Fuel Pressure Diagnostics
If the gasoline engine, when idling, “dulls” or “tones”, the tachometer needle jumps, then it is immediately difficult to determine what the problem is. The most likely causes: a malfunction in the fuel equipment or severe wear of the engine’s CPG (compression drop). These two parameters are usually diagnosed one after another. In this case, we will deal with checking the pressure in the vehicle.
Any fuel system of a car is a vicious circle. Gasoline under pressure pumped by the pump flows from the tank through the fuel filter into the fuel rail: to the injectors and the fuel pressure regulator, and unused fuel is returned to the tank. On each of the elements associated with the passage of gasoline through it, a pressure change in one direction or another is possible.
The amount of gasoline injected depends on the injector operating time, on the pressure inside the fuel rail and on the pressure (vacuum) inside the intake manifold. In order to take into account these three factors and more accurately calculate the amount of fuel injected, a fuel pressure regulator is installed in the fuel rail. It maintains the pressure difference: gas pressure at the nozzle and air pressure in the intake manifold, excess gas is sent back to the tank through the return line.
Due to wear or malfunction, the regulator may decrease or increase the pressure in the fuel rail. As a result, we have: a lack or overflow of fuel and loss of power in the engine. Valve jamming can also occur, in this case the pressure in the fuel rail will not change regularly, as a result of which there may be unstable engine operation, jerking during acceleration.
Fuel rail pressure diagnostics is an important parameter in troubleshooting engine fuel equipment. After all, the composition of the fuel mixture depends on it, respectively, and the behavior of the car in various operating modes. Therefore, the diagnosis of the gasoline engine injection system is an important component in the overall diagnosis of the engine.
Types of fuel pressure gauges
For the simplest diagnosis, a fuel pressure gauge is required. The scale at the pressure gauge should be at least 7 bar. The best option for price and quality is suitable for personal use or a small car service device HS-1013 (TU-113). It allows you to assess the condition of the following systems: pump pressure, pump performance, leaks, clogged fuel filter, check the efficiency of the pressure regulator. The set of adapters included in the kit allows you to measure the pressure in the fuel system on all cars of domestic and many imported cars. Diagnosis is quite simple for them, you can do it yourself.
In car services, more professional sets are used to measure fuel pressure: TU-114 (HS-0020), ATZ-602 or TU-443 (HS-1011) and ATZ-600 fuel pressure gauge, a set of adapters in which allows you to connect to various points to the car power system on most car brands.
Before starting the diagnosis, it is necessary to carefully inspect the entire fuel line, make sure of its integrity, the absence of smudges, and corrosion. It is also necessary to check the operability of the electrical elements of the fuel equipment.
When the engine is running, the pressure in the fuel rail must correspond to the passport data for the corresponding brand of car. For example: the normal fuel pressure for VAZ, GAZ, UAZ is 2.8-3.2 bar. The reason for low pressure is usually associated with problems in the supply line, and the reason for high pressure is associated with problems in the return.
An injector is a simple solenoid valve designed to accurately meter gasoline and spray it in a combustion chamber. During the operation of the car, components resembling bitumen and varnishes are released from the fuel. The lower the quality of the fuel, the more these impurities. They accumulate on the metering elements of the injectors and in the fuel rail.
To the fuel deposits here are added deposits from engine oil entering the engine intake system through the crankcase ventilation system, especially in a worn out engine. Due to these deposits, the flow cross sections are reduced and the regulation of the fuel-air mixture decreases towards its depletion.
To take the injector out of its normal working condition, not much is needed. Driving on low-quality fuel, driving in the city cycle and short distances with an engine that is not warm enough leads to the fact that deposits in the injectors form faster than they dissolve with detergents contained in gasoline. A decrease in the throughput of one injector by 8-10% is quite enough to start the misfire. If this happens, unburned oxygen enters the exhaust system and destroys the oxygen sensor.
Another component that you must pay attention to is the throttle. Fuel vapors rising from the intake manifold usually settle on the throttle and parts adjacent to it. The result is a change in the proportions of the air-fuel mixture. Detecting this contamination is quite difficult. Aerosol solvent is very suitable for cleaning the throttle.
To diagnose the injector, testers and motor testers are used. A simple and convenient device for testing the injector – Fuel injector tester ADD260. It is designed to test the performance of injectors in gasoline cars.
The tester allows you to check the performance and condition of the injectors, and then help to clean them in an ultrasonic bath thanks to special software that allows you to create various pulsations, simulating the operation of the nozzle. The tester of the ADD260 injector is connected to the nozzle and checks its operability in various pulsation modes. It is used in conjunction with a fuel rail pressure gauge..
First, they create a nominal pressure in the fuel rail, turn off the engine and turn on the tester of injectors in various pulsation modes to detect the pressure drop in the fuel rail. Such an operation is carried out on each injector and each pulsation mode. Diagnostics of the injector by the tester allows you to determine the health of the nozzle in various modes, which allows you to make a conclusion about the condition of the injector (clean injector, clogged, non-working injector).
If the tester shows that the nozzle is clogged, then it must be flushed. Now 2 main methods of nozzle cleaning are used: Flushing the injector with liquid without removing the nozzles from the engine and flushing the removed nozzles at the stand usually still add an ultrasonic bath.
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