DPF Regeneration

[raisbeck]

I have a Greenline with a DPF filter (Boo hiss) Fear not this isnt yet another DPF rant

I havent had any problems with it. Many have and many havent but thats not the point of this posting.

My question is that occasionally, maybe once every couple of days the engine sounds a lot more 'agricultural' as it gets to around 2000 rpm. You really notice it and I can only compare it sounding more diesely....sort of sounds like a a low bass drone. It can vanish in almost an instant and you are back to the nice quiet....ish normal engine note.

It only ever lasts for about 5 minutes tops. I wondered if this was some kind of regeneration cycle with the engine somehow adding fuel later to heat up the DPF and this is what I am hearing. That or the EGR is totally closed to heat up the combustion for the same result.

Are there any technical experts out there on PD engines fitted to the Greenline ? I even read somewhere that the injector camshaft has an extra lobe for post injection but not so sure myself. This post injection is added by the ECU solenoids on the injectors themselves.

I dont think my filter gets blocked much. Pretty much extended fast runs every day.

I had thought the DPF on the Greenline was totally passive and relied on driving style.......

Love the car so far, just curious on its inner workings....

[FabiaGreenline]

I have a Greenline with a DPF filter (Boo hiss) Fear not this isnt yet another DPF rant

I havent had any problems with it. Many have and many havent but thats not the point of this posting.

My question is that occasionally, maybe once every couple of days the engine sounds a lot more 'agricultural' as it gets to around 2000 rpm. You really notice it and I can only compare it sounding more diesely....sort of sounds like a a low bass drone. It can vanish in almost an instant and you are back to the nice quiet....ish normal engine note.

It only ever lasts for about 5 minutes tops. I wondered if this was some kind of regeneration cycle with the engine somehow adding fuel later to heat up the DPF and this is what I am hearing. That or the EGR is totally closed to heat up the combustion for the same result.

Are there any technical experts out there on PD engines fitted to the Greenline ? I even read somewhere that the injector camshaft has an extra lobe for post injection but not so sure myself. This post injection is added by the ECU solenoids on the injectors themselves.

I dont think my filter gets blocked much. Pretty much extended fast runs every day.

I had thought the DPF on the Greenline was totally passive and relied on driving style.......

Love the car so far, just curious on its inner workings....

The Greenline 'drone' has been mentioned in threads before, it seems to come and go but seems like we all experience it, as to what it is who can say at this point. Hopefully somebody can shed some light on it.

[mrgf]

Think its just "normal diesel noises just less insulated on the lightened Greenline...

As you mentioned, goes away after a few mins. may be either when cold or even when overworked a little... Engine management compensating for something.. (Doing its job)

[Fabia00]

Still sounds like the DPF to me especially as it goes away and doesn't appear to have much of a pattern, the greenline is the only pre-facelift fabia/ roomster with a DPF. It probabaly burns extra fuel to heat up the DPF and clear it.

[raisbeck]

Still sounds like the DPF to me especially as it goes away and doesn't appear to have much of a pattern, the greenline is the only pre-facelift fabia/ roomster with a DPF. It probabaly burns extra fuel to heat up the DPF and clear it.

I think your probably right. It sounds more like exhaust note than an induction noise. It also goes away instantly when you let off the pedal. So its not induction air I reckon. Hard to see how they actually do the fuelling thing as its timed on a cam which cant change. Maybe the solenoids let more fuel in than normal but cycle it along the cylinders so you dont get surges or stutter in the drive.

Bit odd as it came in on me while driving at speed well over 2000 rpm where I had been for over 15 mins. It suggests that normal driving wont keep the DPF clear and it need the extra push now and again. That said it could be a timed thing and is automatic and not sensed.

Of course I could be talking utter nonsense and its none of these. Always lasts for about 5 mins...........I must ask a mechanic.

[RedDog]

The brochure says " A driving style is required during regeneration, where a constant vehicle speed above 37 mph must be maintained. " It doesn't say how long it needs to be maintained. I had driven diesels for the last 14 years but since these DPFs have been used I decided to go back to petrol. My yearly mileage isn't enough to keep these filters clear. :no:

[raisbeck]

The brochure says " A driving style is required during regeneration, where a constant vehicle speed above 37 mph must be maintained. " It doesn't say how long it needs to be maintained. I had driven diesels for the last 14 years but since these DPFs have been used I decided to go back to petrol. My yearly mileage isn't enough to keep these filters clear. :no:

I do huge mileage each year, all of it long runs so its not a problem. My main query was whether it is entirely down to driving style that keeps the DPF clear or whether there is some kind of active adjustment to the way the fueling works to periodically assist a regen. The occasional drone these cars get at around the 2000 rpm mark for 5 mins might be this regen. I thought it was always passive on Fabia Greenlines and only the common rails that directly adjusted fuelling for clearing the DPF.

