AUTOiNFORM ONLINE MAGAZINE: DPF regeneration in vehicle diagnostics with David Massey

AUTOiNFORM ONLINE MAGAZINE: DPF regeneration in vehicle diagnostics with David Massey


hello and welcome to inform online magazine my name is David Massey and today he’s diagnostic workshop feature he’s talking about DPF regeneration first of all I want to introduce this car and give you a little bit of background to what the problem is and what it’s doing and the customer brought the car to us with the complaint of poor fuel economy but mpg reduce engine performance and intermittently a rough idle speed of course first thing we always do is check the fault codes this car didn’t actually bring back any fault cards whatsoever knowing the system pretty well and with experiences what we’ve had with DPF filters the first thing I decided to look at was DPF engine data new emission law euro-5 what currently it’s getting tighter and tighter in order to maintain these strict emission laws the introduction of DPS has been introduced and we are seeing increased amounts of problems the amounts of soot and mass of carbon buildup in the DPF filter it’s primarily caused by poor internal combustion obviously there can be many reasons for this but the primary reasons which we see in the workshop is down to quality of fuel being but we also see a lot of DPS blocked that has had extended life long service history shorts unlimited drivability they saw contributes to a buildup of ash and massive salts in the DPF filter ways we can combat this is by preventive maintenance is my favorite way using good quality fuels a high quality of oil and we also have a new breed of engine flush treatment we use and oil additives so the first thing we always do when we diagnose these systems is look at basic sense of plausibility in order 50 PF to regenerate itself it needs to know certain data from sensors on the engine the two main sensors in question in this case are the differential pressure sensor and exhaust gas temperature we can check these very very simply by looking at live data and I’ve actually pre-selected the engine group data for ease but if you go into group 100 column 3 & 4 you’ll actually see the differential pressure therefore you very simple plausibility test on this system is to have a look at differential and pressure with the ignition on so engine not running ignition on you should have a value of 0 or slightly minus figure if we have a look at this straight away there’s a problem we’re actually showing 50 milli bar with the ignition on and it should like said it should be zero so this system will not be able to regenerate itself efficiently or properly until we repair that sensor how I intend to go about fixing this problem is two methods replace the sensor number one recalibrate the sensor using this direct scan tool and once I’ve carried that out due to the previous nature of this car and with a long life servicing the poor drivability extended oil changes I’m going to flush this engine both in the engine oil in the manifold and get rid of any deposits this chemical process can also help the DPF regeneration procedure we’ve had some excellent results from that so that’s how we’re gonna tackle this problem and just going back a little bit talking about two different types of DPF filter there are there are what I call close-coupled DPF filters or those additive filters and the VA gene German group decided to use close-coupled what it’s doing is actually using the excessive engine temperatures of 300 and 350 degrees which we achieved at motorway to help regenerate DPF filter all the systems which use are additive DPR filters which are halfway down the car and obviously we’ll see a much lower eg T’s or exhaust gas temperatures the only way it can help regenerate those filters is about used as an additive these systems can prove unreliable to different types of regeneration process there are passive process or active main difference in the two is that passive regeneration will take place on a normal driving circumstances you’ll never notice any change and drivability or performance of the end on the motorway you’ll see exhaust gas temperatures anywhere between 300 and 350 degrees say if you drive the car around town I sure distance you will only see temperatures and exhaust of 150 to 250 degrees this is not enough the DPF to regenerate and get rid of any of the buildup in the exhaust so this is where active regeneration comes into play what the ECU does is actually targets the exhaust gas temperature much higher it does this by always shorts EGR valve off introduces an extra injection cycle after the main injection process is taken place shuts off the air supply to the engine partially through an electronic flap and the fourth and most significant increases in boost pressure this will actually help compensate for lacking power and poor drivability as a driver you may or may not actually notice this taking place but when this does take place you will see exhaust gas temperatures in excess of 600 to 700 degrees C this is when the regeneration is taking place it’s helping the the coating in the DPF and turn the harmful deposits such as hydrocarbons carbon monoxide sulfur dioxide and carbon molecules into carbon dioxide okay before we undertake any forced regeneration procedure and we’re going to quickly recheck the differential pressure with the engine running at idle and we’ve now replaced a faulty sensor and then we’ll have a correct correlation our idle showing zero millibar so we expect to see an engine with DPF idle value no more than 30 million bar mmm we’ll have a look what we’ve got here it’s recorded the differential pressure at 60 millibar that is way too high more than double what it should be at idle so I’m confident now that the compression readings are correct and the canal go forward and carry out what I call false regeneration procedure as well as doing a force region we’re going to do the flush treatment the chemical treatments and helping clear up the combustion problems which would cause DPF blockage so what we’re gonna do now is kill the engine and carry out the flush process and force regeneration okay welcome back and what we’ve done is carried out the three stage flush treatments what you’ll see appearing on your screen now is before and after pictures before the flush treatment was carried out as you can see the difference it’s made in removing the carbon deposits its carbon deposit it’s obviously an EGR valve in the manifold and the valves not to mention the DPF filter so the cleaning process is quite an aggressive one and it’s also worth mentioning as well that if you watch the the previous diagnostic feature using the BG flush system you may have noticed quite a bit of diesel not beauty you’ve modified the the size of the jet now which is completely eradicated the diesel not problem it uses a smoke smaller jet and produces a much finer mist yes the process takes longer but there’s no diesel knock and all right moving on to the results now what we’ve found if we have a careful look now the particulate filter difference in pressure before if you remember about 58 million by now the engine running at idle that’s exactly what I want it to me about seven million by it’s more than acceptable so the flushing works the regeneration has worked and obviously the new sensor with bit is now giving the correct reading so I’m happy now that this car is it’s fixed it’s sorted I’m going to give it back to the customer with obviously fresh oil new filter and a flush treatment in the tank I may invite them back in a week of time so just to evaluate the the prep here make sure I’ve been okay with the car and obviously close to the model to the fuel consumption but you know having repaired lots of these systems now in this method I’m fairly confident as well coming back and if you are interested in developing your diagnostic skills any further and please visit our Altima for website more details of our face to page training thank you very much


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