AUTOINFORM ONLINE MAGAZINE: Diagnosing an intermittent fault on a Rover 75

AUTOINFORM ONLINE MAGAZINE: Diagnosing an intermittent fault on a Rover 75


hello and welcome to Auto inform online magazine diagnostic workshop my name is Frank Marseille and today I’d like to take a look at a particular issue of interpretation of data by that I mean how do we begin a process of repair when a vehicle has a fault it’s certainly true to say you should begin with a serial diagnostic evaluation but how do them do we react the information that that particular tool then provides us with I’m tempted to say that the diagnostic approach using SIL communication is an invitation to speculate only and by that with the greatest respect I mean that those faults stored in the computer can be caused by a whole series of events which do not directly relate to the cause of the problem in other words what I’m saying is you may be looking at symptoms not caused this particular vehicle is a rover 75 diesel 2-liter on bosch DD for control the vehicle is a genuine repair situation brought into our business with the symptoms of intermittent fairly to start there with diesel there can be many many reasons why those symptoms can bring about a no start condition I have conducted a thorough evaluation the results of which I have in front of me I’m going to go through those in a merfolk alien woman’s let’s say I’m a fuddy core logical approach looking not at symptoms but a potential cause led by those causes are potential causes I’ve attached some equipment already because we’re going to evaluate the system in two respects hydraulically using a priming gauge and electronically using an oscilloscope so the first thing I’d like to do is just review the equipment we’re using and then go through the symptoms as previously described with the sole communication extraction that we’ve already achieved I’ve attached the low pressure priming gauge and we’ve certainly used this gage many times before the advantages of this gage are that we take direct pressure measurement in our case this particular system uses a positive supply system in other words there is a positive supply electric pump fitted to the vehicle which provides positive priming pressure to the high-pressure common-rail pump so it can read directly off the gage positive pressure we also have the ability to look at the fuel flow in the form of a site block giving free and easy access to see if there’s any cavitation pockets of air bubbles or indeed any contamination so that has already been set up will almost certainly examine that to begin with now of course this vehicle has an intermittent fault the problem with intermittent faults are of course that the fault may not be present whilst a test is being conducted our view of that is you have to review the status of the vehicle only when the fault is present so we may have to conduct these tests several times so far this vehicle has not failed us and don’t anticipate the failure to happen on camera but at least the process can be discussed and demonstrated quite clearly so priming pressure is one of the things that were examining we’re then going to take a look at rail pressure interpreted electronically by interpreting the voltage path from the real pressure sensor we’re also going to be measuring current through the injectors using a Hall effect inductive clamp to evaluate how the injectors are being driven electronically as a result of that we should then quite easily be able to determine what the cause of this problem is with a no start condition but first of all I would like to go to review a serial day to have extracted then perhaps describe really how the mind is being driven to approach this particular challenge one problems with silk communication d’etre is that you have no idea initially how these faults have been stored are they’re man-made have components being disconnected are they genuine and the difficulty there is we need to take them into account but not take account of them now the faults are pre pressure control p12 sixty no pre pressure control is priming so do have a priming problem I don’t know how can we rely on the DTC well we can’t because the DTC is driven or created when the low pressure sensor mounted on the fuel filter housing reports a voltage after specification it could be a sensor fault it could be wiring fault to the sensor it could actually be a priming problem we just don’t know our view is the end product of priming is a hydraulic function and the hydraulic function is pressure and flow we go for the final function I have at this moment in time no interest in that pressure sensor I want to know what’s happening hydraulically in the system that’s the first DTC there’s a dtc relating to the cooling fan of which i have no interest where that will not give me a no start condition we have a p1e4 5 status intermittent all of these by the way are intermittent capacitor 1 voltage booster voltage to low know what that rather complex overpowering statement is trying to explain is that the capacitor which drives the injectors the operation coil with here is power driven by discharging a capacitor the capacitor is mounted in the ECU if that capacitor fails in any way the injector will not be opened and therefore the vehicle will not run so it would satisfy the conditions which we are expecting a nolan conditions that is