measuring instrument.
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If the tee is still attached to a measuring instrument, muffle the open end. |
- Connect the storage battery.
- Piece of a wire short-circuit contacts of the relay of the fuel pump.
- Include ignition that the fuel pump earned.
- Write down the indication of a 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.
- If the measured pressure less demanded, examine the fuel line between the pump and a measuring instrument about leaks. If leaks it is not revealed, replace the fuel pump.
- Switch off ignition and wait for five minutes. Write down the indication of a measuring instrument and compare to 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 less demanded, check existence of leaks in the fuel line between the pump and a measuring instrument. If leaks are not found, replace the fuel pump.
- Disconnect a crossing point. Remove pressure, having opened on a measuring instrument pitting valve and having merged fuel in the suitable container. Disconnect a measuring instrument and attach the fuel line.
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Check of pressure of the intermediate pump
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- Remove in fuel system pressure (look the Section pressure Removal in system of injection of fuel).
- Disconnect a negative wire of the storage battery.
- 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 a luggage compartment). Disconnect from the intermediate pump a target hose and to a target tube connect a measuring instrument of pressure of fuel.
- Connect the storage battery.
- Crossing point short-circuit contacts of the relay of the fuel pump.
- For turning on of the fuel pump include ignition.
- Write down the indication of a measuring instrument and compare to the value given in the Size table and adjusting data at the end of the Management.
- If the measured pressure less demanded, replace the intermediate pump.
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Check of the relay of the fuel pump
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- Include ignition.
- By means of the voltmeter from a reverse side of the socket of the relay check tension on contacts. Check existence of tension of the storage battery on contact 30 (engines M20 and М30) or contact 15 (engines M10 and М40).
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If on models with the storage battery located in a luggage compartment tension is absent, check a safety wire. The safety wire of 50 amperes is located in a black cover in 15 cm from the battery. |
- 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 engines M20 and М30 or between contact 50 and the case on engines M10 and М40. When the assistant will include ignition, take readings of the voltmeter. The voltmeter should show tension of the battery.
- 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, replace the relay.
- 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, the intermediate pump and the fuel level sensor). If necessary replace the fuel pump.
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