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Frank Massey’s Top Ten Tests with PicoScope: #8 Direct fuel injection – high-pressure pump testing


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

6 thoughts on “Frank Massey’s Top Ten Tests with PicoScope: #8 Direct fuel injection – high-pressure pump testing

  1. A good idea would be to use a bit higher resolution, you can barely see what is on the screen and that is very very sad… As always, Frank is an expert and sure know what he is doing – no doubt! Please PicoScope Automotive, better resolution, thank you!

  2. OMG I never realized how much easier it is for you guys in countries with RHD vehicles to walk over and start the car from outside the vehicle.

  3. Hi, with the engine running and at idle speed, is it normal to have an installable pressure that varies from 35 to 50bar?

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