cat rasp/rattle driving me mad! - Alfa Romeo Forum
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(Post Link) post #1 of 8 Old 31-08-09 Thread Starter
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cat rasp/rattle driving me mad!

Help! I am at my wits end. Since replacing both cats of my 156 (cf3) as both had broken up (possible missfirefrom washing engine off - don't drive with a missfire) and both front lambda sensors (gone) I had had this rasping rattle, but only when the engine is under load/acceleration.

Does not do it on idle or light throttle, or over-run when changing down, only when open throttle accelrating or high speed - under load in other words.

I have had the front cat replaced twice (it sounds like its coming from the flexi there - but that seems ok, no leaks) with type approved cat, first Timax then another type approved brand - though clearly made in the same factory). It is still there the same.

I have spent hours under the car, checking, tightening, removing and replacing the cat, re-sealing it. Nothing seems to make it better! It is not the cat bracket, thats fine. I am at a total loss

I have just ordered the check lambda (though Regal said that was ok) and new plugs just in case, as it seems linked to shoving fuel in (open throttle).

Could it be the coil packs? These had tiny hairline micro cracks in I sealed with super glue.

Please help - I am at the point of chucking in the alfa towel. I have spent nearly £1k recently on a car that's worth £1.5k!

Also fuel economy not that hot around town - good on a long cruise though.


Hold the rear end slide....don't run wide!

156 2.0TS Veloce Lthr (02/02), silver, black Momo, BMC filter,V6 intake, DS2500 Front-DS Perf Rear pads, Conti sportcontacts, OMP strut Brace .

Built in Italy, on the last Friday before (hic) Xmas........:-/
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Heat shield(s)?
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Heat shield ?????? or with some of the models... the flexi joint.
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Check all your exhaust brackets from the manifolds through to the centre section... i found a broken /rattling one that was driving me crazy.
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I had a rattling bracket. Only under load and at 2800rpm.

Turned out to be the one between front pipe and cat (CF2 model)
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(Post Link) post #6 of 8 Old 01-09-09 Thread Starter
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Thanks guys, but its not any heat shields or brackets, all checked throughly and all A1 ok.

Its a CF3.

Smaky you mention flexi joint? It does sound like it comes from there, but I cannot see anything, no obvious leaks or damage - and both cats with it were brand new - so I thought the sound must be travelling and just sounding like its from there as it just has the wire mesh to get through I guess?

Could it be something to do with the lambda/coils etc. would a bit of rich mixture cause fuel to burn in there and cause the noise?? I am at a loss.
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Hi Dupes,
Have you had the water pump and auxiliary belt tensioner/idlers checked? they can also rattle under load like a broken cat.
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(Post Link) post #8 of 8 Old 02-09-09 Thread Starter
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Thanks for the suggestion - checked but positive its not them. Its not a rattle as such, more a rasp/reverberation.
The noise is exhaust related - and appeared as soon as I replaced the front and second cat - old cats no noise, fit new cats, start engine and the noise was there.

Anyone got any ideas or more details on the flexi that Smaky mentioned - what might be the issue as it does sound like it eminates from there.

Or if the coils/lambda and fuel idea I had is a possible?

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