Possible Bad Catalytic Converter?

[goldstar]

I start my engine and when it bursts into song I get a rattle under the passenger compartment - more pronounced when I rev it than under cruise or idle. Everything else is normal and no change in performance. Bad converter? What do you think.

Happy Motoring!

[jay]

Could be that, could be a rattling undertray, could be muffler banging on the coachwork cuz a mount is loose, prolly not bad converter if there's no change in how it goes. Easy to diagnose, once you get the car up and crawl underneath it.

[goldstar]

Thank you.

I haven't had a chance to go under the car yet but when I do I'll follow your suggestions. I was just looking for a quick answer to narrow my search. From what I can judge topside, the muffler seems securely mounted though.

Happy Motoring!

[jay]

I know cats can fail by leaving chunks of their innards banging around in the case. But when mine went, it just clogged up. Either failure mode is likely to increase backpressure enough to notice a power loss, specially if you are running forced induction..

[viper_707]

i bet u its a heatshield, theres a reason why i dont have any on my car anymore

[Ace]

yeah, there's no deffinate answer till you get under there and look. just go under there and start moving things on the exhaust and see what rattles. tap the converter and see if you can hear loose material inside.

[irishkev90]

Loose heat shield was my problem as well. Hose clamped it in place at first, then just tore it off completely. Problem solved.

[D323]

Heatshield is the most common cause of that as it is only tack welded in a few spots from the factory. Any reputable muffler shop should be able to re-weld the shields back on as needed (probably better than the factory by using a longer bead). At first I thought about your setup where you have the Racing Beat muffler and thought that there was no cat heat shield to speak of, but after some digging I found you still have the factory cat infront of the racing beat system correct?



If the shield is secure and you suspect the catalytic converter there are plenty of high-flow cats aftermarket as an option to help optimize exhaust flow.

Good luck.

[goldstar]

Thanks, Donnie. Yes, I still have the factory cat in front of the RB system. This weekend, I'll go underneath and check things out. I hope it's not the cat to save some money. However, should I need a new cat, what would be a good, reliable aftermarket high flow type to consider?

Happy Motoring!

[D323]

Mike;

I would think that a brand like Magnaflow or Flowmaster would be your best bet as both offer a higher flowing converter. I have not had much personal experience with either so I cannot fully endorse them myself. Perhaps another member has one that would like to chime in? Magnaflow only offers a cat for the 2.0L, here, that is a bolt in replacement. My memory is fuzzy but you have the 1.8L correct? I would presume that the exhaust systems are not different between the 1.8L and the 2.0L but I do not know for sure. The nice thing about the Magnaflow website is they offer both an OEM grade replacement as well as an upgraded better flowing model. Flowmaster's website offers only universal ones for other Mazda models with similar exhaust systems. Their product remind of the universal cat replacements that you see on eBay and other websites that have to be welded on.

[goldstar]

Thanks for the information, Donnie. I have the 2.0 L and should I need a new cat I'll look at the Magnaflow.

Happy Motoring!

[goldstar]

I went underneath and everything seems secure. The heat shield is secure and so is the exhaust system. The rattle is most pronounced when I rev the engine but not so much, or not present, at cruise, and there is no noticeable performance decrement. Is there a definitive test for a bad cat before I spring for a new one? I assume it's the 2nd cat, not the 1st, since that's where the noise seems to be coming from.

Happy Motoring!

[goldstar]

Update

I spoke to a tech friend of mine. He told me to beat the cat with a rubber mallet, and listen. I did - nice crescendo of sound. So cat 2 is bad. Taking Donnie's advice, I ordered a Magnaflow free-flow, 49-state, direct fit, OEM grade cat. OEM grade is more expensive than standard but nothing is too good for the penultimate driving machine. I ordered it from Exhaust4Less.com at a cost of: US $338.05; shipping is free and no state theft.

Since I already have the RB exhaust, the free-flow cat should give me even more power. Gollee, I hope so.

Happy Motoring!

[goldstar]

According to tracking, the new Magnaflow cat will be delivered to my home on Monday, July 9th. If the good Lord's willing and the creek don't rise (or it doesn't rain), I'll install it on Tuesday. I'm going to need new gaskets since they're not included so it's off to Mazda tomorrow for their acquisition.

Happy Motoring!

[jay]

Whell naow there's yer problem!