Checking Residual Pressure

Checking Residual Pressure




1 Connect as described in "Connection of pressure testing equipment". Connection of Pressure Testing Equipment

2 Start the fuel pump by setting the switch to the ON position. Read off the system pressure.




3 Stop the fuel pump by setting the switch to OFF. The pressure should now immediately drop 0.1
- 0.2 bar (1.4 - 2.8 psi).




4 If the residual pressure has dropped more than 0.7 bar after about 20 minutes, check the fuel pressure regulator and the fuel pump's non- return valve for leakage.

Quick check
- Check the fuel lines for external leakage.
- Start the pump and run up the pressure. Then turn off the pump again.
- Remove the return line from the fuel pressure regulator. If fuel runs out of the regulator, it is faulty. Change the fuel pressure regulator.
- If the regulator is OK and the pressure drops rapidly, there is probably a leak in the non-return valve. Try fitting a replacement and check again.
- If the pressure drops slowly, the fault is probably in an injector. Remove and check.

Useful tip
On cars with a long return hose of rubber which can be pinched off without damage, it might be possible to flush out any foreign objects lodged in the fuel pressure regulator's non-return valve.
- Start the pump.
- Pinch the hose briefly, max. 1 second.
- Repeat several times.