Cat Noise?



Cat Noise?

Postby bytor » September 3rd, 2014, 8:50 pm

Have a pesky tick that I started noticing when the engine was at operation temperature. It’s more of a ping or tinny sound than a nock and it doesn’t seem to be at a valve train frequency. When the engine is first started, it’s quiet with nothing but the fuel injectors ticking away. But as it warms you begin to hear a faint tick that gets louder as it warms up. Went through all the upper engine usual suspects with a stethoscope, valves, distributor, belt driven accessories and could not find the noise. Started wondering about the flex plate cracks or loose torque converter bolts so got the car up on ramps and got busy with the stethoscope on the under side. Oil pan, flywheel cover, transmission and fuel filter/lines all quiet. While laying there scratching my head, I remembered having the same type of racket on a 2005 Pontiac G6. It was the catalytic converter. So, put the stethoscope on the passenger side pre cat and cat, no noise. Moved over to the driver side pre cat and “BINGO” it was ticking away. I’m going to double check but I’m confident its the source of the noise. Any of you C4 vette guys experienced this problem?

Now I need to research what my options are for replacing the front Y pipe. With or without pre cats? Wonder what state my main catalytic converter is in. I did a back pressure check a month or so ago and I have no back pressure issues.

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Re: Cat Noise?

Postby 87vette81big » September 3rd, 2014, 9:00 pm

If you must Pass Emission smog tests Bytor its best to replace with OEM Parts.
Or Aftermarket Equivalents .
Grumpy will want to install long tube headers & all new exhaust back.
Its a Corvette so parts are 2-3 times higher than normal.

Many used to eliminate the Precats on the 1986-91 TPI C4 vettes.
Or install true dual exhaust.
Resonance is a #1 complaint on high flow systems.

Research carefully what fits your needs & budget best.

The original GM Cats cleaned the exhaust best.
Unaffordable to purchase new if you find NOS by chance.
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Re: Cat Noise?

Postby bytor » September 4th, 2014, 7:22 am

87vette81big wrote:If you must Pass Emission smog tests Bytor its best to replace with OEM Parts.
Or Aftermarket Equivalents .


No emission testing here in SC. Looking around it would seem most of the aftermarket replacement Y pipes are crush bent like stock or even worse wrinkle bent.

Magnaflow has a nice setup that appears to be mandrel bent. http://www.magnaflow.com/02product/shopexd.asp?zone=main&id=1122 I will give them a call to get more info.

I would like to keep things stock as much as possible so I will look around on the OEM NOS market as well.
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Re: Cat Noise?

Postby grumpyvette » September 4th, 2014, 9:28 am

this is one more in an ENDLESS LIST of reasons EVERYONE who is into this automotive performance hobby NEEDS a decent MIG or TIG welder and NEEDS to have the skill to use it!
chances are excellent that the cats core has fractured or melted and its loose crap internals bouncing back and forth with the exhaust flow,is causing the noise and more than likely a power loss , a leaking fuel injector or a defective oxygen sensor, or excessive use of injector cleaner spray or some fuel additives in the fuel, can cause a catalytic converter to melt internally or plug up.
this defective cat is very common on older c4 corvettes
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viewtopic.php?f=56&t=3049&p=8053&hilit=catalytic#p8053

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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Cat Noise?

Postby bytor » September 4th, 2014, 12:42 pm

Got some info back from Magnaflow on their Y pipe. I was wondering why it was listed as 'off-road' and it's because the pre-cats are weaker than stock I guess like 87vette81big said.
87vette81big wrote:The original GM Cats cleaned the exhaust best.


Response from Magnaflow answering my questions on converter type, pipe size and mandrel bent or not.
"It will have 2 converters on the system with the ceramic bricks. The part is off road use only though so it won’t have a strong enough wash coat on the internal bricks to pass a sniffer emissions test if your state has that kind of testing.

The part has all 2.5” piping, until after the y pipe, it will have 3” piping. The whole system has mandrel bent piping."
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Re: Cat Noise?

Postby 87vette81big » September 4th, 2014, 1:25 pm

Sounds like a Winner the Magna Flow Bytor.
I am outside of Chicago area.
No SMOG testing here too.
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Re: Cat Noise?

Postby philly » September 4th, 2014, 10:13 pm

just gutted the cats on a c5 a couple weeks ago for that very problem that grumpy posted a great picture of. was making a very weird clunky sound as the exhaust gasses shuffled a chunk of the material around in there. before dismantling i put the car on a lift and verified with a stethescope, after gutting the cats with a hammer and a big flat tip screwdriver, noise is gone.
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