[Kfoehrkolb7860]

Hey guys how’s it going. Recently bought a 2011 Audi tdi wagon. On my way to work the other day it started sounding a bit more knocky than usual under light acceleration and under 2k rpm. Well after sitting at work all day it was hard to start and ran rough the whole way home. Hooked it up to VCDS and the only engine code it has is a bad o2 sensor. Fuel filter is new less than 1000 miles ago. Along with the engine oil and filter. Where should I start?
thanks!

 

[a1979corvette]

You will need to find out where the noise is actually coming from. I have a mechanic stethoscope scope to listen to engines. In the event you don’t have one, you can use a long screwdriver and place your ear on the end of the handle.
Google this:
How to use a giant screwdriver to find car noises

Could be worn camshaft and/or bad cam followers (very common), bad connecting rod bearing.
How many miles on the timing belt? Factory 80K replacement…
Does the engine still have the same amount of oil in it since the oil change?

 

[Kfoehrkolb7860]

So I can only get it to replicate this noise when the engine is under a load. I’ve done the trick your talking about before but usually with a long wooded handle Lol. Also it only does it every now and again it’s not a consistent noise. Pretty sure it’s a fuel knock of some sort but not sure how to diagnose that. Timing belt was done at 100k so I was told. Car has 128k on it now. Engine oil is still up it’s not eating or making any fluids.

 

[a1979corvette]

You can hook VCDS up and DATA LOG until it happens, then review that data.
If the timing belt was replaced by a tech, your car would have a label, like an oil change label. Normally they put this, in your owners manual, or on the timing belt cover, or under the hood at the front of the engine somewhere. If you can’t locate this evidence of maintenance, it didn’t happen.

My experience leads me to:
inspect the camshaft.
Under load, a worn camshaft and follower would tap pretty loud, cause loss of power.

Note: The injectors, valves, valve springs, camshaft, camshaft followers are all in the same location. Under the valve cover. Any noise from the valve cover could be anyone of those.

If you are absolutely, 100% positive it’s diesel knock, you can try replacing the fuel filter,
use Liquid Molly diesel purge to clean the injectors,
replace all the injectors
replace the tandem pump

 

[Lenct1951]

Hey guys how’s it going. Recently bought a 2011 Audi tdi wagon. On my way to work the other day it started sounding a bit more knocky than usual under light acceleration and under 2k rpm. Well after sitting at work all day it was hard to start and ran rough the whole way home. Hooked it up to VCDS and the only engine code it has is geometry dash lite a bad o2 sensor. Fuel filter is new less than 1000 miles ago. Along with the engine oil and filter. Where should I start?
thanks!

To start troubleshooting the problem, I would recommend checking the O2 sensor and making sure it is functioning properly. If the O2 sensor is not the issue, you might try checking the fuel system and the engine for any other problems. A mechanic or a dealership would also have the tools and expertise to help diagnose and fix the issue.

 

[Bernie-san]

If you previously did a VCDS scan prior to the issue you are having and did not have any codes then I would agree with Lenct1951 in his post about the O2 sensor. If you did not scan prior to the issue, clear the code and see if it comes back.

 

[Kfoehrkolb7860]

Hey guys finally got around to putting the o2 in my car. It’s running a lot better but the knock is still there. Attached is a picture of my injector IQ cylinder 3 shows -40 what’s everyone think?

 

[a1979corvette]

In your scenario, a negative reading means the computer is trying to reduce fuel to that injector by 0.38 Milligrams/ per Stroke (Mg/Str) Could be faulty/leaking injector #3 cylinder. You can inspect the glow-plug from cylinder #3 and #1 and compare them.
I would expect to see a sooty black, maybe wet with fuel or oil, glow-plug out of #3 and #1 glow plug should look remarkable better.

 

[Kfoehrkolb7860]

Just got my #3 injector flow and leak tested. The results came back near perfect… what else could cause the computer to try and pull that much fuel?

 

[a1979corvette]

I would have mentioned to the tech that flow tested the #3 injector that it was -0.47 Mg/Str off from #1 and #2. The tech would have wanted all 4 of them for the test. They should be within 0.15 Mg/Str +/- of each other.
Regardless.
Other things to consider for diesel fuel knock:
leaking exhaust valve
Bent valve
Low cylinder pressure/ incomplete combustion

If that doesn’t work, it may not be fuel knock.
In that case I would try adding
Lucas Oil 5.25oz Fuel Treatment
to your tank. This will lubricate and sometimes silence noisy injectors. It is noticeable in 5-10 miles of driving. After that and you see no change. You can also try adding a quart of Lucas Synthetic Oil Stabilizer to the engine oil Note: you will have to remove a quart of oil, before you add it and don’t overfill the engine oil. This stuff will silence and bearing or engine noise. The idea here is process of elimination. Eliminate a possible fuel noise or eliminate a possible engine oil system noise.
While they are not cheep products, It’s cheeper than an engine tear down and you eliminate fuel and engine oil systems as suspect. In my experience one or the other works. Then you know where to hunt the noise, specifically.
Another member of the forum will have to chime in. That’s about all I can offer with what we know.