This wasnt meant to be a DPF thread, more a " whats that noise thread"

MY MPG is getting better every day as the engine runs in and gets looser. NO sign of the dreaded DPF light (touch wood).

[RedDog]

Are there any technical experts out there on ........

I should have read your post more carefully! I'm the furthest thing there can possibly be to a technical expert!!

Hope you get your problem sorted!

[mrgf]

The brochure says " A driving style is required during regeneration, where a constant vehicle speed above 37 mph must be maintained. " It doesn't say how long it needs to be maintained.

I think I remember reading that you need to drive at the "Higher" speed for around 15 mins. This should be easily obtainable for most drivers who chose, on purpose, to buy a diesel, which is after all, intended to be a mile munching fuel sipper, rather than a short distance gas guzzler!!!

BTW, the higher speed should also be done in either 4th or 5th gear. this suggests that engine speed, is not the point but rather the heat build up needed to burn off the soot, so using MORE fuel, would be counter-productive!!

[mrgf]

The brochure says " A driving style is required during regeneration, where a constant vehicle speed above 37 mph must be maintained. " It doesn't say how long it needs to be maintained.

I think I remember reading that you need to drive at the "Higher" speed for around 15 mins. This should be easily obtainable for most drivers who chose, on purpose, to buy a diesel, which is after all, intended to be a mile munching fuel sipper, rather than a short distance gas guzzler!!!

BTW, the higher speed should also be done in either 4th or 5th gear. this suggests that engine speed, is not the point but rather the heat build up needed to burn off the soot, so using MORE fuel, would be counter-productive!!

[raisbeck]

Yes, I think the theory is that when you are at speed the engine is working harder than it would at slow speed with higher rpm. I wondered if this 'drone' noise was the car adding more fuel to raise the exhaust temperature, I just cant see how it can do this as the injection timing is fixed by the injection camshaft unlike the CR engines. It certainly sounds like exhaust noise. Also the exhaust on these cars exits at the rear of the engine close to the firewall so you are bound to hear it more. I worked out that mine does this noisier note at around 2000 rpm about once every three days for about 5 minutes. Thats about once every 300 miles. It is very noticeable and specific when the noise stops. Odd.....

It will be interesting to see how the new CR DPF engines reliability/efficiency stacks up. I have seen mixed reviews. The fuel efficiency apparently isnt quite up to what is advertised and my local dealer was very concerned about the DPF due to so many cars being sold to taxi drivers....Octavias mainly.

I will perhaps have to resign my occasional noisy engine 5 mins to the drawer labeled "It just does that sometimes".

I

Edited 31 May, 2010 by raisbeck

[raisbeck]

I think I managed to answer my own posting. After much searching on the net and visiting other foreign VAG forum sites (of course not a patch on Briskoda.......no loyalty issues here)

I repeatedly see mention of PD engined diesels fitted with a DPF having a modified camshaft for the unit injectors. This allows post fuel injection. This is ECU controlled by the solenoid valves remaining closed for longer therefore putting more fuel in later. Normally they open to dump the remaining fuel in normal operation.This explains the noisier drone of exhaust note. Its a form of active regeneration. This is in addition to the normal regen that occurs when the car is driven normally on longer runs etc. It apparently only kicks in when needed and operates above 1800 rpm. This would also explain short journeys clogging the filter as you never properly reach or maintain regen temp/rpm.

Be interesting to see if anyone who has had the DPF light illuminate has also noticed this 'noisier' engine note during the run to put the light out.

I found some technical info regarding the design of DPF fitted to Fabias

http://new.skoda-auto.com/Documents/EnvironmentTechDev/EnvironmentTechDevDPF.pdf

It states that although mainly passive in operation it modifies the combustion process every 1000k to clear the DPF. I know Fabia isnt actually listed but going by the date and engines used I would assume they are the same setup

I would therefore declare this 'noise' to be normal................I think

Edited 31 May, 2010 by raisbeck

[raisbeck]

I was in the dealers today ordering the cruise control upgrade. I took the opportunity to ask about the DPF regen process on my Greenline.

