T6 Hovercraft mode - what is actually happening?

[Lightning]

Wife's car was changed from a diesel to a petrol. She hates the smell of petrol. Mainly used for local runs.
Actual cost difference on my modest mileage between petrol & diesel isn't a worrying cost factor.
I'm happy with diesel as the best option for my use with its torque and bhp.

Great!

The torque curve of my 204 petrol is similar the 150 diesel,m, with a wider power band. So there is no issue. The bhp of the 204 petrol is obviously the same as a 204 diesel.

I am just glad we are all happy with our vans.

After spending so much on the van the fuel cost delta is not really an issue.


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[westfalia]

the smell of petrol.

Not that i like the smell but if
i had to use one as an underarm deoderant Petrol would win
against diesel.

 

[2into1]

Trying to get my thread back on track....

My schedule changed so got a proper run in today.

So having had two incomplete attempts to regenerate (my first post), it was interesting to see that 16 mins into today's journey, (5 mins on b roads then all motorway), the regeneration was still running (high idle speed). I wonder how long these regents take, and how that time varies with the nature of the drive underway?

My guess is they take around 20 mins. If that is near accurate, then 'driving around the block' until the regen has finished doesn't seem practical.

Now vwguru has explained that when interrupting a regen, no fuel is being burnt once the engine is stopped. However I guess you then waste all that heat that was built up using extra fuel, and waste that fuel again on your next trip when the temperatures have to be raised again.

Some mechanism to delay (to a point) or initiate a regen (as proposed) does seem logical, although it would bring this complexity front and centre to every driver, including folk who've just hired one for a day, so I can see why it has to stay automated.

I've equally no idea of the chemistry taking place here. Given the amount of extra fuel being burnt, I wonder why they don't just collect the soot and allow us to dispose of it properly (like dog poop), at fuel stations.

 

[deccauk]

When driving, how can you tell when there's a regen? I've never ever noticed anything.

 

[Bellcrew]

When driving, how can you tell when there's a regen? I've never ever noticed anything.

The engine note is coarser/1000 rpm on the tachometer when at idle.

 

[Erbster]

The engine note is courser/1000 rpm on the tachometer when at idle.

Can you tell if, say, you’re on the motorway (ie never at idle)?


caliventures364847572.wordpress.com

 

[Neilos]

Hi all, getting back in to the regen theme. Has anyone experienced a limp home fault due to insufficient fuel and an interrupted regeneration cycle? Slightly worrying if that does happen. Hasn’t happened so far to us but only 2 months in.


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[Loz]

Hi all, getting back in to the regen theme. Has anyone experienced a limp home fault due to insufficient fuel and an interrupted regeneration cycle? Slightly worrying if that does happen. Hasn’t happened so far to us but only 2 months in.


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A member on the T6Forum did this, he thought it would be clever to save fuel by keeping the fuel below 1/4 tank and preventing the regenerations. Eventually, it had to be taken to the dealer on a flatbed!

I have had a limp mode associated with failed regenerations, but it was caused by the build of ash in the DPF caused by a faulty DPF differential pressure sensor.

 

[burnercan]

Eventually, it had to be taken to the dealer on a flatbed

Because the DPF finally blocked since it was unable to regen, or something else?

Edit: To clarify my question, wouldn't the DPF dummy light come on long before the vehicle would need to be towed?

 

[kave]

On the bright side, petrol is cheaper, I’ll never have a DPF light, I won’t run out of AdBlue or over fill it, or have to drive around with more than 1/4 of a tank to avoid a dealer visit, and Euro 4 petrol is still allowed in the London ULEZ, so mine is likely to be useful for longer On top of all this I don’t sound like a hovercraft or get oily hands every time I fill up, which is often...

I wouldn’t swap.


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So instead of oily hands, which can be prevented with gloves, you kill some brain cells every time you fill up? I know what I choose in that case. Since the main climate agenda is reducing co2 I am quite sure the bias against diesel will switch over in it’s favour again. It’s not reasonable to produce 30-40% more co2 which of course the politicians will realize quite soon. Here i Sweden the co2/car/km increased last year, mostly due to newer cars switched from efficient diesel engines to silly petrol/hybrid vehicles.

