Help! Unusual noises/backfire whilst accelerating

R

ReturnoftheMatt

New member
Over the last month my P380 has developed some odd noises under heavy acceleration between 3-5k rpm.

There are no fault codes being thrown, no unusual idle or irregular sounds from the engine at any other time. I thought initially it could be spark plug or injector related, but having connected to a diagnostic, nothing unusual was showing. Fuel/Air ratio was normal, suggesting that injectors are working fine and there's no air issues going into the engine?

So we filmed this video (link below) yesterday, which makes me think the noise is coming from the exhaust system rather than engine... Could it be the cats? The car definitely has issues with sticky exhaust valves, but I don't think that would cause this issue as the exhaust pressure by that point surely wouldn't cause the backfire/stutter on the revs? It also does this noise in all modes valves open and closed. Perhaps there's an exhaust leak higher up the system? Though you might expect a sensor to throw up a code for that? It's also much worse when the exhaust/cats are colder (engine at temperature before any hard pulls are done, don't worry!)

I'm hoping someone out there has either experienced a similar issue or has any idea what might be causing the noise?

Thanks

Hopefully the link below works but shout if not and I'll try a YouTube upload instead!

https://photos.app.goo.gl/dworEWos65BZPDLy6
 
Mmm, that does sound unusual. I agree with your initial thoughts. IMO, noises like this would normally be caused by unburnt fuel in the exhaust. It might be worthwhile pulling the spark plugs to examine their colour. This might show if anything is running rich or even narrow it down to a particular cylinder/injector.
 
Very odd. Sounds like a misfire, pop bang overrun noise.

Related to your previous post? - https://www.ftypeforums.co.uk/viewtopic.php?p=70831#p70831
 
Thanks both. Still at a loss to what is causing this although it seems to have coincided with significantly worse rattling coming from the exhaust valves. I'm 99% sure it's not related to my previous post. That seems to be a fairly common noise coming from the belts when the engine is cold/belts have moisture on them.

I think I might start with fixing/deleting the exhaust valves, as that's a job that needs doing anyway. If that doesn't fix it, we'll look at plugs and injectors.
 
Latest on this - exhaust repaired by Mod Stock (they do an excellent job, Chris and the team are awesome) but still pops under acceleration. We've ran live diagnostic data under load and nothing seems unusual that would indicate spark plug or injector issues. No fault codes at all relating to the issue. We also checked the spark plugs which look normal - they were last changed in October 24.

The only odd reading we were getting from the live diagnostic were related to the post-cat o2 sensors, which seemed to be intermittently showing no readings at all. You would have thought a fault like this would throw an engine light or something?

We don't really know what to think of next, so I think it will be a case of booking it in to Tom Lenthall and hope their experience prevails!
 
I’m sure Tom and his team will be able to get to the bottom of this.

I wonder if it could be a partially collapse cat, cracked flange, or similar.

Hopefully it’s a quick and not too expensive fix - be good to hear what it turns out to be.
 
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