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.
Check to make sure that the modifications from removing the rear muffler has not accidentally pushed the whole exhaust piping forward slightly as this could lead to a support bracket on the exhaust touch and resonate on the front cross member.
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.
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.
It still sounds (excuse the pun) like something from the exhaust is touching a body part somewhere.
Make sure you examine and feel all along the whole exhaust system (when cold) to make sure it is free of everything except rubber hangers.
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.
Just a though. Check the EGR pipe. The EGR valve is on the rear of the engine, then the connecting pipe runs round to the front. The pipe is wafer thin.
My diesel 08' T31 has a noticeable sound under light acceleration , a bit like an open air box noise but goes when accelerating more .Unlike any car I have driven before .I am not sure if they all sound like it OR do I need to investigate as well :?:
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.
The sound hasn't gotten any worse, and I've kind of become used to it by now.
Weather too cold for getting underneath car.
I'll just leave it until warmer weather then have another look for exhaust touching sub frame or something else.
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.
Could your flexible exhaust joint possibly be internally corroded and need replacing ?
Happened to me once where exhaust sound was louder in the cabin. Thought it was a leak but exhaust place said flexible joint was bad and replaced it. Much better afterwards.
That's another thing I could consider. Visually though it looks fine. But I have gotten used to it now, its really not that bad. Will keep that in mind if it ever gets worse.
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