DPF figures

[snowathlete]

Looked with scanner today and this is what I got:

 

time since last regen: 27744 S(econds presumably)

oil ash volume: 0.1 L

soot mass calculated: 0.048 lb

soot mass measured: 0

KM since last regen: 156850 M(eters, actually not KM)

Fuel consumption since last regen: 13.2L

oil ash volume: 0.082 lb

oil ash limit: 0.155 lb

 

Question: what's the deal with the limit? Is that the limit till a regen or limit till the DPF needs replacing?

If it's the later than I'm a little surprised to be over half way there after just 42k miles.

[DEL80Y]

A  lot of good reviews from the VAG DPF app from google play..

[chimaera]

A small amount of engine oil gets burned alongside the fuel due to blowby in the turbo seals, plus the routing of the crankcase vent back to the intake. A certain portion of the oil is uncombustible and leaves the cylinder as ash which then gets lodged in the DPF alongside diesel soot. The ash cannot be burned off during a regen so it stays in the DPF. Over time the ash volume builds up in the DPF: the limit value is the total amount of ash the DPF can store before it must be replaced.

 

Using incorrect oil can result in hitting this limit much earlier than normal. Lots of short trips on a cold engine can speed up the process too.

[owilliams1]

I'm on 126k miles, I'll check mine tomorrow with the DPF app, and post the results. 

[snowathlete]

1 hour ago, chimaera said:

A small amount of engine oil gets burned alongside the fuel due to blowby in the turbo seals, plus the routing of the crankcase vent back to the intake. A certain portion of the oil is uncombustible and leaves the cylinder as ash which then gets lodged in the DPF alongside diesel soot. The ash cannot be burned off during a regen so it stays in the DPF. Over time the ash volume builds up in the DPF: the limit value is the total amount of ash the DPF can store before it must be replaced.

 

Using incorrect oil can result in hitting this limit much earlier than normal. Lots of short trips on a cold engine can speed up the process too.

 

I don't know what kind of driving the car has had before as we've only just bought it but it will get more short journeys than long ones under our ownership. It had Skoda servicing except last year's service, don't know what oil they used that time. We're going to give it an oil change with VW oil in the next couple of weeks. Anything else we can do to reduce the build up?

[snowathlete]

1 hour ago, DEL80Y said:

A  lot of good reviews from the VAG DPF app from google play..

 

someone not too far away offered to take a look for me as we don't have an Android phone, but I expect I might need to keep an eye on this so perhaps it makes sense to buy a cheap second hand Android phone just for this.

[chimaera]

Make sure the oil change is done with oil that meets VW spec 507 00 as these have to be low ash oils.

[silver1011]

Repeated short journey's will shorten the life of the DPF.

 

A DPF likes to be hot to allow for passive (rather than active) regeneration.

 

Not to say the DPF will fail prematurely, just that it won't last as long as it would it doing regular longer journeys.

[owilliams1]

18 hours ago, owilliams1 said:

I'm on 126k miles, I'll check mine tomorrow with the DPF app, and post the results. 

Went to use my OBD adapter, and the dog has chewed it. So new one is in the post, once I get some time I'll post the results. Just wanted to update.

[snowathlete]

I got the app, installed on an android tablet we have, and using a bluetooth vgate icar 2 adapter.

It seems very good, my only complaint is that it does not display "oil ash (g)" for my engine (CFGB) which seems to be one of the most pertinent pieces of data. This surprised me because I looked on the foxwell scanner I borrowed and the information is available in the ECU. I've emailed the app developer to ask if it can be added.

[snowathlete]

I noticed today that my "soot mass measured (g)" is a negative, -0.02.

Surely it shouldn't be a negative figure? I'm close to a regen so will check after that to see what changes.

[xman]

2 minutes ago, snowathlete said:

I noticed today that my "soot mass measured (g)" is a negative, -0.02.

Surely it shouldn't be a negative figure? I'm close to a regen so will check after that to see what changes.

 

 You should email the app developer about that too. 

[snowathlete]

that was my thought too but I checked with a scanner and it's the same on there as well. 

[chimaera]

It's estimating soot mass based on pressure drop across the filter. If it's just finished a regen and soot loading is close to or equal to zero, -0.02g is well within the uncertainty limits for the estimation procedure.

