Rather worrying new noises

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Sp!ke

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Driving home last night I thought the car sounded a bit rough.

Nearing home the noise seemed to get worse. A sort of nasty mechanical resonance at medium to high revs and on the overrun.

I havn't had the chance to have a proper poke around the car and I whilst I suppose the noises could be caused by something as simple as an exhaust hanger coming adrift or something, it really doesn't sound good and I have a hunch that it might be something more serious like a camshaft or maybe even big end rumble. If it is something serious, it would signal the end of my W124 as I'm not prepared to throw much money at it outside normal maintenance jobs now.

I'm also not quite ready (savings wise) for its replacement (hopefully a R129) either so I do hope that I am mistaken and the noises aren't the cars final death rolls. :(
 
Fingers crossed Sp!ke, that it's nothing expensive.
 
has it got cats?

They can make a horrible noise if they start to break up

Good suggestion, it may well be the cats, they are 18 years old afterall. I'll get underneath and have a proper listen.

I suppose on a 1991 car I could just cut them out and replace with straight pipework assuming that its emmissions are still ok.
 
Does it vary with engine revs? Could be timing chain/tensioner/guides Do the long screwdriver test--place business end on suspect part of engine--place ear on handle--- taking care not to get caught in any moving parts---has a stethoscope effect to help localise origin of mechanical noise
 
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I suppose on a 1991 car I could just cut them out and replace with straight pipework assuming that its emmissions are still ok.

I did a quick Google and it seems that cars registered before 1/8/92 do not need a CAT for the MoT emissions test :)
 
Does it vary with engine revs? Could be timing chain/tensioner/guides Do the long screwdriver test--place business end on suspect part of engine--place ear on handle--- taking care not to get caught in any moving parts---has a stethoscope effect to help localise origin of mechanical noise

I don't think (still unsure) the noise changes with engine revs other than the fact it occurs above 2.5k rpm. If I am right and it isn't connected to rpm then that would be good news as it would suggest its a resonance rather than a mechanical component making the noise.


I did a quick Google and it seems that cars registered before 1/8/92 do not need a CAT for the MoT emissions test :)

Actually I understood that the law is even less precise. If any car can pass its emissions test without a CAT it wont be failed on its MOT regardless of age. The difficulty lies with the test getting more and more stringent the newer the car making in increasing harder or often impossible to achieve without a cat on newer models.
 
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Post 1 jan 1992, cars must produce no more than 0.3% Carbon monoxide (CO) at idle, with a maximum unburnt hydrocarbons (HC) figure of no more than 200 parts per million (PPM).

1983-1991 limits are 3.0% and 1200 PPM and 1973 - 1982 it's 4.5% and 1200 PPM. Pre 1973 is just "no visible smoke at idle".

In order to achieve 0.3% CO, most cars will require a catalytic convertor hence the nickname "cat test". It's not strictly a cat test because very often it's a faulty coolant temperature sensor or ignition problem that causes a fail. Often it's blamed on the cat when that item is still in good order.

No car is required to meet tougher standards than those applicable when it was type approved (some Rover 820 turbos get an exemption) and kit cars just need the "smoke test". The cutoffs for age are determined by the ELDER of the chassis of the engine. Therefore, a 2009 car with a 1990 engine gets tested as a 1990. A 1990 car with a 2009 engine also gets tested as a 1990.
 
I don't think (still unsure) the noise changes with engine revs other than the fact it occurs above 2.5k rpm. If I am right and it isn't connected to rpm then that would be good news as it would suggest its a resonance rather than a mechanical component making the noise.

More than likely that would be correct.:thumb:
 
Post 1 jan 1992, cars must produce no more than 0.3% Carbon monoxide (CO) at idle, with a maximum unburnt hydrocarbons (HC) figure of no more than 200 parts per million (PPM).

1983-1991 limits are 3.0% and 1200 PPM and 1973 - 1982 it's 4.5% and 1200 PPM. Pre 1973 is just "no visible smoke at idle".

