Mk5 GT impossible tapping noise

[Von]

Hi, since i purchased this 1.4 TSI BLG Mk.5 GT GOLF as my first car, I've been having problems with this tapping noise, it's only audible from 800rpm til 2k rpm.
This is a list of parts i have replaced in the last 4 months of ownership:
>2x Camshaft adjustment control valve
>2x Camshaft adjuster
>Camshaft position sensor
>Tappets
>2x Sparkplugs
>HPFP
>Piston Rings
>Rod Bearings
>and a few other sensors
Plus manual cleaning of the MAF, intake, throttle body, valves and such, however none of these helped even slightly and now the car is running worse than ever, i've had piston chamber compression tests done and they came out fine, with only one piston being slightly affected, it's running at about 80% what it should be, also oil pressure tests came out fine, they also said the timing chain system is fine. Something interesting happened yesterday, when I took out the Camshaft adjustment control valve and started the engine without it, the tapping was barely audible while close to the engine with the bonnet up, but as soon as you revved it the tapping came back, that got me thinking if its something electrical rather than mechanic, so i took it to an electrician who checked the ECU and told me everything was fine. This car has truly done my head in and the mechanics are sick of seeing it, how should i go about fixing it?   
Video of tapping noise:

[OllieVRS]

I don't know much about TSIs, but if this was the 2.0 TFSI I was straight away say it's a failing cam chain tensioner.

Can you pinpoint where the sound is coming from?

[Von]

I haven’t thought of that, but the mechanics said the noise is coming from somewhere under the engine.

[OllieVRS]

I haven’t thought of that, but the mechanics said the noise is coming from somewhere under the engine.

Has this sound been there the whole time since the engine rebuild? Or gradually developed?

Very unlucky that so much has gone wrong with this being your first car. The 1.4 TSI is known for being mechanically unreliable.

EDIT: Did the mechanic give a reason for the lower compression on one cylinder?

[Von]

Yeah i guess it is unlucky, to be fair though it doesnt take away from the driving experience, but safe to say i wont be buying another 1.4 tsi, i dont remember if they specified why that piston is behaving badly, right now i’m going to replace the timing chain and tensioner which will hopefully solve the problem, also they told me that my turbocharger axis is going too, so a new day, a new pain.
Edit: it was there since i bought it, the previous owner told me it was a tappet and i believed it because it really does sound like a tappet, so i went and changed them and even put hydraulic oil for tappets in it but it hasnt helped.

[Von]

UPDATE: So I have replaced the timing belt system, and the tapping isnt gone, but something i believe i forgot to mention, last time i checked the oil filter there appeared to be some silicone bits stuck to it, i believe the previous owner did some shady repairing with silicone and it ended up in the engine, so we went and checked the oil pump, which seems to be clogged, weird, because the oil pressure test was fine, now im going back and replacing the oil pump and the piston rod bearings.
Also, genuine question, since my turbo is pretty much done for, would a bigger turbo be an easy upgrade, or am i gonna have to replace injectors and so on?

[OllieVRS]

Usually bigger turbos means bigger injectors, plus necessary supporting mods such as intercooler, high pressure fuel pump upgrades etc. Otherwise you will gain little power over the stock turbo. So you have to factor the cost of everything in.

I would say unless you've got money to burn you should just get your current turbo remanufactured/refurbished.

Why do you want to replace the oil pump if it's giving you good pressure numbers? In the 2.0TFSI the oil pump's balance shaft can become worn and loose and create an internal leak, but it's pretty obvious as it can be wiggled around. Just check nothing mechanical feels loose in the pump and there's no major scratching in the pump mechanism and it should be fine.

Rod bearings are worth replacing if they're obviously knocking, which is much louder on decel. Does your knocking get louder on decel? And they're also worth replacing if the engine has a history of low oil pressure, just for safety. I replaced my rod bearings as I got low oil pressure and there was evidence the previous owner did too. I replaced mine without taking the head off, by just pushing the pistons up from the bottom.

[Von]

The tapping is only audible when revving the engine up to 2k rpm, you dont hear it on deccel. I managed to replace the oil pump and rod bearings, noise isnt gone, and another problem popped up, the car starts perfectly fine the first time, then, if you shut it off, it wont start for a minute or so, after which it will start again, any idea whats causing that?

[ZoliWorks]

Also, genuine question, since my turbo is pretty much done for, would a bigger turbo be an easy upgrade, or am i gonna have to replace injectors and so on?

As someone who's done it on the 1.4 122hp CAXA, I'd advise against it. I've installed the turbocharger off of a CAVD (160hp), no cat downpipe, full 63mm exhaust, front mount intercooler kit, watercooled-intercooler block-off, r8 coils mod, ngk 1 step colder plugs and probably a few minor things I'm forgetting. The car was able to achieve 240hp on 100 octane and a little over 320nm torque.

It's fun for a while but you get bored of it fast. If you want fun, the 1.4 is not it. There's no replacement for displacement. You'll be spending upwards of 6k to make your car go faster than a stock GTI, who then can get a remap for $400 and beat you anyway. It's a small engine with a lack of low-down power.

Plus, you, on the BLG, should be able to just get a remap and get 200-210hp, so is it really worth investing all that money for 30 extra? Get a GTI, you wont regret it if you want fun, you will regret it if you want fuel economy..


TLDR: Fix your turbo rather than upgrade, not worth the investment.

[Von]

Cheers, safe to say a turbo upgrade is off the map.