Sequence of execution
1. Prepare the car for work (see "Preparing the car for maintenance and repair").
2. Unscrew the protective cap of the diagnostic connector of the fuel rail.
3. Connect the tip of the pressure gauge hose to the diagnostic fitting of the fuel rail. We tighten the end of the hose using an open-end wrench.
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If necessary, the pressure in the fuel rail can be measured with a homemade device made from a pressure gauge from a foot pump. Before connecting such a pressure gauge, it is necessary to relieve the fuel pressure. After this, unscrew the valve from the fuel rail fitting. This can be done with a metal wheel valve cap. To connect the pressure gauge to the fuel rail fitting, use a piece of fuel-resistant hose of a suitable diameter. The ends of the hoses must be securely fastened with clamps.
4. Turn on the ignition. The fuel pump will operate for a few seconds. After waiting for the pump to stop working, turn off the ignition.
5. To remove air from the pressure gauge, lower the end of the drain tube into a small container, unscrew the pressure gauge bleeder nipple by ⅓-½ turn and release excess gasoline pressure from the fuel rail. This will remove air from the pressure gauge hose.
6. Tighten the bleed nipple until it stops.
We start the engine and measure the operating pressure in the fuel rail at different crankshaft rotation speeds. For a serviceable engine it should be within 378-390 kPa (3.8-3.9 bar).
7. Turn off the ignition.
8. After lowering the end of the tube into the container, open the fitting and release the pressure from the fuel line.
9. Disconnect the pressure gauge from the diagnostic fitting of the fuel rail.
10. Screw the protective cap onto the fuel rail fitting.
Recommendation. If the operating pressure in the fuel rail is unstable or higher than normal, then the fuel pressure regulator is faulty. Low pressure (below normal) it can also be caused by a faulty regulator. The fuel pump mesh filter may be clogged, or the fuel pump may not be producing the required pressure. To clean the mesh filter you need to remove the fuel module. You can verify that the pressure regulator and fuel pump are faulty by replacing them with known good ones. It is also possible to replace the fuel module assembly.