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D3 - Fuel and Exhausts Everything to do with getting fuel into the engine, and fumes back out again

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Old 11th July 2020, 07:59 PM
ainarssems ainarssems is offline
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Default D3 4.2TDI DPF issues

My D3 is about 175k miles now and as far as I know on original DPFs. A while ago glow lug light came on and there was an error regarding DPF pressure sensor, no effect on performance. I cleared, gave it some beans and it's been fine for about 4 months, error not coming back. I know previous owner replaced a sensor or 2 but there is 4 of them. They are not that expensive but located above gearbox so to access you need to drop subframe with gearbox/engine.

Then couple of days ago I joined dual carriage way full throttle - glow plug light came on again and lost power and max 2.5k rpm. I had to embarrassingly after overtaking everyone pull back in first lane and let everybody by Cycling ignition did not help. This time it came up with DPF efficiency threshold error. Clearing error restored power but going full throttle would bring error and limp mode back. I checked soot values and they were 18-19g calculated and 14-15g measured which is well within limits. I assume because soot is low ECU does not start regen but DPF is partially blocked by ash which does not burn off during regen or maybe oil residue or something, or pressure sensors give wrong readings so at full throttle with a lot of gasses trying to flow through DPFs there is too much pressure differential and it throws fault code.

Anyway did forced regen and then some 20 mile drive in 4th gear, this brought soot level down to 8g calculated, 4g measured, then raised back to 8-9g both calculated and measured. It now works fine and and does not go in limp mode even at full throttle but I think the DPF days are numbered.

So I am thinking DPF removal and remap is in order. Can anyone recommend a place in Midlands, preferably with dyno as well. I see MRC did 2007 Q7 4.2TDI remap about half year ago and got 416PS 957Nm( does not mention anything about DPF) which is quite impressive considering most tuning places only say 375PS. Not sure what it cost but I guess MRC are not cheap.

Depending what the cost difference is I might gut the DPFs myself and just go for remap but would prefer it all to be done by someone else.
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Last edited by ainarssems; 11th July 2020 at 08:02 PM.
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Old 11th July 2020, 08:04 PM
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homer simpson homer simpson is offline
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A lot of places used to do this modification but it has been illegal for a while now so not sure which garages still do this. Even if they do, they are unlikely to advertise it. It is also an MOT failure as the checks are more stringent so not sure if a missing DPF still passes if remapped out.
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Old 11th July 2020, 08:16 PM
ainarssems ainarssems is offline
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Quote:
Originally Posted by homer simpson View Post
A lot of places used to do this modification but it has been illegal for a while now so not sure which garages still do this. Even if they do, they are unlikely to advertise it. It is also an MOT failure as the checks are more stringent so not sure if a missing DPF still passes if remapped out.
It's not illegal to remove it, you are just not allowed to use it on road with modified emmisions sysetem. Regards MOT - yest it's a failure if they know it should be there and they can see it has been removed but normally you leave the can in place just take the guts out either cutting it open on the top where it cannot be seen and welding back up or braking it up in pieces and just pouring out of one end. And you can easily pass smoke test without DPF. My A6 without DPF passes Fast test with about 30% of the smoke limit first try every year. Fast test is the same for all cars DPF or no DPF, if you fail fast test then they look if your car is allowed more smoke.
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Last edited by ainarssems; 11th July 2020 at 08:21 PM.
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Old 12th July 2020, 02:31 PM
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A regen can’t get all the ash out of the DPFs once they’ve aged significantly - it burns off a lot but over time the nooks and crannies fill with ash. Best bet is to take them off and have them chemically cleaned. This removes the ash and restores them to good as new

DPF removal ought, by now, to be considered socially unacceptable, given what we know about the effects of PM10 and PM2.5 on long term health and air quality

Although MOT can be ‘dodged’ still, to a degree, there are still technical moves planned for MOT that will detect smoke opacity levels that exceed whatever is quoted on the VIN plate (number inside a square box, or default values). That may be a factor while the car is still on the road