one possibility but i don’t know if that capacitor voltage is a man-made dtc has somebody disconnected the injector and it’s installed that particular fault on this particular system if that single capacitor fails or one injector were to fail the vehicle will not run it uses the closing event of the injector to partially charge the capacitor for the next injected event so if an injector were to fail or the capacitor were to fail this vehicle will not run it will not start and or will cut out where an operation so that is an issue we need to resolve to do that we’re going to measure current the capacitor voltage is monitored thoroughly and it’s displayed as a voltage now the rule is voltage drop current down current down a volte job when we switch an injector off the voltage domitius sorry the current diminishes the voltage increases the back EMF which is displayed on the scan tool as capacitor voltage is in effect an interpretation of the current path and the quality and the quantity of the current path through the injector we’re going to measure this current end product more reliable much more accurate we’re going to measure current flow through that circuit the next fault P 1190 intermittent rail pressure plausibility controlled deviation to large another huge mouthful the number of potential cousin that are enormous three phases of common rail storage and priming pressure generation fuel delivery we potentially have a problem with pressure generation deviation rail pressure what that means is that the DRV drug regulation ventricle is a pressure control device it controls the escape of fuel back to the tank so by restricting the escape passage or spill passage pressure will increase so you will increase pressure by driving this device in you will release pressure allowing the device to open more freely so you apply more current to this to drive it in pressure increase remove current out to reduce the pressure in the rail this is controlled by duty and that’s controlled by the ECU and we’re going to monitor the duty on that valve electronically it can also be monitored serially the pump on this vehicle as a Bosch CP one three-person pump with the DRV mounted on the back of the pump so the actual escape routes back to the tank is controlled by the DRV directly mounted on the pump in some cases that device on the back of the fuel rail or the accumulator so potentially it could be mounted in that type of position not in our case in our case we have a blind rail which is what this one is with a CP one pump the deviation that the diagnostic code refers to is a deviation in the output voltage from the rail pressure sensor with regard to the duty cycle of this valve the two are monitored in closed loop very closely so when a deviation in voltage is seen it will compare the control duty and what should happen is that the correct voltage should be achieved with the correct duty command to this valve we’re going to monitor that where that’s important is that we can achieve the right voltage in the rail therefore the right hydraulic pressure at the expense of the incorrect Duty in other words the pump they have to work harder than it should to create the pressure potentially a leak or poor priming or it could be the pressures too high the valve is mechanically sticking or perhaps this get root in some ways blocked preventing a scope of the of the additional fuel which case the due to will be reduced and that is not acceptable so we need to monitor those two functions but I think first of all let’s take a look at priming storage and priming pressure generation fuel delivery in the correct order given the faults that we have always make sure priming is correct before attempting to blame the high pressure pump or potential leakage across the injectors at the moment we don’t know where the fault is but we’re going to establish or the method we’re going to establish as to directed to the cause not the symptoms what we’re looking at here are symptoms so the first port of call is priming pressure as I’ve explained this variation of system some vehicles have a pump in the tank and an intermediate pump in effect supplying positive pressure to the high-pressure pump and we can monitor this we’re actually monitoring it after the fuel filter before the high-pressure pump we’re measuring it in real time actual hydraulic pressure so the 30 needs to now is simply in fact that this particular system will prime simply by turn the key on and will provide the right pressure we don’t actually need to run the vehicle although we do have the ability with this gauge this gauge has self sealing couplings so that we can extend these hoses into the vehicle if need be and draw the vehicle on the road actually monitoring real-time hydraulic events in our case for the moment we’re doing so in the workshop so first of all what I’d like to do is just do a static Keyon test to have a look at the actual priming pressure I’ve gotten the sisters going to help me just with the various tests we’re doing we’re starting to run the vehicle but for now you can care they just turn the ignition on for me a static test and what’s up – 2.6 2.8 rebar of pressure it’s holding good their foot intermittent faults any time at all the pump could put out there could be an issue with this hydraulic pressure at the moment there isn’t the pressure came up promptly it’s holding