2005 B5 Passat TDI Loud Clunk Under Load Then Loss Of Power

Alright, I am at a loss with my problem in my passat.

It is a 2005 B5 2.0 TDI Auto

When under load something pops or clunks really pretty loud on the drivers side of the engine then it sound like louder knocking and or louder air noises. It also has substantially lower power during this time and idles/runs much rougher. Once you let off and go back it idle it sounds like a spinning clunking noise then a final clunk and it goes back to running fine as if nothing was wrong at all. Its gotten worse and worse to where I just parked it and stole the wifes 2019 Jetta to commute with haha. The motor mounts are suspect a bit but I highly doubt they are causing this issue. This sounds like internal engine/trans noises when it happens. Definitely rpm/load induced. You can also duplicate the symptom if you rev it hard it park and let off fast.

I havent been able to find anyone else with these kind of symptoms. I will say that previously I did have the dash flash for emissions stuff. But it would come up then just go away on its own.

This car has some work done to it.
Balance shaft delete
Stage 2 tune
ect ect.

Approximately 250k miles.

Perhaps a mount is broken and it has been pulling a charge air tube loose. That is where I would be looking.

oilhammer said:

Perhaps a mount is broken and it has been pulling a charge air tube loose. That is where I would be looking.

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I've watched some vids of broken motor mounts ect. But this clunk noise sounds much more mechanical then a motor bumpin around some. Ill have to take a video, might make more sense than my babbling haha

Maybe double check if the over running alternator pulley isn't going out.

Maybe the CV Joints are going? They can make alot of noise when failing. These will be wheel speed dependent, not engine speed dependent.

Lotawood said:

Maybe double check if the over running alternator pulley isn't going out.

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That actually does sound plausible, I will check that. Thank you

deckerfl said:

Maybe the CV Joints are going? They can make alot of noise when failing. These will be wheel speed dependent, not engine speed dependent.

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I can replicate the issue while sitting still in park by reving up close to the redline then immediately letting off. It will almost do it right away if you load the engine in drive and apply some skinny pedal. Ive been messing with cars my whole life and Audi's/VW's for the past 10-15 years and have never came across these kind of symptoms.

You could get lucky if its alt pulley, very easy to change.

Is your front snub mount in good shape? The will dry rot and just disintegrate which would leave metal on metal bumping when under load or coming off load. Can and will take out the other mounts over time.

Recently had someone ready to replace all the control arms because of an odd noise and found the transmission mount shot. It fixed his problem.

I suggest you start by having someone rev the engine while you stand next to the car and observe how much the engine moves. Then have them hold the brake, put the car in gear and push the diesel pedal and see how much the engine moves. Lastly, inspect/replace engine, transmission and snub mounts as needed.

A few notes:

1. Sometimes, just looking at the mounts doesn't give you the full picture of the condition. Best to remove and inspect.
2. If the part # on the side of your engine mounts do not end in AR, you do not have the latest version.
3. Only get VW OEM engine mounts if you need them.

None of this explains the power loss, other than what Oilhammer has suggested.