Given DPFs don’t restrict engine performance to any great degree, chemical cleaning is the cheapest option without leaving a trail of smelly diesel fumes behind you
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Old 14th July 2020, 10:11 AM
ainarssems ainarssems is offline
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Just a bit of update. Had another occasion of limp mode after heavy throttle and DPF efficiency below threshold error bank 1. Checked soot values and pressure differential straight after and both were within limits. Soot 10-14 out of 68 for full DPF and pressure differential -7..+7 in idle, 7-21 driving, up to 160 full throttle, I understand max limit at full throttle with full DPF is 250mBar. So a bit puzzled why it's throwing up error, could be intermittent fault with one of sensors. So considering a sensor replacement I was looking into doing adaptation for new sensors or to reset DPF ash values if I go down DPF cleaning route.

It turns out that it is not possible with factory firmware and I need to update firmware first. I have stock firmware ending with 10 and I see there are 20 and 40 updates available ( not sure what happened to 30 )and there might be newer updates available. Previous owner told me he had some DPF pressure sensors replaced but since the car is still on stock firmware adaption for them could not have been done. I wondering if the sensors have been reading wrong and doing regeneration at wrong times. It's showing 600+km since last regeneration, it has not registered the forced regeneration I did, it was definitely doing it but maybe stopped half way before completing it.

It could even be something entirely different, I understand MAFs, ASV, EGR, exhaust temp sensors, all of them are also tied up with DPF to calculate the volume of gasses flowing through DPF and any of them not working properly could cause DPF errors but they seem to work OK.

I think I will just carry on resetting fault when it appears and let it develop further for now. In the meantime might look at flashing new firmware, I have ODIS, VAS5054 and firmware files but there is always risk when flashing firmware and I do not want to brick ECUs or run into security/immobilizer /component protection problems after update.
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Old 14th July 2020, 12:25 PM
paulrstaylor paulrstaylor is offline
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It has been a long time since my DPF issues on a D3, mine was a clear sensor issue and was resolved by replacing both sensors. Back end of the gearbox had to be lowered, not too bad with a ramp but clearly not going to happen on my drive!

The advice at the time was to ditch the DPFs, I wanted to keep them intact.

New sensors plugged in, problem resolved - no firmware issues, no remap needed - no re-occurance and reliable for at least another 60k until I sold the car

http://forum.a8parts.co.uk/showthread.php?t=4917

The thinking at the time was fix it sooner than later, as without regen the DPF more likely to end up stuffed up!
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Old 16th July 2020, 05:11 AM
ainarssems ainarssems is offline
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Well it has been gradually getting worse, happening more often and even at part throttle, seems to happen more when cold. P2002 error was accompanied by P2453 and P2454 this morning, pointing towards sensor. I have checked old paperwork and bank 2 sensor was replaced in 2016 for 252 and it is bank 1 playing up now. I have ordered new sensor, hopefully will arrive by Saturday and I will have a look if I can replace it myself over weekend.
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Last edited by ainarssems; 16th July 2020 at 07:55 AM.
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Old 16th July 2020, 06:51 AM
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Interesting read given I’m at the same mileage (on my 3.0).

Symptoms sound similar, bar the fault codes, to when my turbo suffered carbon build up and went into limp mode.

Keep us posted with your progress.
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Old 16th July 2020, 10:00 AM
paulrstaylor paulrstaylor is offline
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On the 3.0 the DPF sensor is easily accessible on the firewall at the rear of the engine.

On the 4.2 they were clearly struggling with packaging, so they fitted them on top of the transmission.

30 mins to replace on the 3.0, officially gearbox out and ~8 hours on the 4.2

Last edited by paulrstaylor; 16th July 2020 at 06:16 PM. Reason: spelling!
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Old 16th July 2020, 10:01 AM
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Quote:
Originally Posted by paulrstaylor View Post
On the 3.0 the DPF sensor is easily accessible on the firewall at the rear of the engine.

On the 4.2 they were clearly struggling with packaging, so they fitted them on top of the transmission.

30 mins to replace on the 3.0, oficcially gearbox out and ~8 hours on the 4.2
Cheers Paul. Ouch
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