DPF regen - hot turbo

[patrickhorton]

170TDi - Noticed that DPF auto regen seems to continue even when the car is idling if the regen cycle is not complete. If you lift the bonnet during a regen the amount of heat around the turbo is tremendous.

I reckon it must be bad news for the turbo if you switch-off mid regen cycle. Everyone always goes on about cooling the turbo after a fast run - this is impossible with the regen on.


Yesterday I could tell a regen was underway when I got home. Left the car idling for 10min and regen continued - still loads of heat. Plugged in VCDS to confirm and took the car out again till it finished (20min and 15miles later). Turbo outlet temp 800degC for whole time then dropped back to normal when finished.
It seems crazy to switch off and cut the turbo's oil supply when it is 800C. It's also pretty crazy to go driving around til a regen finishes...

Can anyone explain that it's ok to just switch off?

[Adman]

I have the same engine. How do know when the regen is underway?

I just try and take it easy when i know i will be switching the car off

Ad

[randall977]

Ditto - do you need a VCDS? I've never noticed any excessive temperatures under the bonnet...

[patrickhorton]

I have the same engine. How do know when the regen is underway?

I just try and take it easy when i know i will be switching the car off

Ad

I notice a slight roaring noise with the window down as I gently accelerate in low gear through 1200-1500revs. Most of my journeys are 12miles/30min. As the regen only starts with a warm engine and then takes 20min or so, it almost always will still be doing it at the end of my journey. When I switch off and get out of the car everything sounds hot - exhaust tinking as it cools. Also the tail pipe may be very hot to touch; noticeably hotter than after a normal run. Drive characteristics are also a bit different slightly less willing overtaking and slightly less smooth light load acceleration.

Using VCDS, measurement blocks 75 show turbo outlet and DPF outlet temperatures and a % figure for how blocked DPF is. During regen, the turbo outlet is held very steady at 800degC. If the revs are low, or the engine is slowing (accelerator backed off & so no fuel input) the temperature drops sharply - presumably regen is paused. With no regen (normal running) turbo outlet temp generally varies between 300 and 600 depending on load. The % blocked figure falls slowly to around 10% during the regen.

Patrick

[patrickhorton]

Proved that DPF is definitely end of life. This is shown by a value for ash content of the filter read from VCDS/VAGCOM.

With nothing to loose, I've taken a look inside the DPF and done a few modifications...

Watch this space if anyone wants to know if my cunning plan has a happy ending.... Now where did I put those lucky socks?

P.S.
Thread started in VCDS section for advice of setting values in ECU for new DPF.

[a8 tech]

lol

[patrickhorton]

The method in my madness was to open up the DPF and grind the end off the matrix to open up the clean outlet channels. The ash in the incoming channels was clearly visible after this - like red fine red sand and impossible to flush out. The idea is that by leaving the matrix in place, the back pressure and temperature differentials of the DPF show look similar to a new one and fool the ECU. The last thing is that the matrix should still function like a cat to burn off hydrocarbons - I don't really want a smelly exhaust. Soot will no longer be filtered but some will stick to the dpf walls which should burn off on the short, timed regen which should happen every few hundred miles.

Done about 70 miles with modified DPF and waiting for the warning lights to appear...
From VCDS I can see:

Soot loading has fallen to zero.
Differential pressure was 28mBar at idle now 7mBar. On the road anything from 50 to 600mBar, now 20 to 60mBar.
Done some logs before and after but not turned into graphs yet.

No regens yet. Should be a scheduled one every 300 or 400km. That could be interesting as it tries to get soot level down which is already 0.

I think the soot figure is low/off the scale as the stored ash value for the old filter is very high. The new filter should still soot up a little and should give the regen cycle some scope for a reduction in measured soot. But it is expecting to see a lot more back pressure all the time due to calculated ash. If I can reset the ash value to zero (new DPF) maybe all will be well.

Disappointingly, economy is not really much better. Getting 39 on 12mile run to work but this figure was a real struggle before.
Power delivery is a bit smoother but doesn't seem much quicker. Difference is i can give the car some stick now without provoking a regen. Before I got a regen started almost every time I put my foot down - which then made it run like dog.

Other things - I'm not seeing any smoke out the back and exhaust smells pretty clean. I now know the engine's not smoking badly so if worst comes to worst can always fit new DPF without clogging it - that was one of my worries.

If I get a bit more confidence ll is well I'l post a few photos and VCDS graphs.

Patrick

[a8 tech]

Check the injector fuel quantity and the valve timing as well because if the belt has been replaced and not aligned 100% on the camshafts this alters the critical timing and fueling.The engine will run the same but the valve timing angle required for dpf regen will not allow the dpf to reach the correct heat range.

[patrickhorton]

Not sure how to know if injection quantity is ok. Plenty of VCDS blocks to show quantity but don't know if right or wrong. Cam belt done 60k ago (12months) - can't imagine the effects of mistiming would take this many miles to show themselves. Presumably valve timing is a mechanical check? Don't mind doing this.

Car running lovely today averaged 44mpg of four mixed 12mile runs. This is what I was hoping for. Perhaps it's just the nice spring weather??

Regarding temperatures for regen - 800degC was always held rock solid during regen. Presumably this is the heat range referred to.

Another point of interest... a reason for sorting the DPF was rising oil level. Drained half a pint about 500miles ago and it returned to the same high level so took out a bit more last weekend and now it's holding steady. Theory is this was due to overfrequent DPF regen. Will keep an eye on it and will give it an oil change once DPF business is settled.

Patrick

[a8 tech]

Ok the timing should be fine but if the oil level increases on the dip stick then this is a sure sign the tandem pump is leaking causing fuel and oil to mix which either returns oil to the fuel tank or fuel into the sump