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Strange engine sound - Can you help diagnose it?

JackB

Active Member
Jan 18, 2020
97
56
Hi All,

My Cupra 290 (2018) has just started making a strange engine sound, and i'm wondering if anyone can help diagnose it.

Recent changes to the car which could be a factor:
  • Full turbo back valved exhaust with 100 cell cat.
  • New spark plugs
  • Stage 2 engine and DSG remap
Full details of mods are on my readers ride thread (link in signature). I will also be contacting the guys that installed the exhaust and the engine tuner for advice on this.

This sound did not occur in the first c.200 miles following these mods, but then just appeared out of nowhere. It didnt build up gradually, just appeared.

This has occured on two different days now - between the first (a few days ago) and second drive (today), I checked under the engine bay for anything obviously loose, and also all of my fluid levels - nothing of concern to note.

On the second drive, I used the torque pro phone app to log my temps, air fuel ratios, boost - and any other paramaters I thought might be relevant. Nothing of concern to note here even when the sound was happening.

Additionally, I have found one engine fault code when scanning with Carista (15048) - I can't find any details for this online. There are no warning lights on the dashboard.

1595760593599.png

The sound usually occurs at high load and high RPM, but sometimes it doesnt (i'd say it does about 80% of the time). It also sometimes occurs at lower RPM, particularly if accelerating hard in lower gears (less than 25% of the time).

Rather than try to describe the sound, I've linked two dash cam clips - the soundaktor is off so that won't interfere. The mic is on the camera itself, windows were up (the sound is actually much harder to pick out with the windows down). You should be able to pick it up as the tone just switches instantly to one that is more coarse.


The only other thing I have seen the car do which may be linked is let a cloud of smoke out of the exhaust after letting off after accelerating hard. This has only happened twice to my knowledge, and interestingly, not after a pull where this sound occured. Here is a clip anyway in case it is relevant:


Any thoughts?
 

martin j.

Active Member
Feb 11, 2007
1,159
369
Fife
The engine sounds similar to my Honda in vtec, could this be the exhaust carbon in up, do you have an induction kit? the two combined may just be sounding different to what you were used to? The smoke however looks blue, so oil smoke? Checked the oil level lately, is it using oil or been overfilled maybe.
 

JackB

Active Member
Jan 18, 2020
97
56
The engine sounds similar to my Honda in vtec, could this be the exhaust carbon in up, do you have an induction kit? the two combined may just be sounding different to what you were used to? The smoke however looks blue, so oil smoke? Checked the oil level lately, is it using oil or been overfilled maybe.
haha you're not the first person to say that about VTEC! It does doesnt it.

It's definitely a dodgy sound rather than just been different to what ive been used to, it sounds worse IRL than it does in the video. I do have an intake too, but thats been on for months.

I checked the oil after the first time I noticed the noise and it was just under half way between min and max, I topped it up to be about 3-4mm below the max after that. It wasn't burning oil with any significance before the tune, not enough miles since to be sure. Hopefully the smoke is just a one off and not actually related to this noise, I think after posting in the MK3 facebook group too, that its more likely to be a vibration than anything else.
 

martin j.

Active Member
Feb 11, 2007
1,159
369
Fife
I changed a centre pipe on one my Ctr’s, the exhaust note changed dramatically and when driving really wet conditions it sounded like all hell was breaking loose under the car, it seems the water was hitting the hot exhaust and boiling off creating all manner of noise, and vibrations under the front seat area.
 
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Legojon

I only wanted a remap
Staff member
Moderator
Jul 7, 2015
5,083
2,574
Is it dependent on revs? Eg the valve opening on the exhaust. Sounds like summats rattling ... maybe movement in the exhaust?
 
Jul 3, 2020
16
1
Kent
Sounds like a vibration/rattle to me. Seems to die off with exhaust resonance if that makes sense.


Sent from my iPhone using Tapatalk
 

JackB

Active Member
Jan 18, 2020
97
56
Thanks for the comments guys, I can now confirm it was the lid on the airbox vibrating (aftermarket MST).

Noise resolved using a bit of plastic to tighten the gap between the lid and the sides.

As for the smoke, I've been advised that it could just be stuff burning off in the new exhaust system, and not to worry unless it recurs, which makes sense to me.
 
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