[rl968]

Anyone ever seen this? Blew off on me. The sensor itself seems in tact, but looks like maybe the weld has pulled away from the exhaust. Are these welded in?

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[Cloud9...68]

Yes, the O2 sensor bung is welded in place. The good news is that it's easy to replace - just buy a new one (they're in the range of 5 bucks), and find someone to weld it in for you. The bad news is that you have to take off the center part of the exhaust to do it, which is a little tedious. If the metal around the bung is badly damaged or corroded, it may have to be patched, and a new hole drilled, but there's plenty of room upstream of the existing bung to drill a hole for a new one. Just make sure you put it on the top part of the exhaust, near the location of the original sensor, because that's where it's easiest to weld a new one, and you need to have the O2 sensor oriented downward to ensure that condensed water doesn't collect in it, which will significantly shorten its life. Here's a picture of my O2 sensor bung:



   

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[MB968]

You might find it easier to drop the whole exhaust. I usually find that the exhaust hanger bolts are easier to deal with.

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[Cloud9...68]

Could be - the bolts connecting the center section to the cat back are a bit of a pain, since they utilize lock nuts which fit very tight on the bolts. But if you have to take it to someone to weld on a new bung, you will still have to separate the center section from the cat back, although this should be easier with the whole thing off the car.



Also, you may not have to buy a new bung - you may be able to get away with re-welding the old one.

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[rl968]

I think my cat might be clogged, which is why the 02 sensor blew off like that, so it will have to go.

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[flash]

i doubt it. you should be able to tell though. if it's clogged, it will glow red and the pulse out the back will be soft and irregular. power will be way off too.



when you drop the exhaust you can see for yourself

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[rl968]

Just got around to this, CAT was heavily clogged.

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[RS Barn]

It's fairly common to see cracks on O2 bung. The sensor becomes welded to the bung and when people try to change them, they crack the weld or rip them out . It can also just crack from heat cycles next to a weld. Similar to the resonator pipes.

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[flash]

we're also starting to see plugged up cats on cars over 100k. common causes of cats going bad are oil burning from things like a bad AOS or bad valve seals, and also from running rich, like from a chip that adds too much fuel. if you watch your readings at your emissions tests, they will indicate the condition, and then you can try to cure it before it becomes a problem.



i'm not sure what we are going to do about it though if it is plugged, since the OEM cat is NLA, and the aftermarket ones don't work very well. i really had to fight to get mine to pass smog on a huge double biscuit cat. no chance on a "hi-flow". in the end, i went back to OEM.

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[94SilverCab]

I just replaced cats (2) on my Volvo S40 at 100K miles, coincidence? I think not...



JMO,,



Jay

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[flash]

feel lucky - that's the designed life expectancy of a cat nowadays. it used to be only 60k miles.



this is going to become the next big problem for us, and why it is so important to keep things running at their best, with no oil burning, and not running rich (especially at cold startup). those are two things that will take out a cat in short order.



it also become increasingly important to keep the O2 sensor in good working order. if it is old, coated, or worse disconnected or bypassed, you will run too rich, and it will really cut down on the life of the cat.

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[Cloud9...68]

Hmmm... So wouldn't bypassing the throttle body heater as many have done (and as I'd been planning to do) also potentially be detrimental to cat lifetime? With no TB heater, the mixture will run richer longer, which is bad for the cat, right?

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[flash]

could be, assuming that you were in a climate cold enough to make a difference. this is why i do not suggest that normally aspirated cars disconnect that hose.

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[Cloud9...68]

Yeah, the impact of disconnecting that hose would definitely be more pronounced in cold climates. What would be needed is a "normally open" thermostat, which would close once the coolant temperature reached a pre-determined point. Probably way more trouble than it's worth, though.

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[flash]

yup - the difference is very minimal. the air is rushing through there pretty fast. the coolant path is really only there to prevent icing and maintain emissions.

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[rl968]

My car is registered as a collectible in NJ so no emissions and I will not replace the cat and instead will have my mechanic install a resonator so that it's not totally obnoxious sounding. The car is manly used as a track car anyway, even though i haven't molested it...much yet. I have my hoses disconnected at tb too and it's chipped. It has be down on power and now I know why. With the 02 sensor the way it was, it was hunting at idle quite a bit. Luckily sensor is still good so will be welded back on. BTW, al of this type of work is being done by Max so I know I'm in good hands.

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[flash]

it might be down on power because of the lack of the cat. that will cost you about 20ft/lbs down low.

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[rl968]

Just heard back, car is repaired and im told feels like it has more power. I'll get it on sat to see for myself.

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[flash]

the exhaust leak you had there would cost a lot of torque, just like opening up the flow of the exhaust. this car needs restriction to maintain low end. porsche even went so far as to choke down the collector in front of the cat. not having the O2 functioning would mess up the mixture too. i can imagine you were down quite a bit on low end. you could gain some more bottom end by putting the cat back in, but for a track car, that may not be the most desirable choice, as it would probably cost you a couple of upper end horsepower, and you don't really use the low end on the track anyway.

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[rl968]

Thanks, that's how I was thinking, don't need low end, but a lot of high end. I also had a nasty very loud buzz coming from the shifter at higher rpms. Seems the exhaust was touching the tranny. Now fixed. I have to say, Max @provost really knows his stuff!

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