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The first production cars with this system, developed by Bosch, appeared in 1996. It owes its name to a single ramp, from where the fuel goes to the nozzles. The main advantage of the system is a sufficiently high fuel pressure in all engine operating modes, which contributes to better mixture formation in the combustion zone and complete combustion. Preserving the moderate appetite of its predecessors, the CR diesel engine better meets environmental standards, and such a car is often more dynamic than a gasoline one and almost as quiet.
The heart of the system is a high-pressure fuel pump, a compact device with one, two or three plungers and a mechanical drive. The body of the injection pump is made of aluminum alloy, the plunger sleeves are steel. So that at idle and at small loads the pump does not drive fuel in vain, on some three-plunger ones one section is automatically switched off, and two-plunger are regulated by metering devices. The fuel pump itself is supplied to the fuel pump from the tank under a pressure of 6–7 bar by a booster pump. He is either gear
chaty and built into the body of the injection pump, or electric - in the fuel intake module or in the highway.
Injector repair kit
Injector repair kit. Injector repair kit.
Already in the crankshaft scroll mode, the high-pressure fuel pump starter creates a starting pressure of 350–400 bar. At minimum idle speed - up to 500-600 bar, and at maximum load - up to 1300-1500 bar. There are pumps with pressure up to 2000 bar. Its value is set by the regulator located on the high-pressure fuel pump housing or on the ramp and subordinated to the electronic engine control unit. Issuing commands, the computer relies on the signals from the pressure sensor in the ramp.
Through high-pressure pipes, fuel is supplied to nozzles opening under the influence of an electric signal. There are two design options - electromagnetic or with a piezoelectric element. The first at first did not differ in speed, which forced the designers to look for an alternative. In a piezo injector, voltage is applied to the piezoelectric crystal, which instantly expands. The spool compresses the spring, the nozzle needle opens the way for the fuel - and it is injected into the combustion chamber. However, designers continue to improve electromagnetic devices - both options work successfully on modern engines.
A modern nozzle is a compact but complicated device
A modern nozzle is a compact but complicated device. A modern nozzle is a compact but complicated device.
About how thoroughly the experts brought the diesel engine's workflow, its low noise says. So, pre-injection before the main dose significantly softened the ignition of the mixture - this alone made CR diesels more silent than their predecessors. There are CR and “post-injection” diesel engines. Its official role is to clean the particulate filter. An additional portion of fuel, without burning in the cylinders, enters the filter and heats it to temperatures at which soot is completely burned out.
DIAGNOSTIC
There is a minimum of equipment, without which it is unreasonable to start work. Diagnostics of electronic systems begins with reading fault codes, checking sensors, actuators. There are no special diesel scanners, there are universal ones, that is, for a wide range of cars, or dealer ones for a particular brand. To study the signal from the device under test, you need an oscilloscope. But it is expensive, it’s more profitable to buy a scanner with an additional oscilloscope function.
Fuel pressure is checked by pressure gauges. Low - mechanical, with a scale of up to 10 bar, and high - a special device with adapters and a range of at least 2000 bar. And to measure the amount of fuel drained from the nozzles, you need your own set.
The troubleshooting algorithm depends on the nature of the failure. If the engine does not start (electronic locks and forgotten secrets do not count), we check the timing drive integrity. If the starter rotates the crankshaft with effort, this is not bad for the owner, but if without resistance, repairmen will be happy: the work ahead is expensive. After all, diesel engines are “plug-in” - when the timing drive is destroyed, the pistons bend the valves, and then how lucky.
Stand for testing injectors and high pressure pumps
Stand for testing injectors and high pressure pumps. Stand for testing injectors and high pressure pumps.
If the timing drive is in order, go to the fuel supply check. The electric booster pump comes into operation by turning the key. When this pump is worn or damaged, the power consumed by it changes, the computer records this as a malfunction and writes its code into the system memory. But you shouldn’t completely rely on electronics, so we connect the manometer to the low-pressure line. (The mechanical booster pump has a fitting for ease of control.) If the pressure is normal here, go to the high-pressure pump.
Check the fuel pressure in the ramp in the crankshaft scroll mode with the starter. This part of the system is equipped with a fuel pressure sensor - we will use its services. We connect the scanner to the diagnostic connector and find the desired parameter. If it is below the norm, we are looking for where the malfunction is hiding. Blame can be nozzles, solenoid valves (regulators) and the injection pump itself.
The scheme of the diesel power system "Common Rail":
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1 - fuel priming pump
2 - fuel filter; 3 - fuel injection pump
4 - dosage valve; 5 - sensor
fuel pressure; 6 - fuel
ramp; 7 - pressure regulator
fuel; 8 - nozzles
REPAIR
Only a specialized workshop can restore the pump’s working capacity with qualified personnel and diagnostic equipment. The repair cost is from 7 thousand rubles. Further depends on the complexity. For some damage, it is wiser to buy a new fuel pump. The usual price, about 30 thousand rubles, shocking the fugitive diesel engineer, because in the course of the repaired or restored products.
A high mileage CR diesel engine can often not be started up due to a malfunction of at least one of the injectors. A fuel leak through its valve does not allow the pressure in the ramp to rise to starting values. To check the pressure at start-up, there is a special diagnostic kit. It includes a control pressure gauge, a pressure sensor, tubes for connection, plugs instead of actuators, and measuring tanks for backflow.
Injection pump with cut-off valve for the plunger section
Injection pump with cut-off valve for the plunger section. Injection pump with cut-off valve for the plunger section.
It is wise to replace worn nozzles with a kit. The price range is very large: depending on the model and manufacturer, they cost from 8 thousand to 25 thousand rubles. a piece. The characteristics of each new injector must be recorded in the memory of the engine control unit, because there are no two injectors with the same performance. Different not only affects the uniformity of the engine and its dynamic loads, but also affects the performance of the car. Although every ECU has dynamic adaptation (constant adjustment of the cyclic fuel supply for uniform engine operation), it must be remembered that it cannot replace the encoding if the latter, for example, was forgotten to be written.
The problem of difficult start-up of a diesel engine is one of the common ones. And the owner is sometimes dissatisfied, for example, with reduced engine power or exhaust smoke. These problems are the most complex, because they require an assessment of the accuracy of measuring air flow or boost performance, the efficiency of the recirculation system, the exhaust system, including a particulate filter (DPF) and a catalyst. However, now these technologies are perfectly mastered by the masters of diagnostics.