steady there is no cavitation whatsoever within that’s not luck and I have to say in the moment I have no problems with that if I did have a problem if you can turn up with if I did have a problem without pressure the next course of action would then be to check the current to flow through the pump because I’m then want to prove is this a problem with the pump or the actual hydraulic circuit it was a pipe work block filter or whatever by monitoring current flow through the pump that also helped me predict whether it’s a pump fault or not but at the moment I can’t fault it there’s no point me doing their checks with regards to current through the pump so that part of the test now for now is finished and leaving the gauge attached so keep an eye on that at all terms and we’re doing other further testing but apart from that that test is finished one the other DTC’s I mentioned was real pressure deviation now the real pressure sensor is a 5 volts device three wires output power ground in most cases not in all but in most cases the middle pin is the output I’ve connected a probe a acupuncture probe into the middle pin it’s a 5 volt device it is fed with 5 volts has a ground reference through the ECU and its return circuit will then report the theoretical hydraulic pressure against voltage there is what we call a plausibility value of 0.5 a volt keon 0.5 so we’re going to go through a series of tests now whereby we turn the key on static we’re going to look for 0.5 we’re going to crank the vehicle and observe the pressure rise against voltage source a voltage against pressurized we then go to oil the vehicle to idle for short period of time to look at stability because deviation means that the pressure against voltage is wrong and that could be a sticking the RV deviation it’s mechanically sticking because the pressure sensor and the DRV work very closely in where’s lewb they each monitored very very carefully then we’re going to open the throttle wide open do a simulated high-pressure test back to that Riedel and key off and that profile test that we call it then will give us an awful lot of information about the functionality of priming pressure generation and to a point fuel delivery which is it the job of the injector finally when we’ve done that we’re then going to attach the current device on to just 1 injector we will of course test or four injectors but initially just for the purpose of the filming – one injector and monitor the actual current flow through the control solenoid so would like to do first of all this set the scope up before we start the vehicle or anything the first channel and the check where we’re connected the blue channel is connected to the DRV summer blue probe is connected to the control circuit it’s this is a ground control device which means it’s ground switched on on means in in means higher pressure so the higher the duty the more the pressure and monitoring that duty with the scope on channel one now all devices which use movement as a function will use nominal battery voltage so I need a nought 220 volt range I’ve already set the range you can see of an infinite adjustment of range 20 volt range has been set on channel 1 channel 2 red is on the middle pin of the rail pressure sensor voltage so 5 volt device so I’ve set a 5 volt range current I’ve not yet set up now we use voltage for current it’s quicker and more practical we turn the whole effect inductive pump arm to a 20 amp range these injectors will use about 18 amps of current so a 20 amp range and this equates to a hundred millivolts per amp which means if ice at 10 amps per volt so if I set a 2 volt range that gives me a 20 amp span which is what I want and the conversion is straightforward forums 8 amps 12 16 20 amps I don’t really need to call it currents it means I can very quickly then remove this clump and replace it with a voltage probe if I wish without any changes to the software so it’s a pure economic workshop way in which we we operate however it does want zeroing as a slight deviation so push the zero button we’ve now set the zero baseline at zero that’s ready to attach to an injective that we can attach it now I don’t know which way around this needs to go yet so we may have to change that and I’m just going to take a guess as to which way around it girls if the current is inverted down of course we want to reverse a clump and get it in the positive direction wrap the scope is set up the first thing we could do is actually turn the key on without starting the engine because we’re going to see a couple of things which will be interesting and worthwhile monitoring so you Keyon but don’t start please rap I’m using a short time base why because I want to see the actual control events all we’re looking at there is the control event to the DRV it is permanently fed with power and is ground switched through the computer so ground is the on the event and you can see from that that it is more off than um and roughly 75 off 25 on their correct duty for this vehicle running at idle is around 18 percent on from this valve with 1.3 volts from the rail pressure sensor which equates to 300 bar that’s the balance I want to see the actual rail pressure voltage in red should have a plausibility value hey kyon static as we are now of 0.5 of a volt I can measure it with the cursor or with the marker and if I left mouse channel be