A6 / C6 - 2.0 TDI (BRE) Serious Engine Problem - Serious Underperformance Issues

[Crasher]

Whenever I get running problems on any engine, I always look into the service history for clues.

[Overdose]

I have just resolved one of my ongoing issues with my Caddy for a very similar situation. I had similar symptoms to the OP, but my problem was compounded by a camshaft sensor fault. Initially I had an intermittent no signal fault and hard starting when hot, all indications suggested the cam sensor, so it was duly replaced.
The replacement cleared the intermittent no signal, but introduced a consistent "implausible signal" at around the same time, the car became difficult to start, hot or cold, mpg dropped significantly and the engine stuttered and suffered from power loss. VCDS showed an implausible signal with 0º-62º torsion values, constantly fluctuating.
I spent a fair amount of time investigating the fault and could see no wiring loom issues in the typical weak spots at the front of the engine, so decided that the new sensor was at fault. I changed this for another today and had a major improvement, the torsion values moved to -2.5º, but the implausible signal remained. I still might have a wiring issue elsewhere, closer to the ECU or the ECU might itself have a problem, but the sensor could also be a bit dodgy, as it isn't OEM. All readings seem to suggest that there is a good signal, however.
Moving on to the rough running:- After the sensor was replaced, I took the car for a run and the engine was still struggling, being quite noisy and obviously labouring as well as being under powered. Seeing this thread reminded me to check my service details and found that it was serviced in August, with less than 6K done in that time, so everything should have been fine. The thing is, it wasn't fine and the filter was as black as I've ever seen a filter be, except for an oil filter. Almost certainly, this is the cause of the loss of power and general engine rough running, but the cam sensor fault threw me off course.
There are a good few lessons to be learned from this.
1. Don't assume that a replacement component is always fully functional.
2. Don't cheap out on sensors, buy good quality, if not OEM items themselves.
3. Sometimes it's easy to overlook the obvious, bring diagnosis back to basics before jumping in to replace components.

Another thing that might be interesting for some, is that how quickly the filter almost completely clogged. I have no real way of knowing for sure, but one of two things springs to mind as to why.
1. The recent fuel shortages have most likely meant that forecourt tanks have been frequently drained down almost entirely and then refilled, stirring up sediment at the bottom of the tank and creating dirty fuel at the pumps.
2. The same fuel shortages might have led to less than ideal quality fuel, being pushed out to shore up supply.

Anyway, the pic below is actually my fuel filter and not oil...

IMG_2076.jpg

[rjsdavis]

The thing is, it wasn't fine and the filter was as black as I've ever seen a filter be, except for an oil filter. Almost certainly, this is the cause of the loss of power and general engine rough running.

Another thing that might be interesting for some, is that how quickly the filter almost completely clogged. I have no real way of knowing for sure, but one of two things springs to mind as to why.
1. The recent fuel shortages have most likely meant that forecourt tanks have been frequently drained down almost entirely and then refilled, stirring up sediment at the bottom of the tank and creating dirty fuel at the pumps.
2. The same fuel shortages might have led to less than ideal quality fuel, being pushed out to shore up supply.

Anyway, the pic below is actually my fuel filter and not oil...

IMG_2076.jpg

I'm glad that you've got it sorted out, and am especially pleased, if my rather torturous thread has helped someone else! You can see what I replaced at the advice of garages - to no effing avail at all.

That's a very grubby fuel filter. You're saying that it's only about 8 months / 6k old? Ifso, that's far worse than it should be... What are the intervals on your Caddy for replacement? It was suspected that mine might have dated back to 2016 looking at the stamps on the side of the fuel filter. Mine is a non-serviceable enclosed unit, where you simply unhook the pipes from the old, slot the new in, and re-connect the two main fuel pipes. You can't see inside it. I'm sure mine looked worse than yours - but to be fair it had likely done 5 more years and probably 40-50k miles!

Presume you've now driven yours with the new filter in and it's cured your power problems?

[rjsdavis]

1. Don't assume that a replacement component is always fully functional.
2. Don't cheap out on sensors, buy good quality, if not OEM items themselves.

Also - Amen to that.

My son's MKIV Golf had an O2 sensor problem which VCDS and the dash were flagging. He ordered a Gen replacement from Deutsche Parts, mechanic fitted it - no joy... same problem. We bought a third sensor from a local factors, and it worked immediately and cured the problem.

The hassle we had returning the 2nd part back to Deutsche Parts though! They were so abusive, claiming that Gen parts are *never* returned to them! In the end we had to get the bank involved to force it's return through a chargeback. We then got an unbelievably snotty email telling my son to never buy from them again. Honestly, it was staggering, even with VCDS reports to support what we had experienced.

[Overdose]

Last service 7 months and 6300 miles ago. I did it myself, so know it was done right.

Very strange how the filter managed to get that dirty so quickly.

[Crasher]

Very strange how the filter managed to get that dirty so quickly.

The tandem pump is leaking engine oil into the fuel side.

[Overdose]

Thanks, so presumably a combined oil and fuel pump. I'd better have a Google...

Repairable, or replace? Also, easy to diagnose?