Diesel Engine Knocking: Causes & Solutions

My Passat TDI 110 HP - AFN engine - has recently started making more knocking noises when it's warm, compared to when it's cold. (When it's cold, you can barely hear any knocking, but when it's warm, it gets a bit louder). Otherwise, I have no other problems with it; it pulls like it always has. Does anyone have any idea what this could be due to? Normally, it should be the other way around. ??? Thanks for your tips. Stroggi

Have you perhaps been tinkering with the air filter? In my case, after removing the intake manifold to the air filter box and then reattaching it, the rattling started, and it was extremely loud even at idle. The TÜV (technical inspection authority) even commented on it, but couldn't find the reason for it !!!

Hello,

Loud knocking always indicates poor combustion! There are many possible causes, but if it's worse when the engine is warm than when it's cold, I suspect the fuel injectors. Have the spray pattern and opening pressure of the injectors checked by a Bosch service center.
Other possible faults include: a defective fuel injection pump (high-pressure section leaking, causing warm diesel to bypass the plunger), and a misaligned fuel injection pump.

Did you perhaps tamper with the air filter? In my case, after removing the intake pipe to the air filter box and hammering, it started making a lot of noise, and it was extremely loud even at idle. The TÜV (German technical inspection authority) even pointed it out, but couldn't find the reason for it. !!!}

I haven't done anything like that with the car before. I'll check the connections of the intake manifold, though. Thank you very much.

Hello,

Loud knocking always indicates incomplete combustion! There are many possible causes, but if it's worse when the engine is warm than when it's cold, I suspect the injectors. Have the spray pattern and opening pressure of the injectors checked by a Bosch service center.
Other potential issues could include: A faulty fuel injection pump (the high-pressure section may be leaking, and warm diesel fuel may be flowing past the plunger), or a misaligned fuel injection pump.


If it gets worse, I'll have Bosch check the fuel pump and injectors. Thanks for the tip.