Hey all, I'm hoping there's some VAG engine experts here who can help me pin down the engine issues on my 2012 1.6tdi. I've run what diagnostics I can with Car Scanner and I think it's pointing towards injector failure (I'm aware this engine is prone to them), but Diesels are not my area of expertise so the numbers aren't that meaningful to me. I'm hoping some of the kind folks here with more experience on this engine might be willing to look over the results (attached) and offer some insight.

 

These are the spec & symptoms:

 

2012 1.6tdi, around 118000 miles. Bought the car in July and had zero engine issues up to this point. (Typically they began just one week after my 6 month warranty expired 🤦🏻‍♂️). Noticed a rough idle at startup one afternoon with a slight knock which got worse over the next 24 hours (3 trips, total of around 15 miles urban driving), the general symptoms are: The engine has a loud knocking at about half the frequency of the rpm. It idles roughly after starting, but this settles to a steady 750rpm after 30 secs to 1 minute. The knocking remains consistently loud and increases in frequency proportionally with the rpm. There are no warning lights on the dash and no engine/fuel related fault codes indicated in Car Scanner. No sign of any excessive or unusual exhaust smoke and no significant loss of power that I noticed, although I haven't driven it since the issue appeared.  In general the diagnostics seem to show one injector over fueling, one under fueling, but not massively and the fuel rail pressure is high and fluctuating significantly. The numbers are in the attached pdf.

 

I'm steadily mentally working myself up to forking out a large chunk of cash for one or more new injectors or a new fuel pump, but if you can tell me it's something less expensive I'd be much obliged lol. Thanks in advance.

Octavia Diagnostic Data Report v1.pdf

The only thing I can relatively reliably link to a failing injector is a loss of power (e.g. when accelerating up-hill in a low-speed area) - in my case it was the mechanical part that was about to fail for the 1 injector for which I have this analysis. With the last injector I could also invoke an apparent lack of power - accelerating from 60kph in 4th shouldn't have felt as impossible as it felt. Only this time the failure occurred before I could even downshift.

 

How can you notice no loss of power without driving the car?

 

Your car is about 13 yo - do you know if the cam belt has ever been replaced already? And what about the clutch? Those could definitely explain rough running and knocking AFAIK. An injector failing intermittently so not all cylinders are firing all the time could too, but that ought to register as a fault somewhere if it happens as often as you seem to imply.

Thanks for the response, I appreciate your input. I haven't noticed any significant power loss, but that being said I haven't really driven the car properly since the problem fully manifested, just a couple of short local trips at >50kph.

 

I hadn't considered clutch as a possibility, but nothing else really indicates that it might be as far as I can tell. Unfortunately I've only had the car around 6 months and service history prior to that is patchy at best so I've no real idea if the cambelt has been done on schedule or not, but I know there's a chance a failing cambelt could be throwing out the timing. However, like I said, my knowledge of diesels is limited, but the high pressure fuel pump performance is clearly all over the place, which is what leads me to suspect the issue is fuel system related. The fact that the issue came on quite swiftly led me to think it might just be a clogged injector, but I'm pretty sure that wouldn't be leading to over fuelling, which seems to be the case in cylinder 4.

 

I've got it booked in at the local garage on Tuesday. They've got a good rep, so hopefully they'll be able to figure it out pretty quickly, but I'm still open to suggestions from folk here who can offer some insight. 

 

Thanks again.

Re: the cambelt: I just asked my mechanic about his opinion on changing it on my partner's 1.0TSI Fabia. He looked up the official interval, which is apparently set at 120000km and he wouldn't say "yeah, sure" when I asked if we could postpone it until the easter holidays with the car already at 129k. Another one was present when I asked, and both confirmed that the cambelt doesn't give (much) advance warning when it's failing, and apparently you really don't want that to happen.

 

I guess the question here is what drives the fuel pump. If that's got its own electric power and doesn't maintain a steady 200 bar or so which I've heard cited for the pressure at the injector input, then that could well be the source of your troubles too.

 

There are others here who are much better informed on this sort of thing than I am.  I just learn this sort of stuff when something goes wrong