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

[rjsdavis]

In your post you mention " and a occasionally temperamental oil sensor " although it doesn't show in your VCDS log.

If it were a low oil pressure warning I could see that putting the engine into limp mode, although I don't know that for a fact.

EDIT Sorry, just noticed it in Instruments - 00562 - Sensor for Oil Level/Temperature (G266)
010 - Open or Short to Plus

So probably not relevant.

Thanks Philip

I don't know if it's relevant or not - as I think it's an electronics gremlin. It used to happen quite often, when I had the massive power drain issue, that was actually being caused by a faulty Control Head (which I tracked down and replaced), so I hadn't actually seen this little glitch for the best part of two years. It's happened a few times last week. It happened every day, every engine start for about three or four consecutive days, and then simply stopped.

The yellow alert on the dash would usually disappear within a few minutes of driving, or the engine simply running... now that I think about it, I am seeing one or two of the same glitches from this period. They were:

* Oil level sensor warning on the dash
* All of the MMI lights on the centre console refusing to light up occasionally (that is to say, all of the MMI buttons that light up red around the gearstick, were simply all off (the MMI system was still working fine though)- an engine restart always cures this gremlin)
* The MMI system would go haywire and require a manual hard reboot (this one is unsurprising given the Control Head was the faulty unit)
* HVAC pressure sensor code (on VCDS)

It seems unlikely to me that they're interconnected with the present engine issue, as they all disappeared when the control head was replaced. It does smell very slightly that the replacement Control Head might, just might, be starting to cause me a brand new slight issue - although unlikely. The car is shutting down fully when the engine is turned off and car locked, but I will keep an eye on it, just in case.

[rjsdavis]

I would be doing a requested and actual boost graph.

Hi Crasher

Already have - but unable to upload the csv file into here. This is how I know that there is massively erratic variation in the expected -v- actual pressure numbers on the turbo. The garage I was using got the exact same results when they tested the car, and couldn't understand why when the pressure variation exceeded 250 milibars, that the engine wasn't going into limp mode as its supposed to apparently. This was on a "3rd to redline turbo road test".

The readings between old turbo and replacement turbo follow the same erratic variation pattern when giving the car some beans. I'm not ruling out that the replacement turbo could also be a dud, but my gut tells me that it's something else.

For me, the most telling and head scratching thing, is when the replacement N75 solenoid was fitted - approx. 90% of engine performance was restored. If the turbo were the culprit here, the new solenoid would (imho) have made little to no difference at all right from the off. Something in the engine system then caused all of that performance restoration of the new N75 to be dissipated away in just one journey and over the course of about 60 miles. This is what blows my mind. I don't understand this at all....

If there's a way of uploading the csv data into this forum, please let me know. I also recorded the injection readings at the same time, but honestly don't know how to interpret them, or whether they're showing me something that is right or wrong! (For example, I can see that at least one of the injector readings have negative numbers, and others positive - but I don't know if the numbers or right or wrong...)

[Crasher]

I do it as a graph so I can show it to the customer.

[rjsdavis]

I do it as a graph so I can show it to the customer.

Sadly, that doesn't show the raw numbers.

I've tried to paste in the cells from my csv directly into a reply, but when you then try to submit the post, the website falls over, goes white, and does nothing. It won't work.

I don't see how I can share raw data if the website won't permit the pasting of spreadsheet numbers.... However, as I'm looking at the cells in more detail, and trying to interpret what they mean, I can see that I've captured "Injection Quantity Deviation" from all four cylinders, which are measured in mg/str.

There are positive and negative deviations in all four cylinders. I don't know if the numbers are significant though.... I notice that Cylinder's 2 and 3 initially have noticably larger deviations than 1 & 4. Again, I don't know if the measure of 2.99 or -3.01 are significant numbers?!? These numbers are just from ticking over at the start of the log. If I peel down the spreadsheet to around row 400, where the beans are given and the turbo pressure numbers go erratic, the injector deviation numbers get much smaller - down to 0.45 on Cylinder 2, and -0.24 on Cyl 3 - but Cyl 1 changes to -0.94 and Cyl 4 increases to 0.73.

I don't know what I'm reading, but they just don't seem right somehow...

For example:

TIME	Group 13 - Field 0	TIME	Group 13 - Field 1	TIME	Group 13 - Field 2	TIME	Group 13 - Field 3
STAMP	Injection Quantity - Deviation Cyl. 1	STAMP	Injection Quantity - Deviation Cyl. 2	STAMP	Injection Quantity - Deviation Cyl. 3	STAMP	Injection Quantity - Deviation Cyl. 4
	mg/str		mg/str		mg/str		mg/str
0.34	0.42	0.34	2.99	0.34	-2.85	0.34	-0.66
1.17	0.49	1.17	2.99	1.17	-3.01	1.17	-0.56
2.03	0.49	2.03	2.99	2.03	-3.01	2.03	-0.49
2.87	0.49	2.87	2.99	2.87	-3.01	2.87	-0.49
3.71	0.47	3.71	2.99	3.71	-3.01	3.71	-0.49
4.55	0.45	4.55	2.99	4.55	-3.01	4.55	-0.47
5.38	0.45	5.38	2.99	5.38	-3.01	5.38	-0.45
6.22	0.42	6.22	2.99	6.22	-3.01	6.22	-0.42
7.04	0.4	7.04	2.99	7.04	-3.01	7.04	-0.4
7.9	0.35	7.9	2.99	7.9	-3.01	7.9	-0.35
8.72	0.28	8.72	2.99	8.72	-3.01	8.72	-0.28
9.57	0.21	9.57	2.99	9.57	-3.01	9.57	-0.21
10.4	0.09	10.4	2.99	10.4	-2.99	10.4	-0.09
11.22	0.02	11.22	2.8	11.22	-2.87	11.22	0.02
12.05	-0.05	12.05	2.66	12.05	-2.73	12.05	0.14
12.87	-0.09	12.87	2.61	12.87	-2.68	12.87	0.19
13.73	-0.21	13.73	2.61	13.73	-2.64	13.73	0.24
14.55	-0.24	14.55	2.61	14.55	-2.61	14.55	0.28
15.41	-0.33	15.41	2.56	15.41	-2.56	15.41	0.35
16.24	-0.38	16.24	2.56	16.24	-2.54	16.24	0.35
17.08	-0.45	17.08	2.52	17.08	-2.47	17.08	0.4
17.9	-0.49	17.9	2.54	17.9	-2.45	17.9	0.42
18.74	-0.56	18.74	2.52	18.74	-2.4	18.74	0.47
19.57	-0.68	19.57	2.54	19.57	-2.38	19.57	0.52
20.42	-0.78	20.42	2.54	20.42	-2.33	20.42	0.54
21.24	-0.82	21.24	2.54	21.24	-2.31	21.24	0.59
22.07	-0.92	22.07	2.56	22.07	-2.24	22.07	0.64

[Crasher]

I am not interested in the raw numbers, just requested and actual making sense.

[rjsdavis]

I am not interested in the raw numbers, just requested and actual making sense.

So - what do you think it could be?

[Crasher]

As suggested it could be a blocked cat but it is a very rare problem, usually only after a misfuelling event. Can you do a group 011 requested and actually graph with a screen shot, set the time base quite slow and do a couple of 3rd gear WOT runs with someone holding the lap top and taking screen shots, try and get at least two runs on one screen shot, like this



Ignore the red rpm line and I tweak the scale to make it fit as sometimes the high points are off the page. The above was a Golf 5 GTI where the yellow requested was answered with a boost pressure that was all over the place, I can't find a Diesel one that I have saved.

[rjsdavis]

I'm delighted to report that the problem is now resolved.

Believe it or not - it was simply the fuel filter. I can't effing believe it.

The filter that came off was a gen VAG/Audi unit. It's not impossible that it's original, but whenever it was last changed, it wasn't changed by me. We couldn't see a particularly obvious date-stamp on the old one, but it did have "47 16" on it, so I'm not sure if they're week/year coded like tyres are.

After the new filter was on, we still spent more than an hour on the car looking for something - anything that was wrong and finding absolutely nothing wrong anywhere, until my friend suggested giving it a test with the new filter on. It was back to normal - and 100% from the first throttle. I reconnected the mapping box, and even more power has returned as well as my enhanced MPG.

Am very, very pleased and relieved that that was all it took to FINALLY get this engine running properly again. It's odd, and I don't know why I didn't look at it before, but I simply typed in "diesel engine power problem causes" (or something very similar), and the fuel filter came up in a number of places as one of the primary causes. If only I'd done this six months ago when it started to go quite wrong... FML!

Anyway, delighted that I've got a properly working car again. The absolute joy that it brings when you can accelerate up a hill!

[Gazwould]

Excellent news .

Now for the next fix .

MzVlNDk5N2E5M2RlYWI0MDY1YTcxZTk4ZDU0MWM0ZTgAwIu4Zi-i85cUctp5kaTFaHR0cDovL21lZGlhLmFkc2ltZy5jb20v.jpg

[dean warren]

I'm delighted to report that the problem is now resolved.

Believe it or not - it was simply the fuel filter. I can't effing believe it.

The filter that came off was a gen VAG/Audi unit. It's not impossible that it's original, but whenever it was last changed, it wasn't changed by me. We couldn't see a particularly obvious date-stamp on the old one, but it did have "47 16" on it, so I'm not sure if they're week/year coded like tyres are.

After the new filter was on, we still spent more than an hour on the car looking for something - anything that was wrong and finding absolutely nothing wrong anywhere, until my friend suggested giving it a test with the new filter on. It was back to normal - and 100% from the first throttle. I reconnected the mapping box, and even more power has returned as well as my enhanced MPG.

Am very, very pleased and relieved that that was all it took to FINALLY get this engine running properly again. It's odd, and I don't know why I didn't look at it before, but I simply typed in "diesel engine power problem causes" (or something very similar), and the fuel filter came up in a number of places as one of the primary causes. If only I'd done this six months ago when it started to go quite wrong... FML!

Anyway, delighted that I've got a properly working car again. The absolute joy that it brings when you can accelerate up a hill!

Oh glad you sorted it, looking at the depths you had already gone to I assumed you had already done the filter… lol never mind


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