[snowathlete]

15 minutes ago, chimaera said:

It's estimating soot mass based on pressure drop across the filter. If it's just finished a regen and soot loading is close to or equal to zero, -0.02g is well within the uncertainty limits for the estimation procedure.

 

thanks, it hasn't just finished a regen though, it's about to have one, almost certainly tomorrow. I'll report back what happens.

[snowathlete]

So we did a regen today, with the app connected. Got down to 24% left and then it cut off because the fuel tank reached the reserve level. I was aware it would not start a regen if fuel was low but had hoped it would continue had it already started. Unfortunately not. Anyway, lesson learnt, and means I'll have another regen sooner but at least I burnt some of it off. Was at something like 22g and went down to 5.45g.

 

Soot Mass Measured (g) is now at -5.09 so it does seem this minus figure is not right. Could it be that one of the sensors is faulty or incorrectly calibrated? And could the emissions fix have caused this problem and be fixable under the 24m guarantee? I can ask the dealer but it would be good to understand it myself first.

 

DPF gas temps reached about 550C in regen, which I assume is normal?

 

What does the High Pressure EGR closing % indicate? It was at 100 in regen and in the 60s when I checked after regen.

 

What do the Post injection 1/2/3 (mg/str) measures indicate?

 

[xman]

2 hours ago, snowathlete said:

 

DPF gas temps reached about 550C in regen, which I assume is normal?

 

 

550C! And if that doesn't produce NOx by the bucket load, then I'm a (vw test) monkeys uncle  No wonder those monkeys started coughing.

 

Post injection is what happens when an active regen is required, to increase DPF temperature.

 

EGR 100% probably means egr is closed and 100% exhaust going straight out during regen, again to keep temperatures high. 

 

Just guessing but maybe the negative figure is a measure of how much soot it will take to the next regen. I.e. it wont regen until another 5.09g is stored.

[chimaera]

A negative soot loading after a regen sounds like there's something not quite right here. Given that it's calculated from the pressure drop across the DPF it could be that one of the sensors is giving spurious readings. It's unlikely to be due to the update but it's no harm asking for it to be covered. I think a trip either to someone with VCDS or to a dealer for further diagnosis is needed.

 

DPF temperature is not the same as exhaust temperature. Remember that during a regen, the accumulated soot is being burned off so of course it's going to get hot.

 

100 % EGR closing means the engine is not using EGR at all, again normal during a regen to provide extra oxygen to help the soot burn off. Any NOx produced by the engine during regeneration is also going to be consumed to oxidise the soot.

 

Post injection is how the DPF lights off: some extra fuel is injected late in the combustion cycle to be carried through to the DPF to help the regen along.

[snowathlete]

I couldn't believe the monkey/human exhaust experiment stuff, astonishingly bad.

 

Thanks xman for explaining those measures.

[snowathlete]

20 minutes ago, chimaera said:

A negative soot loading after a regen sounds like there's something not quite right here. Given that it's calculated from the pressure drop across the DPF it could be that one of the sensors is giving spurious readings. It's unlikely to be due to the update but it's no harm asking for it to be covered. I think a trip either to someone with VCDS or to a dealer for further diagnosis is needed.

 

DPF temperature is not the same as exhaust temperature. Remember that during a regen, the accumulated soot is being burned off so of course it's going to get hot.

 

100 % EGR closing means the engine is not using EGR at all, again normal during a regen to provide extra oxygen to help the soot burn off. Any NOx produced by the engine during regeneration is also going to be consumed to oxidise the soot.

 

Post injection is how the DPF lights off: some extra fuel is injected late in the combustion cycle to be carried through to the DPF to help the regen along.

Thanks for your help. No faults come up on a Foxwell scanner, I know it's not as good as VCDS but it seems to be pretty good with fault codes. But dealer might know what else to look for. I found post about an Audi which suggests I might have a damaged hose or a sensor problem:

https://www.cartechnology.co.uk/printthread.php?tid=7168 but as it talks about incorrect resetting after regen and as the regen on mine was not completed that could plausibly be why it didn't reset properly, so I will wait until there is another regen first and do my best to complete it and then see if the value resets properly. If not then I'll talk to the dealer about it.

 

Do the figures for the 3 post injection measures tell us anything of interest that should be looked out for beyond the figures being >0 therefore it's doing a regen?

Edited 1 February, 2018 by snowathlete