read 5 1 8 millivolts that’s near enough so the plausibility voltage static is correct help port power ground therefore must be correct the next stage now is to increase this time base to provide enough time for us to go through this process of cranking starting etc if I do that and I want about 50 seconds so if I change to 5 seconds per division with a 10 grid screen that gives me 50 seconds you can see now that those control events have been compressed into an envelope and what we get is a broadband so we can no longer actually use that to any value so for now I’m going to turn channel 1 off and we’ll come back to that later so all we’re interested in at the moment is looking at the voltage from the rail pressure sensor during this this profile testing technique so I’m just going to wait until it’s passed across the screen unfortunate when we use this screen it denies me access to the keypad for a stop and start so we’re just going to allow that to continue across the screen and then we’ll begin our test very shortly as I said we’re into a whole series of tests not just to see what the voltage is but also how quickly the voltage changes in respects of crank you’re starting and full-throttle so if you can get ready if you turn the key off to begin with please that’s the system part two up key on static do not crank there’s your half volt crank and start do not revolt both righto and up there we have a full profile I’m also waiting just to allow the decay to take place and now these years turned off okay what we need to do now is review the data the green image in the background is the current through the injectors the clamp is the right way around the currents going positive which is good I’m going to remove that part of the analysis for the moment and concentrate just on this rail pressure we’ve established 0.5 of volt Keon static that’s fine I want to now look at this section here this is a section where we crank and start the car and in particular I want to look at the rate of rise I want to look at the value that’s voltage against pressure and the rate of rise what we should say is about one point four volts which is a little bit too much we’re expecting one point three three hundred bar being brought under control by the ECU and that looks as though that’s being achieved so the first thing is to measure the voltage and then the rise time this system should create three hundred bar in well under one second of real time so first of all let’s use the cursor and we’ll take an average of that voltage event 1.5 volts and that’s well over 300 bar so there’s nothing wrong with the pressure created during the cranking process and now the rise times we use a horizontal and the vertical curtains I should say and I’m going to take a mean average also when that pressure was achieved 675 milliseconds that’s just under point seven of a second that’s excellent there is nothing at all hydraulically wrong with this system the priming system is working the high-pressure system is working in fact that wouldn’t work if priming wasn’t working we know priming is working we’re monitoring that there is nothing wrong with that we no need to challenge their system on load which is the acceleration test so the next part of this assessment is to look at this part of the test I want to look at the maximum value voltage achieved this can vary from system to system but this particular variation Bashi p1 dd4 should create in excess of 4 volts peak voltage when the engine is revved up statically so back to the horizontal cursor looking for a peak value somewhere around there it’s quite a bit of noise noise is actually created and caused by the injectors and of course it compresses so I’m going to take a mean average of that part of the signal and it’s 4.16 for so it’s well over 4 volts it’s a 1350 bar system 4 volts out of 4 and a half for the half volts is maximum pressure well well it will well above a thousand bar pressure so once again the rate of rise is very aggressive well well over a thousand bar or around a thousand bar pressure so hydraulically there’s nothing wrong with this system that further challenges priming of course because the whole pump has to work harder and the rate of rise will take a plot because this is now at 300 bar at idle and I’m also going to take a mean average of the maximum pressure and that’s taken 1.5 seconds there again I would quite happy with it the results I’m happy because of the the profile one second would be nice it’s a little bit over that no problems at all with the shape and profile of that equally when we left off want to watch it smoothly achieve the 1.3 volts let’s just check that at its 1.3 volts on moving the horizontal cursor down 1.38 to excellent and you can see that when it was at idle we then expended the full throttle test it’s returned perfectly back to 1.3 volts out also means that this device which it has to close dramatically closed to achieve that pressure up then has to in effect dramatically open to bring this voltage or pressure back on the control if this was sticking mechanically you would have deviation it would struggle to achieve that closed loop control it hasn’t so back to the full image and I’ll remove the cursors but we’re finished with that part of the measurement so you can see from the overall view stabilization of precious good cranked start build up is good full