In order to achieve 0.3% CO, most cars will require a catalytic convertor hence the nickname "cat test". It's not strictly a cat test because very often it's a faulty coolant temperature sensor or ignition problem that causes a fail. Often it's blamed on the cat when that item is still in good order.

No car is required to meet tougher standards than those applicable when it was type approved (some Rover 820 turbos get an exemption) and kit cars just need the "smoke test". The cutoffs for age are determined by the ELDER of the chassis of the engine. Therefore, a 2009 car with a 1990 engine gets tested as a 1990. A 1990 car with a 2009 engine also gets tested as a 1990.

whilst these co limits are probably correct, it should be noted that a lambda value is also stipulated for the post jan 1992 cars. the purpose of this is to prevent anyone simply weakening the mixture to pass the test. the pass values are between 0.970 and 1.030%. if one did weaken the mixture on a post 01/92 car with a missing cat the value would be above 1.030%, ie excess air.

no idea what that rattle is though :dk:
 
Engine mounts ?
 
I had a closer listen to is this evening but still cant really pin it down.

Sat in the car its uncomfortably loud and nasty, a sort of metallic rattly grating noise with the sound appearing to come from insde the dash.

Standing by the engine bay revving it, I couldn't really make out the noise at all. :dk: Sitting in the drivers seat, foot on the gas with the door open and my head down by the sill, it might be that the sound is coming from under the car - not sure.

I need to get it on a ramp with a helper I think.

At least it is beginning to point to something non engine related.
 
Good news then.

Heat shield round the exhaust ? I've had this on another brand. Rattly, tinny noise.
 
v belt tensioner assembly?
 
heatshield behind the downpipe attached to the bulk head are notorious for rattling
 
Thanks, Ian, I'll put it on my check list. I did notice that heat shield was particularly close to the downpipe actually.

Interestingly, I only get the rattle after 15 minutes or more of driving when the engine is fully hot.
 
i'd also go with the heatshield theory here if it does it at standstill. you may be able to see /hear it from crawling/looking under the car whilst an assistant revs it. use something to poke the shield/exhaust to see if this fixes the issue as you go, then just bend the shield to a good shape to avoid hitting anything.

also make sure the screws that hold the sheild on are still attached. a couple of mine came loose and rattled against my towbar until i remounted them.
 
I spent three hours trying to track this down today with the car on the ramp and without success.

Inside the car, the noise is very pronounced. Outside the car, even underneath the car, its very faint if at all noticeable. The noise doesn’t seem to be in time with the engine revs (indicating resonance maybe) but the noise starts at 2.5k rpm, only when the engine has been run for a while like after a motorway run. Sounds a little like a worn bearing but it’s not directly engine speed related.

So I got the car really hot so it was making the noise continually and then did a quick engine oil change to see if the thicker cooler oil would quieten the noise - and it didn’t. (I thought this suggested the problem as being non engine related)

Then the serpentine belt was removed to rule out alternator, water pump and other possibly ancillary noise and the noise was still present.

Then to rule out cam chain slack we manually put tension on the tensioner, over tightened the chain and the noise still remained.

None of the exhaust shields seem to be vibrating, the cats seem solid and quiet. In fact it’s really hard to hear the noise at all under the car, let alone pinpoint it.

So I'm still thinking is likely to be a resonance issue or something other than mechanical. Something that would sound louder inside the car than out.

Maybe something on the fuel circuit? The fuel pump seems quiet enough but I guess there's no harm in changing the fuel filter. There is a clicking noise coming from the inner offside wing (regenerative valve maybe?) Could this be causing the noise?

Off to buy a mechanics stethoscope in the hope that it'll help but really running out of ideas now.
 
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How about the bracket supporting the downpipes that bolts to the gearbox area? It's metal-on-metal there with the pipes supported on a metal clamp.

They can be a swine when they rattle as the pitch/frequency changes with heat and engine RPM.

Definately worth a look. How old are your engine mounts BTW?

Will
 

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