A very helpful mechanic spoke to me who also happens to own one. The DPF is actively monitored by the ECU and when the DPF gets restricted to a certain point (this is waaaaaay before its getting blocked to any degree) it initiates a regen. This regen is carried out by injecting fuel after it would normally have stopped the injection cycle. The Greenline can do this as it has modified cams for post injection which is permitted by the injection solenoids not dumping the remaining fuel after normal running injection.

It is this regen that is the noise we Greenline drivers hear from time to time. The sound is the extra fuel combusting in the exhaust to heat up the DPF. The length of time it does this for depends on how restricted the DPF is and the way you drive while its regenerating. Mine does it for 5 to 10 minutes every 2 or 3 days when I am on the dual carriageway. Sometimes its when I am on slower roads and does take longer.

The DPF cannot keep itself clear by itself. It has to do this regen due to the high temps required and is completely normal. I noticed no noticeable increase in fuel consumption when it does this regen so it cant take a lot of fuel to do it above what's normal.

He also explained the forced regen process. Its pretty scary. They start it using the VAG diagnostics and leave the car outside while it revs itself in neutral. The DPF gets SERIOUSLY hot and they do it outside as when they tried it inside the heat off the DPF burnt the floor !! He likes to keep extinguishers handy as well just in case. This is the same for ALL cars they get not just Fabias.

They don't really get Greenlines having DPF problems apart from the odd one which has a manufacturing fault usually very early on with low mileage. Otherwise its mostly folks who should never have bought or been sold a car with a DPF due to how they use it. They don't see hardly any Skodas with blocked filters.......a few renaults.....

That wraps that up....I guess

[Guest]

At around £1,500 for a filter replacement that's good news. Incidentally, all the TDI PD engines have post fuelling injection for cleaner hotter burning of exhaust gases, and operated by a secondary camshaft lobe to give that extra little pump. Actual injection timing is controlled by ECU and can be remapped anytime, but not recommended for the Greenline in case you mess up stuff. As you say the Greenline has that special additional programed feature of raising it's exhaust gas temp when needed. Well done on the research. Very helpful.

Edited 12 June, 2010 by Estate Man

[FabiaGreenline]

All makes interesting reading. On Friday I drove up to East London from Bournemouth normal motorway route and not hanging around, after 2.5 hours of quick motoring then a 30 min run at 50 then down to 30. When I pulled up and reversed in to my space, my DPF light came on which surprised me considering the journey the car had just done. This only the 4th time since October and I'm wondering if the ECU is giving the warning on set intervals.

[raisbeck]

All makes interesting reading. On Friday I drove up to East London from Bournemouth normal motorway route and not hanging around, after 2.5 hours of quick motoring then a 30 min run at 50 then down to 30. When I pulled up and reversed in to my space, my DPF light came on which surprised me considering the journey the car had just done. This only the 4th time since October and I'm wondering if the ECU is giving the warning on set intervals.

I would get the car checked out. Doesnt seem right as the warning light is only on to show excessive blockage which needs a proper run to clean it out. From your description you werent pootling about. Might have a dodgy sensor or maybe something else causing excessive soot production.

Mine has completed 4500 miles now and I have never seen the light ...touch wood (except on start to show its working)

[raisbeck]

At around £1,500 for a filter replacement that's good news. Incidentally, all the TDI PD engines have post fuelling injection for cleaner hotter burning of exhaust gases, and operated by a secondary camshaft lobe to give that extra little pump. Actual injection timing is controlled by ECU and can be remapped anytime, but not recommended for the Greenline in case you mess up stuff. As you say the Greenline has that special additional programed feature of raising it's exhaust gas temp when needed. Well done on the research. Very helpful.

I read the engineering description of how the unit injectors work on the PD engine. The cam is shaped to give a rapid increase in injection pressure followed by a steady injection phase, this gives the louder knocking you get same as a traditional diesel. PD engines still knock compared to the CR engines due to the minimal control of the combustion propagation. CR engines can inject up to 5 times per cycle to give that quiet engine note. That said the mechanics say the PD is a better engine due to the higher injection pressure of the unit injectors over the CR method. Gives more torque and is very efficient albeit rattly.

