In today’s article we will talk about a very important component of the injection system, namely about the high pressure pump. Most drivers have certainly heard of the high pressure pump (or “high” as it is also called), but we are sure that most do not really know what this pump does, how it works, what can break and how we have to protect her.
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You will find out these things if you read the article carefully to the end. Let’s not go too far and draw directly to the subject, the high pressure pump is part of the injection system of newer generation engines that use the CR injection system (common rail, i.e. have a common injection ramp).
To better understand, I will explain for the first time how the common ramp injection system works. This injection system is much better than the classic one (pd- shower pumps) because the fuel injection is no longer dependent on engine speed and load, so it can be much easier to optimize the injection (time and amount of fuel injected into the chamber combustion) for each engine operating point.
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In the case of common ramp injection systems, the injectors are connected to a common ramp (as the name implies) and not directly to the pump. This means that the fuel pressure is independent of engine speed and load, so if the on-board computer commands the injectors to put more diesel into the combustion chamber even if the engine has a fairly low speed, they will do so because they are always kept under pressure, regardless of engine speed.
This independence from the engine’s operating point has many advantages, the most important being high performance and lower consumption. For those who have more knowledge of mechanics, this system can also divide the fuel injection into several phases, namely pre-injection, main injection and finally post-injection.
The amount of fuel injected into the combustion chamber is controlled by the on-board computer after collecting more data from a multitude of sensors. But it is mostly influenced by the position of the accelerator pedal, depending on how hard or how suddenly you accelerate, the more the ECU will command the injection of a larger or smaller amount of fuel.
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No matter who they are made of, these injection systems are electronically controlled by the ECU, sensors and several solenoid valves. We need to know that this injection system is a bit more complicated thanks to the fact that it is controlled by many electrical components such as: injection computer or ECU, camshaft position sensor (to know exactly when the fuel must be injected into the chamber burn), engine speed sensor, accelerator pedal sensor (so that the ECU knows exactly how much power we need and how hard we apply the engine thus determining the amount of diesel injected), ramp pressure sensor (it has the role of measuring pressure from ramp, for the ECU to further control the high pressure pump if additional pressure is needed) and a few other temperature sensors and flow meters.
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From a “hardware” point of view, the common rail injection system consists of: air flow meter, injection computer, high pressure pump, common injection ramp, injectors, speed sensor, temperature sensor, diesel filter and accelerator pedal position sensor.
Well, once these aspects are established, it’s time to focus more on the high pressure pump. For the common rail injection system, diesel has the following route. It comes from the tank at a very low pressure (normal, somewhere at 1-2 bar) and enters the diesel filter to be purified.
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From there it comes out with a slightly lower pressure (around 4-5 bar) and reaches the high pump through low pressure hoses. From here things get a little complicated because the high pump “pushes” through a special pipe diesel in the injection ramp with a very high pressure, a pressure exceeding 1400 bar that can reach 2500 bar depending on the model.
The high pressure pump, as the name implies, ensures a high fuel pressure in the ramp regardless of engine speed. This pump is engaged by the crankshaft of the motor with the help of an accessory belt or depending on the model is mounted on the belt or timing chain.
But the advantage is that this pump does not have to be adjusted in the sense that it does not have to be set up as required for conventional injection pumps. These older generation pumps are limited to 3000 rpm. The diesel is sent with very high pressure to the ramp from where each injector is supplied.
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At this type of injection, the injectors work more or less like “taps” that simply allow a certain amount of diesel to pass at a certain time.
The injectors are electrically controlled, which is why problems can occur over time. What would be the disadvantages of this system? Well, for a start, it works with a very high pressure, ie the tolerances inside the high pump and not only are very low.
The electronics are at home, everything is controlled by either a sensor or a solenoid valve, nothing is more mechanical, everything is at least electrically assisted.
When the pump fails, it produces metallic foam that contaminates the entire supply system, the foam reaching the tank. Worse is the fact that the injectors will lock. Depending on the material from which the span is made, we can figure out what exactly yielded in the high pressure pump.
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If the chip is made of aluminum then most likely the bearings inside have started to “exfoliate”. If the foam is very fine, in the form of extremely fine filings then we have some wear and tear on those pistons or to the system that pumps fuel with pressure.
How do we know this pump will give up ? Well, most likely when it fails, it will not be able to create the necessary pressure in the injection ramp first, so it will most likely occasionally turn on the engine indicator light on board and cut off the acceleration pedal.
The car will start to do so more and more often, especially when you accelerate suddenly and very violently. In the end, the pump will give up completely and the engine will simply not start. If your high pressure pump fails, you should know that you have several repair options.
For example, you can buy another new high-pressure pump with a warranty, but it will cost a small fortune. Some people resort to the option of buying second hand , from dismantling, which we do not recommend to do because you may have the misfortune to come across a pump that did not have a very easy life.
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The best option from our point of view would be to recondition it, there are many specialized services that can recondition your old high pressure pump at much lower prices that you can afford.
A disadvantage if we can say so is the fact that when reconditioning the high pump, the workshop that deals with this also wants to recondition the injectors, to clean the ramp and the injection pipes.
Some say to clean the tank and the route because if the pump starts to span, then the whole system, including the tank, are contaminated with iron filings. After installing the freshly reconditioned pump, it will span and fail. For this reason it is good to perform these operations.
So you better try to use quality fuels, not to refuel from any canister and to change the diesel filter in time so as not to end up in this very complicated and expensive situation.
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