Note. The work on checking the working pressure in the fuel rail is shown on the VAZ 21124 engine (1.6i). Checking the fuel pressure on the VAZ 2112 engine (1.5i) is performed similarly. In this case, it is difficult to connect the pressure gauge - you have to bend the hose strongly, since it rests against the rear timing belt cover.
Warning: Before performing a fuel pressure test in the fuel rail, read the safety rules for servicing and repairing the fuel system (see "Safety precautions for maintenance and repair of the power supply system").
To perform repair work to check the fuel pressure in the fuel rail, you will need a special pressure gauge (see item 26 "Special tools and devices").
Sequence of execution of the check
1. Preparing the vehicle for work (see point 2a "Preparing a car for maintenance and repair").
2. Remove the decorative engine cover (see "Engine trim - removal and installation")
3. Unscrew the protective cap of the diagnostic connector of the fuel rail.
4. Connect the pressure gauge hose tip to the fuel rail fitting.
5. Using a 14 mm open-end wrench, tighten the hose tip.
Recommendation. 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 release the fuel pressure (see "Fuel line - pressure relief"). After this, unscrew the valve from the fuel rail fitting. This can be done with a metal cap of the wheel valve. To connect the pressure gauge to the fuel rail fitting, use a piece of gasoline-resistant hose of a suitable diameter. The ends of the hoses must be securely fastened with clamps.
6. Turn on the ignition on the car. The fuel pump will work for a few seconds. Wait until the pump stops working, then turn off the ignition.
7. To remove air from the pressure gauge, lower the end of the drain tube into a small container, unscrew the pressure gauge bleed nipple by 1/3-1/2 turn, and release excess gasoline pressure from the fuel rail. This will remove air from the pressure gauge hose.
8. Tighten the bleed nipple until it stops.
We start the engine of the car and measure the operating pressure in the fuel rail at different crankshaft speeds. For a serviceable engine, it should be within the range: for the VAZ 2112 engine - 284-325 kPa (2.8-3.2 bar); for VAZ 2112 engine - 378-390 kPa (3.8-3.9 bar).
9. Turn off the ignition.
10. After lowering the end of the tube into the container, open the fitting and release the pressure from the fuel line.
11. Disconnect the pressure gauge from the diagnostic fitting of the fuel rail.
12. Screw the protective cap onto the fuel rail fitting.
Recommendation: If the operating pressure in the fuel rail is not stable or is higher than normal, then the fuel pressure regulator is faulty (see "Fuel module engine 21124 (1.6i) - replacement of fuel pressure regulator" for engine 21124 or see. "Fuel rail engine 2112 (1.5i) - removal, disassembly, assembly and installation", for engine 2112). Low pressure in the fuel rail (below normal) can also be caused by a faulty fuel pressure regulator. The fuel pump mesh filter may be clogged or the fuel pump may not be producing the required pressure. To clean the fuel pump mesh filter, you will need to remove the fuel module (see "Fuel module engine fuel pump 21124 (1.6i) - cleaning the mesh filter" for engine 21124 or see. "Fuel module of the gasoline pump of the engine 2112 (1.5i) - cleaning the mesh filter" for engine 2112).