The Greenline cam is shaped to extend the period that it can inject fuel. The other affect of this is that the Greenline produces maximum torque at a lower rev range.

Edited 12 June, 2010 by raisbeck

[Guest]

Currently, I'm waiting to see how well the CR fuel pumps last on the new engines. Certainly cr gives added flexibility to provide infinite injection capabilities, but at the pressures they operate at it is unlikely they will have anywhere near the longevity of the PD engines unitary injection system which has proven bullet proof and very nearly as good as the latest cr engines in terms of performance and economy, and even cleanliness of burn (but leaving aside the noise factor). Although I haven't read the spec for the new engine pumps, I believe they rely on diesel fuel for pump lubrication as do most others. This is currently a weak spot on mostly all cr engines with expensive pump failure still happening much too often.

[FabiaGreenline]

I would get the car checked out. Doesnt seem right as the warning light is only on to show excessive blockage which needs a proper run to clean it out. From your description you werent pootling about. Might have a dodgy sensor or maybe something else causing excessive soot production.

Mine has completed 4500 miles now and I have never seen the light ...touch wood (except on start to show its working)

When I left London on Monday night, started the car after sitting there since Friday and no DPF light. About 4 miles down the road on it came again, I couldn't take my normal route through the Blackwall Tunnel as it was closed so I had to stop start across London East to West then out to the M3. Soon as I increased speed after the lifting of the 50 limit the light went out straight away. I also just experimenting, the car wouldn't rev beyond 3000 rpm in neutral with the DPF light on, but would take off in 1st and up the gear no issue to the red line. Still it got a good stoke up on the way home, and again I've noticed an increase in performance after this DPF with the (ahem) top speed. I don't think there is anything wrong with the car or DPF I'm just not convinced it based entirely on driving style.

[raisbeck]

When I left London on Monday night, started the car after sitting there since Friday and no DPF light. About 4 miles down the road on it came again, I couldn't take my normal route through the Blackwall Tunnel as it was closed so I had to stop start across London East to West then out to the M3. Soon as I increased speed after the lifting of the 50 limit the light went out straight away. I also just experimenting, the car wouldn't rev beyond 3000 rpm in neutral with the DPF light on, but would take off in 1st and up the gear no issue to the red line. Still it got a good stoke up on the way home, and again I've noticed an increase in performance after this DPF with the (ahem) top speed. I don't think there is anything wrong with the car or DPF I'm just not convinced it based entirely on driving style.

There is a wealth of opinion and conjecture on other forums regarding the DPF in VAG vehicles. Its a case of take your pic. My driving is nearly all dual carriageway with tiddly town sections which may explain why I have been ok. its comforting to think the DPF light coming on is more of a reminder than an issue.

Mine did a regen on Monday as I left work and I got my best mpg so far, thats staying at near 70 all the way. 74 mpg. Total average on the computer thingy (never reset since I bought it) is 71. Just before it does its regen thing I get around 68-70.

Did you notice the engine note was louder during the entire period the DPF light was on ?

[Guest]

That's brilliant miles per gallon man!! That's prolly going to be the cheapest car to run you've ever had.

[FabiaGreenline]

There is a wealth of opinion and conjecture on other forums regarding the DPF in VAG vehicles. Its a case of take your pic. My driving is nearly all dual carriageway with tiddly town sections which may explain why I have been ok. its comforting to think the DPF light coming on is more of a reminder than an issue.

Mine did a regen on Monday as I left work and I got my best mpg so far, thats staying at near 70 all the way. 74 mpg. Total average on the computer thingy (never reset since I bought it) is 71. Just before it does its regen thing I get around 68-70.

Did you notice the engine note was louder during the entire period the DPF light was on ?

No there was not 'drone' of the regeneration for the period of the DPF light except for the short time after the car was warmed up which lasted about 2 minutes. I was really stonking it back home and it returned 53mpg with city and its stonk for over 80 miles. I'll be interested to see how well it goes out on the german autobahn in September, a far cry from the 94mpg a couple months ago!! One thing I noticed when I parked and got out the hot tingling sound from the exhaust cooling off is absent which I've had on all my other cars except my classic 504 diesel which is a slow old magic carpet anyway, suggesting it really doesn't get that hot in the exhaust by itself, hence the need to regen.