Loud Engine Noise: Help! Nail/Knock Sound?

I'm completely desperate; my engine is making a very loud knocking and rattling noise, but...
Normal driving performance, but there's a rattling sound in certain RPM ranges.
almost unable to listen.
The very loud clattering sound is definitely coming from the engine.

VW believes the catalytic converter has failed, but that's not actually the case - ATU confirmed it.
The exhaust system has been checked and it can't help anymore either -- sigh.

Can anyone give me a tip?!?

OKAY: Passat TDI 110 hp (3B), year of manufacture 1997, 204,000 km.

Hello,

Unfortunately, you haven't written anything about your vehicle; no one can read minds.
Hopefully, you've already checked that nothing is loose on the engine mechanically, as well as the tensioner pulleys for the timing belt and any serpentine belts (if present).
What vehicle? Engine code letter? Mileage? Oil consumption? Recent repairs performed?
Have you checked the injection timing using a diagnostic tool?
When does the knocking/rattling occur less? Is it related to cold or warm engine temperature, low or high RPMs, or low or high torque output?
How is the starting behavior?
Questions upon questions... so go ahead and ask!

Best regards, Rainer.

Hello,

Unfortunately, you haven't written anything about your vehicle; no one can read minds.
Hopefully, you've already checked that nothing is loose on the engine mechanically, as well as the tensioners for the timing belt and any serpentine belts (if present).
What vehicle? Engine code letter? Mileage? Oil consumption? Recent repairs performed?
Have you checked the injection timing using a diagnostic tool?
When does the knocking/rattling occur less? Is it related to cold or warm engine temperature, low or high RPMs, or low or high torque output?
How is the starting behavior?
Questions upon questions... so go ahead and start!

The A.T.U workshop checked everything from the outside, and the noise is coming from inside.
Stand besonders laut, bei ca. 2500 Umdrehungen klappert es fast nicht mehr. Ansonsten ist eigentlich alles im grünen Bereich. A diagnosis.
It hasn't been done yet, but I will go to the workshop again tomorrow.
to rattle.
Volkswagen Passat 1.9 TDI 3B 110 HP, 205,000 km

Okay, a Passat TDI is already something, and what else?
Are the motor mounts in good condition? To check them, engage first gear, turn off the engine, open the hood, and then push the vehicle firmly forward and backward.
We are observing how much the engine tilts.

Best regards, Rainer.

Check if the alternator and power steering pump (if equipped) are securely mounted. I once lost a mounting bolt for the alternator.

Best regards, Rainer.

Okay, a Passat TDI is already something, and what else?
Are the motor mounts in good condition? To check them, engage first gear, turn off the engine, open the hood, and then push the motor firmly forward and backward.
We are observing how much the engine tilts.

Greetings, Rainer.

I forgot to mention that the Passat has a 4-speed automatic transmission.
has.
The sound is coming from the engine casing - *sniff...*

If it only occurs at very low speeds and disappears later at higher speeds, you should specifically check the front drive belt, especially the tensioner damper (a spring with an internal damper). A defective damper will make a noticeable rattling noise.

If it only occurs at very low speeds and disappears later at higher speeds, you should specifically check the front drive belt, especially the tensioner damper (a spring with an internal damper). If the damper is defective, it will make a noticeable rattling noise.

Good tip - thank you - I will check it out right away. }

I had the same thing last week.

You could only see it on the stage, and we didn't even realize what it was until an hour later. It was a bolt from an engine mount. It had come loose, which caused vibrations, rattling, and clunking noises.

Try getting on a lift, leaving the engine running, and then get underneath it to try and listen where the noise is coming from.

Could you try hitting it with a hammer? If it makes a noise when you hit it there, then it's definitely broken.

Otherwise, as Rainer already mentioned. Check the screws on the power steering pump, alternator, transmission, etc. Pay particular attention to those that are attached to the engine mounts, as described above.

Perhaps the exhaust pipe is rattling, but you wouldn't notice it when it's on the stage because the axles aren't under load and are in a different position than they would be during normal operation.
Perhaps it's the exhaust pipe attachment point at the rear axle.

I know how to drive someone crazy.
Arne.

Hello Rainer,


Are the motor mounts in good condition? To check them, engage first gear, turn off the engine, open the hood, and then push the vehicle firmly forward and backward.
We are observing how much the engine tilts.


I once tried this on my car (which tends to rattle quite a bit) and managed to get it about 3-4 cm.
Do you (or someone else) have any idea how far the motor is allowed to move ?

Hi!

It's also possible that the turbocharger has internal damage. This can cause rattling or knocking noises, and it won't necessarily reduce power if it's still spinning. What is the exact relationship between the noise and the engine speed?

Best regards, Uwe.

Hello Rudi,

Mine also moves about the same distance!

Hello Rudi,

You can't just say that in general; it also depends on how firmly you push things back and forth. In any case, nothing should be loose or able to shift around.
In my case, it was clearly visible that the engine mount on the left side (facing forward) had shifted its position on the engine side, which is not supposed to happen. Consequently, it tilted more than your reported 3-4 cm.
I then disassembled the casing and added an extra rubber strip because the rubber inside was somewhat crumbly/worn out.
Since then, he's been driving more calmly, and there are no more noises coming from the car.
Ideally, a new engine mount would have been the best solution, but if it works this way too...

Best regards, Rainer.

Hi,
Thank you for your quick response.

@Uwe:
It usually rattles at low speeds/when starting.

@Bertil:
Then, at the very least, the range of motion due to the motor mounts is 'normal.'
(or yours has the same quirk ).

@Rainer:
ich muß am Wochenende sowieso Öl wechseln. WLet's take a look.
How the rubber looks.

Rudi wrote:

Hi, @Bertil: Then, at the very least, the range of motion due to the motor mounts is "normal." (or yours has the same quirk ).

"Um... when I attach the trailer hitch, something hits the engine or something nearby and makes a noise. I haven't been able to find out what it is yet. The engine mounts are all new except for the one near the turbo."