Clunking / chugging sound when cold started (w/video)

[Volumetrik]

My Fiesta developed a weird sound on cold starts. It's hard to describe, so I posted a video below where you can really hear it well, especially the later part of the video where I open the door and record under the car. It goes away after a few minutes of idling. I can also confirm that after 20 mins of driving, parking and doing the exact same small revs don't reproduce the sound.

At the same time this sound was starting to develop, an exhaust leak where the flex-pipe on the catalytic converter popped up as well.

I changed the exhaust post catalytic converter with a used, but good condition one. I also just had the flex-pipe on my catalytic converter cut off and replaced at a local mechanic.

After all of this, the sound is still there on cold starts. The mechanic says is shaft end play on the turbo, which I doubt, but could be possible.

What do you guys think? I have not seen other sounds or reports like this on the forum yet, and I'm pretty stumped.

 

[Dialcaliper]

Have you checked for the noise with the engine bay open? I’d be curious if you can hear it there.

Just a question as the phone audio makes everything sound a bit odd - are you talking about the “snort/raspberry” noise right as you begin revving, or the kind of “warbling” sound it makes especially as it settles back to idle?

If it is indeed anything to do with the turbo you can experiment by unplugging the diverter valve and/or wastegate solenoid and see if the noise changes character on revving.

Are you sure it is noise out the exhaust? Can you hear it at all at the tailpipe?

 

[TyphoonFiST]

How many miles on the FiST? did you take off the inlet Hose on the compressor housing and inspect the Turbo for shaft play? This could also be the DMF starting to give up the ghost.

 

[Volumetrik]

Thanks for the replies. It's a 2014 with 140k KM's.

Yes, I'm talking about the snort/rasp sound when I begin to rev. I'd have to get someone else to stand at the back of the exhaust and tell me if they hear it. I'll report back on that soon. I'll try the two avenues @Dialcaliper mentioned, I'll report back as well.

Yes, next step is to physically inspect the shaft end play. Interesting comment about the Dual Mass Flywheel possibility @TyphoonFiST . How would I check that? I'd have to pull the trans and inspect it physically, or there is another way?

 

[foodtruck]

This is what my DMF sounded like just before I replaced it

View: https://www.youtube.com/watch?v=LdOWn6CEieU

 

[Volumetrik]

Sounds pretty similar to yours. The only thing I want to rule out is that there is no remaining exhaust leak. I'll inspect all the connection points from the manifold to the catback.

 

[Volumetrik]

Here is a new video from an overnight cold start. The noise is different and somehow even worse.

This sounds to me like an exhaust leak, what would you guys say? My phone crashed and cut the recording short, but the extra ringing sound disappears after a while.

When I get back from my road trip, I'll take time to inspect the turbo manifold connection points and see if any studs have loosened over time.

 

[Volumetrik]

To follow-up on this, I'm confident I have found it the problem.

TL;DR : Broken stud between the block and the exhaust manifold.


Overall picture with context.


Closeup of the broken stud.

Since the stud looks to be broken after the center portion of the stud, my chances could be a bit higher since no torque is still applied on it.

I'll have to order a new oil feed tube it seems...

Symptoms from the service manual seem to indicate this as well.


I'll follow up in a couple of weeks when I receive the parts and perform "the extraction".