13 31... Notes on fuel pressure check (reference pressure: environment): Notes
Feature of this version with ambient pressure:
The connection for the vacuum hose of the fuel pressure regulator is located between the throttle and the air cleaner or on the air cleaner.
Test precondition:
The correct fuel pressure regulator is fitted.
- Using the EPC, check whether the fuel pressure regulator suitable for the car is fitted:
Connect test adapter.
Description of operation:
The control function of the fuel pressure regulator must be guaranteed under all operating conditions. The fuel pump must always be able to generate a higher fuel pressure than the pressure regulated by the pressure regulator.
The injection rate is adjusted by means of the injection time; the injection time is controlled by the DME.
Description of operation: fuel return line
When the engine is at a standstill and the ignition key is in position 0, the fuel return line after the pressure regulator is at zero pressure.
Description of operation: pressure retaining function
The pressure regulator closes when the engine is at a standstill and the ignition key is in position 0. The fuel pressure in the delivery line is retained over an extended period. A non-return valve closes in the fuel pump. These measures help to retain the fuel pressure in the fuel system. Extended starting times are thus avoided.
Complaint: drive characteristic faults, lack of power
- Run engine at idle speed and measure fuel pressure.
If the measured value is less than the nominal value - 0.2 bar:
- Line cross-sections in fuel feed are constricted or fuel filter is clogged,
or
- Fuel pump voltage supply is not OK.: e.g. as a result of high contact resistance (corrosion) in plug connection between wiring harness and fuel pump.
If the measured value is greater than the nominal value + 0.2 bar:
- Turn off engine stop and then observe measured value.
- If measured value drops to nominal value, then line cross-sections in fuel return are constricted or clogged.
- Check the fuel lines for kinks.
If no kinks are visible:
- Replace return lines
If measured value remains too high, then pressure regulator is in all probability faulty.
- Have a cleaning cloth ready and catch and dispose of escaping fuel.
- Replace the return line but not the pressure regulator.
Complaint: starting problems
- Run engine briefly at idle speed and switch off.
- Note down measured value while engine is stopped.
- Read off measured value again after approx. 20 to 30 minutes while engine is stopped.
Special tool 13 3 010 (hose clamp) is required for the following test.
If the measured value has dropped by more than 0.5 bar:
- Start engine and wait briefly for a stable pressure increase.
- Switch off the engine and immediately pinch off the delivery line just before the pressure gauge with the special tool 13 3 010.
- Note down measured value
- Read off measured value again after approx. 20 to 30 minutes while engine is stopped