Frank Massey’s Top Ten Tests with PicoScope: #8 Direct fuel injection – high-pressure pump testing – Howtoshtab – how to, lifehacks, tips and tricks

The next example I have chosen for using a scope for dynamic systems testing Relates to direct petrol injection high pressure pump performance And I have to say it is identical to common rail in certain concepts Certainly in principals of operation it is So I have chosen this because it is a slightly different take Pressures are different performances are slightly different And once again it is very focused because we now have an incredible number of Direct injection engines well they all are now The objective is to understand the importance of rise time Maximum pressure and pressure hold Skill sets To interpolate function of electronic control unit and hydraulic Pump performance of pressure over time So here we have a direct petrol injection system The Bosch variants which I am more familiar with than others Although we do work on many direct injection systems Operate by one or two principals either by volume control or pressure regulation So we need to try and predict which it is now there is an obvious answer to that There is a singular control device on the pump If you unplug it and pressure goes up and it is a fail open device Then it is volume regulation If you unplug it and pressure drops then it is a pressure regulator device DRV And this example is exactly that If I were to unplug that device pressure drops And the engine will run on pure priming pressure which is six bar And the injectors open more It is an inductor it is a coil it is a solenoid So it requires current and it requires a drive signal So I have put the probe in the control signal Because I am going to take control over that event again It is ground on but I want to prove it to you that it is ground on So we need to establish if it is ground control or power control So I will do that first I am also connected to the high pressure sensor Very much like common rail three wires output power ground The range it operates over is of course different to common rail Because the pressures on this engine are somewhat different The general range for direct injection is 50 bar at idle to around 130 bar on full load However there are some systems now approaching 200 bar And I can assure you there is development taking place I have spoken at length with Roger from Aznew Who has forgotten more about injectors And Phil than I will ever know And they are discussing research taking place where they are talking of 1000 bar Delivery pressure for future applications So things are moving all the time So on with the oscilloscope Inductor voltage 0 to 20 Volts on the actuator Low voltage on the sensor 0 to 5 Volts with an active range between 0.

5 and 4.5 And that is it they are the only two measurements we need to make So let me run the car and we will talk about the setup on time and voltage Triggering we do not need any it is all done in free run First of all This particular time frame is my home page I have altered voltage ranges So what you are looking at here is Real pressure in blue And the control event to the actuator in red So let us just have a look and shorten the timebase to 1 ms Let us see what that produces for us An erratic signal in free run Tell you what let us apply a trigger to channel B just to see what is going on So channel B We want a repeat trigger on B Scopes blind Once again poor application of trigger and scope is blind I have already had a preview so I know where to go and hide the trigger threshold So we need to adjust the offset That is the offset down here Now that is the control signal to the actuator which controls rail pressure And you can see it is a reasonably complex signal not just on off Where there is a change in duty This I suspect is a change in both duty and frequency So not quite as easy to predict how that should respond Now what that is controlling in reality is current Current is what moves that actuator in and out and determines what the pressure is Before it is released from the rail Now is that a power on device or a ground on device Well let us go to the other side of the actuator and take a look So I need to turn the trigger off Trigger off in free run Let me now move the probe over to the other side And we have a fixed power line at nominal battery voltage Or regulated alternator output voltage Let us change the scaling to 20 Volts There we go that is better So we can see that the power supply remains stable Where as the other side of the actuator has this event on it So it is a ground on control that is all I want to know So I am going to remove that because what I want to do shortly Is take over control now we know it is ground on And I am going to become ground But I do want to be damned sure before I do any of this kind of testing That I am the right side of the circuit which I am now confident we are I can now manipulate ground Therefore increasing the current flow through the device Slamming it shut we should build up maximum pressure from this system It has no where else to go We are monitoring rail pressure so we are now going to be looking at Rise time and pressure hold In other words does this system have hydraulic integrity the ability to hold pressure Because similar to a lot of common rail systems this system should retain pressure semi indefinitely That is a very useful test So let us begin first of all by looking at profile So what do I need for profile I need more time So we are now looking at rail pressure over 50 s of time I am going to increase the throttle and then switch the ignition off Ignition off and back on as I want the sensor to remain active And I can actually leave this scope running for quite some time You can see a very slight drop in pressure very slight But on a semi indefinite basis that pressure will be maintained in the high pressure rail As you can see it is stabilising That is good news because there should be no return with this pressure So that part of the test is successful let us just freeze that frame And go back to the first part of the frame So at idle we had that voltage which represents the rail pressure voltage We opened the throttle so we can look at rise time And we can zoom into that even more accurately if we wish You can see that the increase in pressure in the high pressure pump is continuous It does not represent full system pressure although it is quite close But is does give us an indication of how quickly it rises So let us just see how quickly that pressure came up Operating the throttle To a peak value It is just under 1 second 971 ms about 1 second in rise time It is not a pressure we are going to do that next Does it represent good control pressure Well for this particular variant of pump yes it does If this was an RS6 or I have the 280 Cupra which produces a very healthy Out put in terms of power then the rise time from that Later generation of pump is much quicker than this But for this particular variant that is perfectly OK That just under 1 s of rise time is good And it is holding pressure once we switch off which is also good I would really like to challenge this pump fully By taking control of the high pressure pump The minute I do that of course it is going to go into default as well So let us run the scope You may notice that after all this talking I have been doing we still have 2 V in the system It is there on a semi indefinite basis I have no idea how long that lasts but it is an awfully long timebase That is one of the most important checks because if you have Dribbly injectors or the pump is leaking on the spill circuit as there is one on this pump Then that would be an issue for us and that clearly is not the case So let us run the vehicle and do a proof test This represents the ground control side of the actuators Engine is running normally Scope is in the right position on the sweep I am going to hold it on ground You will hear the pump squeal And off And off with the ignition Now the default has beaten me to this test I think if I am going to get any more pressure out of this pump I need to increase the engine speed Because we came in at correctly regulated pressure around 50bar I shorted out the actuator and it did create an increase in pressure And then went into default because if you notice there we are still measuring real pressure We actually then dropped pressure in the rail down to this value here which is default So in other words we have lost the operation of the high pressure pump We are running purely on primary so two things have happened The primary circuit takes over the supply of fuel into the pump into the rail And the injector opens more to deliver the correct amount of fuel to maintain Lambda 1 So we can take a look at rise time and you can see that under extreme stress We did not meet full potential but we got two thirds of the way there But the important thing here is that you have a rise hold rise hold rise hold Quite often when these pumps start to go wrong what you get is a rise and then a drop Then a rise and a drop which means that the pumping elements inside the pump Have started to become leaky which means the rise time has increased And the ultimate maximum pressure is compromised That is not happening with this pump So once again it is an incredibly accurate way of testing the pump under real time conditions With fuel in the system and just to confirm it has gone into default Now course to compliment this test we would also have a Low pressure gauge on the priming circuit monitoring things like flow and pressure In that circuit as well and of course we would also measure current through the priming pump Remember when dealing with a pump it is Pressure Flow and Current consumption When both of those are present and the proof test to prove that When pressure goes up current also increases Which should have taken place with particular this priming system So very similar to the common rail in terms of its function and objective It is to prove the hydraulic functionality of what is a hydraulic pump controlled electronically yes But nonetheless it is the hydraulic functionality that we are adapting the scope For an incredibly accurate test So once again it is very accurately confirming what the nature of the fault is And how we would progress in its repair.

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