DPF Regeneration

[Deeps]

This is a somewhat lengthy video but explains in depth how DPF regeneration works with mention also being made to Mazda's take on the issue.

https://youtu.be/fNO-oUHmKXU

[Deeps]

Earlier today, with 1,025 km's on the clock,  my CX-5 went through it's second regeneration. With the first taking place at a touch over 500km this appears to bear out my suspicions that Mazda have programmed the firmware to execute a regeneration cycle at the 500 km+/- mark irrespective of the current state of the filter.

This second regeneration was very short in duration and the awful smell that was evident first time around was more acceptable to the nasal passages lol. Whether this was due to my top-up fuel fill being with a so-called better grade of diesel or because the engine had now had a few km's put on the clock I wouldn't like to say.

As an aside - the engine oil level dropped by a couple of millimetres upon checking after the first 500km but remains at the same level with now 1,090km on the clock so oil consumption at this moment in time is negligible. From an appearance aspect, the viscosity appears to be the same i.e. feels like undiluted oil on the fingers,  and the colour is as new with no smell of diesel present.

[Fangface]

Earlier today, with 1,025 km's on the clock,  my CX-5 went through it's second regeneration. With the first taking place at a touch over 500km this appears to bear out my suspicions that Mazda have programmed the firmware to execute a regeneration cycle at the 500 km+/- mark irrespective of the current state of the filter.

This second regeneration was very short in duration and the awful smell that was evident first time around was more acceptable to the nasal passages lol. Whether this was due to my top-up fuel fill being with a so-called better grade of diesel or because the engine had now had a few km's put on the clock I wouldn't like to say.

As an aside - the engine oil level dropped by a couple of millimetres upon checking after the first 500km but remains at the same level with now 1,090km on the clock so oil consumption at this moment in time is negligible. From an appearance aspect, the viscosity appears to be the same i.e. feels like undiluted oil on the fingers,  and the colour is as new with no smell of diesel present.

How are you able to tell the regeneration is happening?  I have done nearly 7000 miles and have not noticed anything out of the ordinary happening during any journey.

[Deeps]

There are a few clues really - (1) if you've set the OBC to read fuel consumption (actual not average) then this will rise for a short period although your speed hasn't increased - assuming you're not accelerating of course. (2) there will be a sort of burning smell a bit similiar to the smell you get with a new heating/toaster element and (3) if you spot any of the last two, then look through the rear view mirror and you might catch a cloud (a puff really) of white smoke - similar but obviously not the same as the black stuff when really giving some throttle to a diesel engine.

[Howard]

Hi, after reading this post maybe I have a concen. My Cx5 diesel averages between 48 to 52 mpg then at regular intervals the average consumption will drop to 42ish, normally when off the throttle going down hill the instant mpg reading is zero, when this event happens its between 20 to 25mpg on the same off throttle down hill conditions. This seems to happen every 200 to 300 miles.
Iv noticed this happing even on really long runs,over 500 mile plus. The car does hardly any runs less than 20 miles ever. Am I being fussy or do you think there is something wrong..
Iv had many diesel cars and iv never had this before.
H

[xtrailman]

Sounds normal to me Howard. Apart from the zero reading down hill i thought mine read 99 mpg off throttle, but rarely use anything but the average read out. CX-5 has a timed regen about 250 miles.

Only once have i seen a cloud of smoke through the rear screen, just as i was pulling into my drive!
My instantaneous readout DROPS when i have a PDF burn. 

[Psythepie]

Why can't we have a DPF regen warning on the display? My car nearly always regens (that I've noticed) when I'm on the way home from work, it seems that the last mile drag uphill provides the ideal throttle/temperature etc conditions for it to happen but the first I notice is when I park up on the drive & the car doesn't go in to iStop mode. My neighbours must think I'm a bit mental because I then have to get out of the car & sniff around it to see if I can smell the tell tale burning smell, if I do I then jump back in the car & drive around for 10 minutes when all I
really want to do is go indoors for a cup of tea! The cars computer knows it's doing it so it can't be that hard for Mazda software bods to write some code to display a message when it starts/stops.

[xtrailman]

Quite agree Howard.

I do know some fiats do have a dash light when a regen is running.
Another thing I've noticed during a regen if I lift off the throttle the exhaust makes a strange noise, sounds a little like an exhaust leak, I've noticed it a couple of times before I twigged it.

[Psythepie]

Also a record of regens completed/failed on the fuel economy monitor screens wouldn't go amiss.

[xtrailman]

Just got back from shopping 3 mile away, DPF was cleaning just as I pulled into the garage, but I couldn't be bothered to waste fuel driving round just to finish it.

Along with a dash indicator, a start DPF burn button would be useful, especially during a long trip.

[Psythepie]

So what are the implications of stopping a regen mid cycle?

[xtrailman]

Diesel in the oil.
Last car raised by around 8mm above full before service. The oil used is designed to cope with some dilution, so I don't worry about it.

[Anchorman]

Car manufacturers don't want the owner knowing that a regen is taking place. It's supposed to be automatic and a lot of owners would worry about it. I'm not keen on leaving mine part way through with the fans running and it smelling of burning or the thought of possible dilution.

It's a legacy of running a modern diesel. 

[Deeps]

A very interesting article posted a little earlier by Willpower that I shall have to read through a few more times. That said, para 3 raised an eyebrow especially as my own CX-5 shall shortly be called into duty pulling our caravan. On a 'typical' motorway run I'm pulling around 2,000rpm at the 120km/h mark with the Auto box of course now in 6th gear. There's absolutely no way these conditions are going to be met when pulling a caravan and I'm now beginning what impact this will have on DPF regeneration.

[xtrailman]

I've had enough of DPF cars.

Yesterday i was driving home from a days fishing a 15 mile trip with 42 mpg on the inaccurate average read out, only to detect the exhaust bubbling noise on the overrun telling me yet another DPF clean was on going.

Read out which shows around 2.5 mpg high was down to 36 mpg, i can get around that with a petrol car, so my next car will probably be a turbo petrol.

Towing i got 25mpg and 27mpg, less the 2.5 mpg error, so really not impressive, i got much more with the manual car