throttle is good decay can be assessed the time it takes for the pressure in the rail to diminish back to 0.5 which is zero pressure point five does not represent a pressure at all it is a zero and you can see from that it’s taken about five eight seconds or so of time to diminish Bosch CP ones around then are seconds so I don’t anticipate any internal leaks either so really what I’m saying is this system at the moment is perfect there are no faults with this vehicle which as frustrating as his this is the real life the process is good there’s nothing wrong with process we now have to wait till the fault actually demonstrates itself however we haven’t looked at the injectors that was a separate DTC which potentially could be the course if you recall what I said was if an injector coil were to fail or the ECU capacitor were to fail then it will not drive the injectors the vehicle will cut out and or not start the capacitor voltage referred to is the voltage that you will read through a scan tool 60 to 80 volts ideally near the 80 Volt mark remember the rule current down voltage up we’re measuring the induced voltage into the coil when the current path is interrupted we’re measuring current that’s the current path of the injectors one injector so if I slide the voltage up I’m going to zoom in to very tight area these injectors work on the principle of two events pilot a main which I’m going to zoom into in a moment and this event here is an extra event which takes place to top up the capacitor in order that that capacitor is charged sufficient lector open the next injector event which is why if one injects were to fail that won’t happen therefore the next injector opening event will not happen so let’s just zoom in spill further and further again now we’re now looking at pilot and the main fuelling event current which is a real event in other words it takes into account by measuring current we take into account power supply which is a capacitor and the ground reference through these see you we have one point eight seven volts that’s eighteen point seven amps over the top of the page and we’re making very much very close that figure so we made we make in above 18 amps of current flow there is nothing wrong with the driver circuit to this injector and therefore I am satisfied that the coil and ECU and the wiring and the capacitor and the ground are all good that’s on that injector we do of course have to and test each individual injector and or wait until the failure occurs to determine if one particular injector has failed so I’m just referring back to VT C’s it just say intermittent capacitor one voltage so it’s not actually detected a particular injector circuit it’s just said the capacitor one voltage booster voltage too low what it’s actually saying is not enough current flow through the injector that could be about earth could be bypass applied to these see you it could be somebody has just unplug the injector and try to start it there won’t be any capacitor voltage therefore it’ll be too low so I’m happy with that and you can see a whole range we can see the frequency changes well do when you rub the very clip you get so much higher frequency you can then see that on overrun when you do not require fuel the injectors are turned off and they come back on promptly to enable the vehicle to idle again so there’s nothing unusual there and if we look at this little bit here the other interesting fact is that this system will not start until one volt is achieved in the rail pressure sensor and if we look at the rate of rise here and we look at the first injected event I bring the two together so I get this quite accurate so the first injector event has took place at one point one seven six volts and you can see that the noise there’s an absence of noise here no injector and the first injector noise spike occurs there which is caused by the opening and closing of the injector the high current flow occurred at one point one seven six so that the system is behaving impeccably if you don’t make one volt it’s ain’t going to go so analysis complete there’s nothing whatsoever wrong with this vehicle the process is perfect in its construction all we now have to do is to wait for whatever is wrong with this car to occur and we’re ready tomorrow Tresor quite simply and we’ll have to discuss the options with the customer continue testing until such time as the vehicle cuts out I will attempt to find out if there’s anything else that’s perhaps relevant to their vehicle not starting temperature hot weather cold weather moist whatever does it happen static does it happen when the vehicles driving does it happen after a period of driving I need some more information now I have all the technical information require all the measurements are need to establish what causes not symptoms these are symptoms and they’ll need opportunity and opportunity as a car to break down so I hope this has been of some interesting you see how we intuitive about the tests we do the process procedure and how we interpret these events not being led by DTC’s but being led by the potential causes of these DTC’s and hopefully you can apply this principle to any form of diagnostic process that letter thank you for joining me and I look forward to meeting you again in the next edition thank you very much you


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