 

[2into1]

Can you tell if, say, you’re on the motorway (ie never at idle)?


caliventures364847572.wordpress.com

As bellcrew says, you can sometimes detect a coarser engine tone, but higher idle is the easiest way. I’ve got coast mode on, and noticed my higher idle as everyone was slowing to 69.5mph to pass a police car!

Edit: plus if you monitor your fuel consumption you’ll know. 15 mins into the route I took yesterday I’d have expected about 44mpg, but it was showing 34mpg. I think that’s what alerted me to look at the idle speed.

 

[Loz]

Because the DPF finally blocked since it was unable to regen, or something else?

Edit: To clarify my question, wouldn't the DPF dummy light come on long before the vehicle would need to be towed?

Correct, keeping the fuel below a 1/4 of a tank prevented regen, then the light came on so he filled it back up but the continued town driving didn't allow enough time to properly regen and eventually it had to go to the dealer.

 

[Erbster]

As bellcrew says, you can sometimes detect a coarser engine tone, but higher idle is the easiest way. I’ve got coast mode on, and noticed my higher idle as everyone was slowing to 69.5mph to pass a police car!

Edit: plus if you monitor your fuel consumption you’ll know. 15 mins into the route I took yesterday I’d have expected about 44mpg, but it was showing 34mpg. I think that’s what alerted me to look at the idle speed.

Yes, I was watching today and noticed the oil temp climb slightly. When I let off the throttle, the idle speed was higher. Don’t know if temp rise was a coincidence though.


caliventures364847572.wordpress.com

 

[Bellcrew]

Can you tell if, say, you’re on the motorway (ie never at idle)?


caliventures364847572.wordpress.com

When on coast function.

 

[VW Guru]

Because the DPF finally blocked since it was unable to regen, or something else?

Edit: To clarify my question, wouldn't the DPF dummy light come on long before the vehicle would need to be towed?

Hi on T6 models the dpf light will NOT illuminate below a quarter of a tank this is a new strategy and totally different to T5 and 5.1

 

[Volkywagen]

Correct, keeping the fuel below a 1/4 of a tank prevented regen, then the light came on so he filled it back up but the continued town driving didn't allow enough time to properly regen and eventually it had to go to the dealer.

Nice avatar Loz, its a different one every week

 

[M32]

It's a shame there isn't a button or some way of telling the van it's a good time to get its next regen in if its close to needing one.

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There is an app called VAG DPF (only available on Android), This connects to the car via a Bluetooth OBD2 device (I use a Charista dongle) and shows the status of your DPF. On my previous car (T5.1) I used to initiate a regen by driving at >3000 rpm (the engine needs to be warm and not be on empty), the DPF regen would generally start after 10 min and complete after 20min. The app also enabled me to extend my journeys if I was in the middle of an automatic regen and about to arrive home.

The majority of my driving is short journeys and I found the app really useful in helping me understand the DPF regen cycle.

 

[kave]

I just bought the app, took a while to guess which engine group to select so it works. I choose Group 1 CFWA, otherwise no updates. The manuals for this app is not very informative so I have to guess what is happening. I noticed that after a fillup it started regen, drove arround for 20 mins without it finishing. Any info about how long time this can take?

 

[M32]

I just bought the app, took a while to guess which engine group to select so it works. I choose Group 1 CFWA, otherwise no updates. The manuals for this app is not very informative so I have to guess what is happening. I noticed that after a fillup it started regen, drove arround for 20 mins without it finishing. Any info about how long time this can take?

