Hi all,

My A4 1.8T is slightly over 70k. It has been given Shell V-Power and changed oil every 5K (using 0W30 German Castro) rigorously since 45K.

Recently (June-July 2010) the engine starts making loud knocking noise (not the ticking noise, but clear knocking noise) ONLY under the moderate load, particularly when driving on flat road with the 3rd gear @ approx. 2000-2200rpm. I once noticed the same knocking noise when I climbed a steep hill with the 1st gear @ around 2500-3000rpm with the clutch fully coupled. So the knocking noise may somewhat be related to the engine load.

But what makes it strange is that the noise would go off suddenly when I either release the gas paddle (understandably) or PUSH IT HARDER (that's where I got puzzled). If I maintain that particular engine load, the noise remains forever. To my understanding, if the engine is knocking due to a wrong timing or a carbon deposit buildup, the symptom would surely be aggravated when being pushed harder, right? But that is not the case.

The engine runs smoothly with no engine light, and has been treated with one run of Liquid Molly cleaning addictive with no sign of alleviation whatsoever. I doubt if it is caused by carbon buildup, since I have never put fuel below #93 into the car since I got it at 45K.

I tried Audi dealer and they couldn't find the problem but suggest it might be related to the hot weather temperature. Granted the temp is very hot in Toronto recently (above 30 C during the day), but I test drove it twice at night when temp fell to 25 Celsius but the problem remained (Psychologically speaking, the noise was slightly lighter, but still too loud to be anywhere close to normal). I also went to a VW-specialized mechanic shop where we lifted the car off the ground and applied brake while pressing gas to simulate a road load. We heard some noise, very similar to the engine knocking, but definitely not loud enough, from the ABS unit. We scanned the car for any ABS malfunction code but got nothing. I guess the noise from the ABS pump was simply caused by applying brake on empty wheel loads. It may trigger the ABS or let it behave weirdly.

Any one could shed some light? Thank you very much!

 

P.S. I forgot to mention something which might be important or helpful. The knocking noise was already audible last year in the Summer (I guess it was because I only drive with windows wide open during the summer so I could hear it) But the sound was very mild and came on infrequently. I could only very occasionally notice it when I past through quiet neighborhoods. The problem has turned a lot of worse since this summer...

 

Hi I have the exact problem! Cannot seem to resolve it. I doubt it is from the ABS. It is definitely from the engine itself.

Does anyone what a solution?

 

I wonder if you have a bad knock senor. I am sure by the sounds of your post it is a timing issue. I would check the knock sensor if you have not already. It should call a code (engine light), but it could still be working, but not properly, so I won't call a code.

Also, what type of fuel, octane wise, do you use. If you use 87, bump it up to 91 for two fill ups and see if that changes the knock and performance.

 

I use 91 and occasionally 93/94. I still have the issue. When it's cold there is no knocking sound. When it gets warm/hot it knocks when around 2000rpm when I press on the gas pedal. Somehow it knock more when it is real hot when driving in stop and go traffic.. I was thinking a defective Temperature Sensor or Knock sensor. There is no CEL light at all. Also when the knocking/pinging happens I notice the engine lacks power too.

Any suggestions?

 

sorry for the old thread bump...I've been experiencing the same sound for years and have not been able to pinpoint the issue.
Another B6 drove by me yesterday and was making the same noise! Is this common?

Any help would be appreciated