Strange Exhaust Noise

[ncslee]

Hi

Been using the car more frequently recently, it's developed what I can only describe as a rattle/popping noise from midway under the car.
It sounds almost as if the exhaust is blowing & rattling the heat shield. However it only happens on overrun & not whilst accelerating.

Anybody have any thoughts on this?

Will take into work later in the week to get it over the pit & have a good look.

Thanks Lee

 

[BennyD]

Easy, rip off the standard resonator and get yourself an X/H pipe fitted. That way it'll make more noise and you won't be able to hear the rattle! You'll thank me if you do.

 

[ncslee]

If it is the centre box thats blowing then it will be coming off for an x pipe.

I'm more worried that it's one of the cat's thats disintegrating.

Just seems strange it's only on overrun.

Lee

 

[BennyD]

Give the cat canisters a thump with a wooden hammer handle and any cat issues will be immediately apparent.

 

[ncslee]

Ok thanks Benny will try that when i get it over the pit later in the week

Lee

 

[Felonious Crud]

Easy, rip off the standard resonator and get yourself an X/H pipe fitted. That way it'll make more noise and you won't be able to hear the rattle! You'll thank me if you do.

Benny's right. In fact, his suggestion solves a multitude of problems. I can no longer hear the speed warning sensor, shite music on the radio or Mrs. N.

 

[CatmanV2]

Or it could just *be* the overrun?

However, I must concur with my learned colleagues above that an x-pipe is the only sensible solution.

C

 

[2b1ask1]

Its the car telling you it wants to let you have crackles and pops from an X-Pipe.... Go for it!

 

[Parisien]

Rattling?.......heat shield an issue ....also if like pebbles in a tin from underneath, its your CAT breaking up, get it checked out rather than running it


P

 

[midlifecrisis]

If a cat is breaking up its normally accompanied by a CEL as the lambda sensors detect different temperatures. That's what I got, best is to remove the exhaust section after the manifold downsides and have a look in.

 

[gingeh721]

Snap. I've had an increasing number of P0421 codes which are now accompanied by P0431 codes. My problem is not the mid section as it's now fitted with an x-pipe.

On overrun, above about 3.5/4k, the exhaust sounds like you describe. A tinny and sort of hissing ttttttttssssssscccccccchhhhhhhh sound.

The car has 4 x brand spanking new Bosch lambdas and just had a dealer 4yr service where I was told the car is in excellent condition.

After quite a bit of research and reading other people's experiences I'm banking on the primary cats being knackered.

I plan to get the primaries gutted and secondaries replaced with 200 cell sports cats at prospeed in Cardiff.

2.5k for Larini cats is crazy expensive, replacement OEM cats is pointless as it'll happen again, so I think custom is the way to go.

There are however second hand Larini cats for 4200/ GS euro style headers on eBay at the moment for 1500 quid. I still can't justify that amount for cats though.

Gingeh721.

 

[Chrisbassett]

Get Charlie to replace your x-pipe too, gingeh! Burble, burble, pop pop pop!

 

[gingeh721]

Chris,

Will be speaking to Charlie very soon. I was secretly hoping the primary cats would fail to be honest. It was just an excuse to get the extra sounds and still being able to tell my other half.

 

[ncslee]

Update

After investigation have removed the front section from the off side exhaust. primary cat in several pieces so removed. refitted pipe & still the same noise.

Removed the pipe & restared without noise stopped.

Engine sounded great with no exhaust!!!!

You couldn't hear any rattling when you shook or knocked the pipe around after removal.

Have knocked out the secondary cat which is in 2 segements/slices both about 80mm thick. pipe refitted Noise cured.

No CEL at the moment

Spoke to Greg (breakeronly) £660 for a replacement cat.

Still undecided whether to fit a replacement or whether to knock the cats out of the other side to match.

Had the emmisions checked & It will pass MOT as is.

Your thoughts please.

Lee

 

[BennyD]

Remove the other cat. IIRC, those cats are 600 cell and are largely superfluous. You will get better gas flow, more sound and it will still pass emissions. If you then install 200 cell cats in place of the 400 cell cats and an X/H pipe, happy days!

 

[mjheathcote]

If I understand your post correctly you have knocked out your primary and secondary cats and it passes the emissions test? How so?

 

[CatmanV2]

Sounds like he's knocked both primary and secondary from one side....

Given the 4200 exhaust, isn't it the case that the emissions test only measures one cylinder bank? I've never seen a tester probe more than one tail pipe in a multipipe setup.

C

 

[ncslee]

Catman you are correct I've taken primary and secondary out of one side only, had emission checked by the friendly garage that carried out the MOT a couple of months ago. They checked both sides of exhaust & readings on the machine showed it would still pass the Mot! They are obviously higher than before but still within allowed limits.
I was more interested in what effect it might have on the engine management if I remove the cats from the other side.

Lee

 

[CatmanV2]

Catman you are correct I've taken primary and secondary out of one side only, had emission checked by the friendly garage that carried out the MOT a couple of months ago. They checked both sides of exhaust & readings on the machine showed it would still pass the Mot! They are obviously higher than before but still within allowed limits.
I was more interested in what effect it might have on the engine management if I remove the cats from the other side.

Lee

Interesting. I thought that the 4200 exhaust was effectively one pipe per bank. Do you have an X or H pipe? Otherwise I'd expect the non catted side to fail. Still.
Equally I'd expect it to throw CEL and fail if you take them all out. It might take a while though I guess for the trims to go out enough? Or I could be talking ****.

C

 

[BennyD]

It might be that the exhaust gasses meeting and mixing at the X in the standard resonator is diluting the 'uncleaned' gas with 'cleaned' gas. The reading will be higher but is obviously still within limits. It may well be detrimental to the engine in the long term to have different restrictions (cats) in the exhaust between cylinder banks.