If you look at the VAG DPF interface a red icon appears to indicate a regeneration, once the exhaust temp increases (up to 600deg C) it turns red and the figure on the top right of the screen starts to show negative numbers (this is the amount of soot you are creating in mg’s) The % fill level then starts to reduce. On a long motorway run the bar drops down to about 15%, although sometimes it just stops at about 30% fill. The duration of the regeneration all depends on the level of soot the ECU Has decided is acceptable.
I did read an article somewhere that said the regeneration cycle was semi intelligent and learns from your driving style (i.e lots of short journeys and it will attempt a regeneration at every opportunity, whereas a regular motorway drive van may defer the regeneration until it gets up to high speed - it may be a load of rubbish but it would sort of explain why people’s vehicles all appear to have different regeneration cycles.

 

[colintfcolintf]

We get plenty of threads asking why T6s often imitate a 'hovercraft' when you stop and park up. We know it happens when you stop the engine part way through a DPF regeneration.
But do we know what is actually happening when all those fans are whirring and heat blasting from underneath?
Is it using fuel as I wander off with the keys in my pocket?
Is it just using 12v to power the fans to cool down the process that was already underway?
- am I doing 'harm / wear' each time it happens?

I'm particularly annoyed that the 2(?) hourly forced regeneration always seems to having terrible timing. Today it again chose to start a regen just as I returned from a long run. It did its hovercraft impression as I nipped into Tesco before arriving home. It did it again as I arrived home. It will do it again tomorrow when I drive 4 miles to yoga, and probably again as I return.
I'll then be back to longer drives, free from re gens as it waits until I'm a mile away from home to start the next one.
I read that some users leave the engine running to allow it to finish the cycle, or drive a few extra miles to achieve the same - which rather negates the environmental goals of the system.
I think the more we know about the process, the better we can 'manage' it.
- so what is happening?
- how long does it take?
- does that timing depend on how its being driven?
- how long is it between regens?
- is that fixed or does better trips lengthen the intervals?

This happened to me for the first time after refuelling today - I was somewhat concerned! Thanks for the info. It’s due a good run next start up, so hopefully all is ok

 

[sidepod]

You’d have thought by now these generic forum software packages would include a Thread Resurrection Alert when posting?

 

[Califan61]

@vwguru can you advice?

1. If you drive for 30-45 minutes, mainly 60mph dual carriageway but with roundabouts every 5-10 mins will the regen continue when not at higher driving revs?

2. I assume it's best to try to complete a regen but if you have to stop (for fuel) will the system reset to start the cycle again or continue from where it had got to (and continue until completed)?

Thanks

 

[larrylamb]

@vwguru can you advice?

1. If you drive for 30-45 minutes, mainly 60mph dual carriageway but with roundabouts every 5-10 mins will the regen continue when not at higher driving revs?

2. I assume it's best to try to complete a regen but if you have to stop (for fuel) will the system reset to start the cycle again or continue from where it had got to (and continue until completed)?

Thanks

vwguru has left the forum unfortunately.

 

[WelshGas]

@vwguru can you advice?

1. If you drive for 30-45 minutes, mainly 60mph dual carriageway but with roundabouts every 5-10 mins will the regen continue when not at higher driving revs?

2. I assume it's best to try to complete a regen but if you have to stop (for fuel) will the system reset to start the cycle again or continue from where it had got to (and continue until completed)?

Thanks

Q1. Yes , it should complete as long as you are driving.

Q2. No. It the cycle fails to complete it will start over.

If you use the Carista OBD reader you can monitor the DPF and initiate a cycle if the conditions are met.

 

[Perfectos]

@vwguru can you advice?

1. If you drive for 30-45 minutes, mainly 60mph dual carriageway but with roundabouts every 5-10 mins will the regen continue when not at higher driving revs?

2. I assume it's best to try to complete a regen but if you have to stop (for fuel) will the system reset to start the cycle again or continue from where it had got to (and continue until completed)?

Thanks

The regen is a measurement taken at two points on the DPF , one front sensor , one rear sensor , these calculate the % soot levels And initiate the regen when soot levels increase above a pre determine amount. (Driving style ).
During Regen the soot is incinerated by fuel being deliberately delivered into the Exhaust, which ignites in the DPF chamber Burning off the Soot which exits via the exhaust.
if a regen is stopped by turning the engine off , it will restart during the next ignition on , providing the parameter criteria is met.