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M9R Exhaust Blowout Sound Behind Engine

4K views 13 replies 6 participants last post by  Adrian4X4 
#1 ·
Car 12 years old / 110K miles

All exhaust system parts were original but in September I had to change my rear box / muffler due to a large blowout.
(Original part is a single piece including long mid pipe section, whereas aftermarket rear box is separate. You are required to cut original pipe and join rear box with a suitable clamp.) I did this successfully. Not that difficult other than having to cut slots at the end of the original pipe to achieve fit inside the flared pipe of the new part).

I am aware that a new rear box / muffler significantly changes the sound of a car, however I am now hearing a much increased exhaust sound from the front of the car, most audible from inside or from bulkhead area when bonnet is open.

All visible exhaust parts underneath are in good order and towards front, as far as can be seen, no obvious corrosion is visible. However I would need to put car on a ramp and take off plastic engine protection tray underneath to investigate higher up towards exhaust manifold and turbo area.

Has anyone had this experience, or know what could be blowing out in the area I have described, ie behind the engine?

Turbo appears to be working fine and fuel consumption remains unaffected, in fact, if anything I have seen an improvement since new exhaust fitted although that could be driving related.
 
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#4 ·
Today I raised the front of the car and removed the plastic underneath protection panel. I have scrutinised and photographed all forward sections of the exhaust and as far up as I can see, which is not that far. The forward pipes, forward muffler, curve up to engine bay, and all joins and flanges appear fine with virtually no corrosion. Visible flange bolts / nuts even look to be in good order. I can't feel any blowout air. I have virtually eliminated any problem underneath.

I observed that the blowout sound is not that loud from underneath. It is louder from above coming from rear of engine with bonnet open.

I then reached and looked down as far as possible behind the engine from under the bonnet, but the area is tight and I can only get my arm down so far.

I'm afraid that in order to investigate any further I would have to invest in one of those tiny cameras on the end of a flexible umbilical to see the hidden areas.

Revhead Kev

I didn't specifically check that but I did take a few photos of the area when I was underneath and will study them. You would be correct that indeed the whole exhaust is pushed forward a few mm after clamping on the new rear box. However I'm quite sure I do hear a blowout sound and as I said I think I can smell fumes in there.

I wonder if MOT would fail a car for a slight unseen blowout in a hidden area? They would not be able in an MOT to prove what it was.
 
#5 ·
I'm not any further on with this yet.
I bought an Endoscope camera, but not that great a picture unless held very steady. I'll need to work more at this to get a clear idea of whats going on in the hidden area behind my engine.
On idle, there's quite a bit of noise / resonance sound inside the car coming from in front. Its not that audible outside the car.
In fact the whole exhaust system sounds weird inside the car since rear box was replaced.
 
#7 ·
Yes, that's certainly a possibility because as far as I can see, the whole exhaust system at the forward end is in very good condition with no visible corrosion or cracks. When I have the chance to get car on ramp again, I'll scrutinise it again as you have said.
 
#10 ·
Adrian4X4 said:
I'm not any further on with this yet.
I bought an Endoscope camera, but not that great a picture unless held very steady. I'll need to work more at this to get a clear idea of whats going on in the hidden area behind my engine.
On idle, there's quite a bit of noise / resonance sound inside the car coming from in front. Its not that audible outside the car.
In fact the whole exhaust system sounds weird inside the car since rear box was replaced.
Don't forget that a resonance from underneath the rear of the car may also be enhanced towards the front on the inside.

The crazy world of acoustics! :headbang:
 
#12 ·
Update: In better weather I checked the exhaust system again thoroughly. I don't see any blowout or exhaust touching subframe or any other part of car. The change in sound is clearly the new exhaust back box / silencer, not a nice sound at all compared to the original, but then again it is an after market motor factor exhaust, not Nissan. Kind of wish I had repaired the small piece of rust on the original rear silencer and kept it on the car a while longer. Anyway I've gotten used to it now.
 
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