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Catalytic convertors

michelinman

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This is another ongoing question to find this bloody annoying sound in my 2010 SV6 SIDI, hence the question yesterday on extracters and convertors.Ive lost count how many times my car has been in the dealers looking for this light knocking. The trans and torque convertor have been checked ok but the noise is still there even under very light throttle. It comes in at about 1600 rpm and continues up to 2000 rpm and as the engine gets hotter the rev range climbs by 200 to 300 revs and is a little quieter. Now a retired mechanic friend has suggested that it may be the catalytic convertors. I have read heaps of data on them like how they can effect fuel economy and break down and rattle while driving. My fuel economy isnt that good from what Ive read that it should be. Has anyone got the same problem out there? I would like to find out. Thanks.
 

anarklov3r

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A knocking sound can also be an exhaust leak in your system (often caused when a new exhaust is fitted, or scraping on a high speed bump accidentally). On my old VN, i have no idea how, but almost half the manifold bolts fell off causing the engine to sound like it had thrown a bearing and lifters were ####ed. Accelerating made it worse, and was just like a loud tick / bang over and over while you accelerated.

On my WM caprice now, my cat back exhaust doesnt quite mate with the HSV extractors and cats properly (different flange type) and i've got a small leak that at low revs sounds like knocking. Easy to check for, either use your ears and put your head under the car while somebody lightly revs it, or if you have a smoke / fog machine and a garage (even a smoke will do) blow smoke onto exhaust joints and check for air blowing it around. You can find a few videos on youtube by searching "exhaust leak check with smoke" or something like that.
 

michelinman

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Thanks for that. I think the last time in the dealers some new exhausts were fitted but not the cats. I have more checks to make but thanks again.
 

Kiddo

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Do the exhausts on the SV6 have some sort of heat shielding?
 

michelinman

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Just an update on the so called inherent noise. I contacted Holden NZ by e-mail and recieved a reply from Holden Aust after
explaining the noise that I hear that it is a characteristic of the SIDI engine, but nobody can tell me what it is. My engine block has been replaced after 30k for whatever reason but the sound is still there. I have reason to believe that the torque convertors are the same as used on the
FG and Explorer Fords and have some warranty issues, maybe we will have a good listen to this area. Anyone have any ideas or suggestions
other than rendering the whole exercise as scrap!
 
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