Dreaded DPF and possibly EGR cooler leak.

[marcc]

Evening chaps, I wonder if I may ask for a little help, please? I'm not one for just asking questions without scanning the web and racking my brain first, however I have done a fair bit of work on an attempt to resolve and so far, not made much of a difference. I am now about to pull my hair out.

Car in question: 2012 A6 C7, 3.0 TDI Auto Avant at 145k miles.

Main problem is a constantly blocking DPF. DPF light on dash, almost no power so I had it professionally removed and cleaned, along with EGR, this got it back on its feet in no time.

Fast forward a few months, same issue. I couldn't justify paying hundreds again so I flushed out with some Wynnes DPF cleaner, ran a VCDS regen and all working again, DPF light extinguished!

Fast forward a few more months, same again. I flushed again and dropped in a new set of glow plugs, all ok again. Checked injector values on VCDS and they seem to be within tolerance, although I'm not expert, reading another support thread, they seem ok. Cleaned out the EGR valve and pipes, they were clogged up with soot.

Fast forward again to now, blocked again and even though a flush and forced regen removed the DPF light on the dash, something doesn't seem right. I gave the car a good thrashing ok the M1 earlier while the Mrs kept an eye on VCDS for exhaust temps, soot values etc. exhaust temp one fluctuates but does get to 400+ degrees, much lower than the 800 I thought was needed for a regen but the soot does lower at a slow rate.

One thing I noticed is that if I drive at 70mph with revs about 2k, the soot slowly drops, if I give it some welly with the turbo active and revs 3500+, the soot starts to climb slowly.

Given the work I have done so far, does anyone think a bad turbo could be the culprit? Power generally seems to be fine, although poor when dpf blocked. I also have a small coolant leak, which I think it the EGR cooler seals, not sure if this is related. To make things worse and to add to the ever growing expense, the clutch is slipping, so it's having a new clutch fitted next week.

Any guidance would be gratefully received! There's no Haynes manuals for these, so feel a bit lost.

Cheers

[Crasher]

You can get a manual from Audi erWin (https://erwin.audi.com/erwin/showHome.do) and for €25 you can get 24 hours access where you can download all the dealer level information (except that provided by the ODIS system) and save it as a pdf file for future cost free access. My suspicion with yours, knowing this engine all too well, is that you have at least one injector with a poor delivery problem.

[marcc]

Super thanks Crasher, much appreciated 👍

I'll take a look at the Erwin link asap.

Interesting you say that about injectors. I thought I had eliminated these but I guess I had not tested them under heavy load, which is when the soot figures appear to rise. Not only that but the dpf problem seems to be more regular, so if it is one of the injectors then could be gradually getting worse.

I am not sure if the car been remapped and this is something this does raise a question too, although the car has been perfectly fine for the 5 years I have owned it, so leaning towards something that has failed, like an injector and not something intentionally done many years ago.

Thanks

[Crasher]

During a prolonged idle to you get any smoke or signs of a nasty combustion smell plus even the slightest increase in oil level?

[marcc]

I do recall a strong combustion smell when ticking over and walking about the car while unloading etc, strong enough for me to notice. Can't say I have seen any smoke either. One thing that I did notice, was a slight increase in oil, just after an oil change. I changed the oil and for the first day it was just below max on the screen, ever since then it's been at max! I put this down to the oil settling down.

Car gone for a clutch this morning, so won't see it for a few days, but will try and get VCDS reading of oil and maybe injector readings under load to show which plugs might be problematic, unless there's another way to check. I see injectors are eye wateringly expensive, so a test beforehand would be advantageous.

Cheers

[bluezie]

As Crasher said, you probably have a dodgy injector. The DPF should not soot up that quickly, and there should be no bad smells from the exhaust. I have the CDUD 245BHP version, and never had a DPF light despite repeated 2 mile short journeys. The exhaust is almost smell free when idling for long periods, and only smells of burnt toast during the not that frequent regen.
The non DPF 3.0 fitted to the C6 model, had umpteen revisions of injectors, as they dribbled, belched a bonfire of smoke at traffic lights, and filled the oil with diesel. Generally this was sorted by the C7 model.

If the exhaust smell at idle is a very nasty acrid smell that makes your eyes sting and throat sore, then very likely it's a bad injector. All the smoke is then clogging the DPF.

[marcc]

Thanks guys, really do appreciate your input. It's easy to take to garage and let them raid my bank at will.

Anyhow, just got car back from replacement clutch, gear changes are as smooth as now. The old clutch assembly was at 140k and smelt of burning apparently.

Interesting what you say about the injectors, I'll whip them out and have them tested. I did just call a local special and they want £35 each to test :(. Wasn't expecting that much to teat... I even asked if that was all of them, sadly not. Any way of testing them myself? Could they look damaged or faulty?

One quick test I did on the car last night was to disconnect the MAF, I had read if the car was mapped the disconnection of MAF sensor would not throw an eml, but it did throw eml after a while, so guessing not mapped. I must say, the car drove exceptionally well without the MAF sensor, in fact the car was so fast and responsive, it was like night and day, a totally new car.

[bluezie]

The injectors have to be tested on a proper rig, no way of telling anything just by looking at them. Rigs are not cheap, so yes it will cost to have them properly tested.
Disconnecting a MAF should throw a code, not heard of them being mapped out, well not on normal maps, possibly on extreme racing maps? But, disconnecting a MAF should give you less power, as the ECU substitutes a fixed lower MAF value as a limp home measure. If plugging the MAF in gives less power, that's normally indicative of a failed or dirty MAF. If you have VCDS or similar, you can log and graph the MAF readings to compare with the specification.

[Roverfan]

A pre dpf exhaust leak could also give unreliable regens

[marcc]

Cheers guys and noted on the exhaust leak. I think lifting the car for an inspection is in order to eliminate the exhaust and intercooler pipes etc.

On a positive note, thanks to your advice regarding MAF sensor, Bluzie. I just whipped off the MAF, gave it a few taps and a piece of chaff fell out. I gave it a good suck and blow as there's not much more I could do, plus wiping the dirt of that small, what I think is a thermistor then reinstalled. Well the results are truly unbelievable, full power restored! Truly amazed at the power loss such a small thing in the MAF has caused. Interestingly, the power issue was a little intermittent, so presumably the chaff was moving about. As of now, the car is performing very well :)

With regards to the injectors, noted, I'll get them out and tested before I take any more bank damaging action.

Cheers

[marcc]

Finally able to confirm that the dirt in the MAF was the root cause after all, that I am 100% sure of now.

With the dirty MAF I think DPF regen was taking place but as the MAF was giving bad readings, the fuel/air mix was all wrong, hence it would have been smoking up like a trooper while driving hard to force a regen on the motorway. Since cleaning the MAF, the car did it's own regen on the M1 and all seems to be running very well now ,all power restored. I still have coolant leak in the V but that's a job for another day.

Not sure if you guys know of VAG DPF app in Android app store, but I started using this so I could see live data while driving, without the need for vagcom/laptop on the passenger seat. Finally I could see live data and more crucially, the DPF temp, post injection and the regen status - highly recommended! you can actually see the DPF hitting 600+ degrees, post injection kicking in and the soot levels plummeting while driving, very reassuring to see.

Thanks for you help again chaps, much appreciated.


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