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Diesel Particulate Filter - Questions

DannyScotland

Passed Driver's Ed
Location
UK
All,

I’m a newbie when it comes to a) Golf’s and b) this forum so as previous newbies have said, please go easy on me.

I am the proud owner of a Golf mk7 GT estate, diesel. It’s a brilliant car and I really enjoy driving it however earlier DPF horror stories have worried me somewhat. Hence, my question is around the DPF, I have done numerous searches but still somewhat puzzled by this technology. I understand the concept of the unit and the methods of clearing via active and passive regeneration but still have a few questions perhaps someone may be able to help me with.

I did two long (ish) journeys on Sunday and Wednesday evening – ones which I felt would qualify for passive regeneration to occur. The car didn’t move Thursday and yet this morning when I parked up at work the fan was on and the revs were up as if an active regeneration was occurring.

So I guess my questions are (sorry there are a few):

  1. Do active regenerations take place regardless of the condition of the DPF soot loading?
  2. Do active regenerations take into account passive ones or is active just time / mileage based?
  3. I take it high revs and fan running continuously is a sign of a active regeneration taking place?
  4. When an active regeneration has been interrupted (such as this morning) is it advisable to take the car for a long drive to start the regeneration (passive or active) and clear out the dpf?
  5. Suppose an active regeneration occurs and takes the soot loading to say 20% when interrupted. When conditions are right will the regeneration start again to take the loading to 0% or wait until it builds back to 45%?
  6. As per the handbook, best way to start the passive regeneration is 4th gear at a speed of 50mph or more?

I have read that some people expect a regeneration every tank or so, and I have also read some people get them more often.

Appreciate your help in helping me understand this…

DannyScotland
 

pango1in

Passed Driver's Ed
Location
Nottingham
My own testing...

I spent a while testing this out when I got my golf. This testing included logging all active regens, as they were spotted and hooking up the car to a Vagcom unit and driving around for a morning, measuring the dpf input and output temps etc.. My detailed results have been posted on another forum.

Everything has been confirmed with two VW master technicians.

Firstly, the golf 7 does not passively regen. The exhaust doesn't even reach the magic 350C under normal driving. The way that the car deals with soot is to collect it in the dpf and then to actively burn it off when the dpf is 45% full. This happens for me at about 200-300 miles. The car then artificially heats the exhaust up to 600C which gets the soot volume down pretty quickly. About 10 minutes.

The method of heating is to squirt fuel into the cylinder on the exhaust stroke, so that it will combust in the exhaust, rather then the cylinder. It drinks more fuel, the golfs ecu raises idling rpm and the fan keeps running if you interrupt the cycle by shutting off the engine.

The manual says drive it around for 15 or so minutes so that you can allow a regen enough time to fully take place. Speed of travel, or driving rpm doesn't seem to have any effect. I've had the car stationary for most of a regen and this hasn't caused it to take any longer, and the exhaust temp doesn't drop.

If you interrupt the regen, sometimes it comes back on the next time you start, sometimes it doesn't. I assume that it finishes it off sometimes, and others it doesn't.
 

DannyScotland

Passed Driver's Ed
Location
UK
Many thanks for your post - you've obviously done quite a bit of research and I for one found it very useful.

From my limited experience of the car what you are saying does make sense and I have to admit I never appreciated the fact that passive regen's have practically zero change of occurring. Fair enough - just leave it for active regens to do their job...

Thanks
 

RPS99SHO

Ready to race!
Location
Frederick, MD
I think "high-flow downpipe" means DPF-less downpipe. I highly doubt you're going to find a high-flow DPF. There were I believe 3 DPF-less options for the mk6 (I know because I bought one). I wouldn't be surprised if a few started popping up for the mk7 shortly.
 

Korab

Ready to race!
Location
United States
I think "high-flow downpipe" means DPF-less downpipe. I highly doubt you're going to find a high-flow DPF. There were I believe 3 DPF-less options for the mk6 (I know because I bought one). I wouldn't be surprised if a few started popping up for the mk7 shortly.

so what do they do - code out the whole dpf sensor, regen system? How does that affect the adblue system?
 

RPS99SHO

Ready to race!
Location
Frederick, MD
Not sure how that affects adblue but I'm guessing the whole system is just removed. The regens can be tuned out. (I had a mk6 TDI, I don't have hands-on knowledge of the mk7-specific TDI systems)
 

pedg

New member
Location
Yorkshire
This will be an mot failure here in the UK now.

A car only needs to have a visible DPF for the MOT. It doesn't need to have anything inside it, just be visible. I.e If it has been gutted and mapped out, the car will still pass! As long as the MOT tester can see it's there!
 

ColinStone

Ready to race!
Location
United Kingdom
Car(s)
MKVII 2016 Match BM
A car only needs to have a visible DPF for the MOT. It doesn't need to have anything inside it, just be visible. I.e If it has been gutted and mapped out, the car will still pass! As long as the MOT tester can see it's there!

Don't think that is strictly true. Car has to have original kit. If tester suspects that DPF has had core removed, then it will be a fail.

And if core has been removed, the owner is a self serving cretin.
 

pipsyp

Ready to race!
Location
Sussex
These things have come a long way from the very early TDI PD implementations which tended to go horribly wrong if not driven in a certain way. This is because PD injection was never designed with DPF tech in mind and was thrown together. That said I had a Mk5 Golf Blue motion and it never gave me any trouble.

The latest generation cars can be driven pretty much however you like with little or no problems. The car will attempt to regeneration every few hundred miles...if it gets disrupted it just kicks off again next time the car is driven and it's warmed up.

The car also tries to raise the exhaust temp periodically so that some of the soot gets burnt off naturally and the regeneration cycles have less to do. I've never seen any of my DPF equipped VAG cars (and I've now had several) perform a forced regeneration (with the telltale on the dash).

You are more likely to experience sensor faults than an actual fault with the DPF...sensor faults are just one of those things and cheaply/easily resolved.

DPF's are of course wear and tear parts and have an estimated 100k mile life expectancy...but most cars will do many more miles before problems with the actual DPF becoming blocked will occur.

Replacements aren't cheap but equally they are not as pricey as they once were and can be done at regular garages/specialists now and are not just a main dealer job as they once were.

I simply just would not worry.
 
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