Doctor Diesel

Magic Mazda update

Hello again, Doc,Well, wheels have rolled, and my fuel pump has sucked and squirted another tankful of diesel through my Mazda2’s engine, so itís time to take stock again. In fact, wheels have rolled well, this time around, to the extent of a pleasing 728 miles between fill-ups. With my on-board computer (OBC) saying I had just five miles of fuel remaining, I replenished the tank with 41.87 litres of Esso diesel, indicating, by my calculations, a fuel consumption of precisely 79mpg, the best that I have seen so far. I am feeling pretty smug, so no doubt my comeuppance isnít far away! The figure may have been boosted this time around by my carís strange reluctance to drop into DPF regeneration mode, and during this tankful I identified only three regeneration episodes, at intervals of 191, 347 (remarkable!) and 178 miles. I cannot explain this change of behaviour, but it is a welcome development, if it is permanent. Just thought Iíd keep you posted. 


Best wishes, Bill Lawrie


Hello Bill,


Very interesting. I could speculate about the possible beneficial effects of (much) warmer weather, and thus possibly more natural regeneration, and also less primary generation of particulates, with the engine warming up much faster, and running hotter, but that is pure speculation. As a matter of interest, I have discovered recently that some DPF-equipped engines (that’s all of them, these days!) are programmed to regenerate regularly, regardless of the pressure drop across the DPF (in other words the soot loading in the filter) at regular intervals. Some, I know, are simply mileage related, whilst others may use the ECU to monitor running conditions and make a calculation as to when to initiate a regeneration, much as they do with variable oil change intervals determined by the ECU. If you could be bothered, you could try and monitor, say, average mph between regenerations, to see if there was any correlation with the distance between them. 


I presume that you are sticking to the same fuel brand. I will try and dig a bit deeper into the matter of programmed regeneration though, and let you know if I discover any more interesting facts. Here is an extract from a technical information/instruction file on the subject, relating to the current Volkswagen EA 288 engine:


ìMileage Regeneration: The ECM (ECU) automatically initiates an active regeneration if there has been no regeneration, or no successful regeneration, in the last 465 miles, (750km) regardless of the load condition of the DPF diesel particulate filter. Such ìmileage regenerationî is used as an additional safety system to keep the load condition of the diesel particulate filter low.î  


As I say, I was not previously aware of such regeneration programming. Many thanks for the update though Bill. I never cease to be amazed at the great economy that you have managed to obtain with your (now discontinued) Mazda2 and its 1.5 SkyActiv-D engine. Some of it must be down to the engine, but I am sure that some of it is down to your driving skills. 


Best regards,
Doctor D

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