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Discussion Starter · #1 ·
My 2001 AWD needs a new muffler. A muffler shop wants $250 or so to replace it, which seems reasonable. Looks like I can buy a 2-piece kit for $150+ and do it myself when I finish my road trip, but it's not that much of a savings. Anyway, I'm getting a P0101 and 102 codes, which point to an air flow problem, possibly a restriction. The MAF sensor looks clean (I sprayed it) and the air filter is new, so I'm guessing it's the cat or muffler. The air 'tube' after the MAF sensor is intact.The muffler has patches and may leak a bit so it does need replacing anyway, but I'm wondering about the codes. Can a worn out muffler get clogged? I'm hoping the cat is fine, and I don't want to damage it if the muffler is clogged and I don't replace it right away. Thanks.
 

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I suppose it could happen due to a bad muffler and excessive backpressure -- but I doubt it since the MAF is WAY upstream of the muffler and if it was that bad, I'd bet you'd have serious drivability issues. Why do you need a new muffler? is it rattling inside?

Probably unrelated -- MAF sensors are very sensitive devices -- just "looking" clean doesn't mean that it is working properly.

Do you have a scanner can you look at the live data for the MAF? If you're on the road -- you could try a new MAF -- but they aren't cheap. Delco or bust on that part.

FWIW -- I had a p0420 code that was fixed by replacing a broken muffler -- but that is way more likely given the proximity of the downstream O2 sensor.... the MAF sensor is WAY upstream of the exhaust...
 

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Discussion Starter · #3 ·
Apparently a clogged catalytic converter can cause the codes, hence my wondering if a muffler can clog and have the same effect. I don't know enough about how the air flow into and out of the engine relate to one another. Like, if the outflow is restricted in some way, does that slow down the intake, and cause a the 'low' MAF sensor reading? I have a cheap "scout' scanner but have only used it to read codes. I'll check the manual to see if it can do anything more sophisticated. I can also read up on backprobing the MAF sensor to see if it is acting correctly.
 

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I would suspect the Cat... not the muffler.
It's common for them to clog.. but never heard of a muffler clogging
The cat on my ‘92 Chevy Lumina 3.1 broke into a million little marbles and clogged the muffler. If I turned sharply at speed, you could hear the shusshhhh-shusshhhhh of the marbles moving side to side. I had no acceleration at all due to the clogged muffler.

The custom muffler shop had to empty the muffler when they replaced the y-pipe/cat (they had a window in the waiting room to watch the guys work, and watching a million marbles fall onto the guy’s head was pretty effing funny after they told me it couldn’t happen but I had to go back a week later…) - and it wasn’t even close to $100.
 

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I have had to empty one of my mufflers of pieces of cat, it was not a fun/easy job either with the way it's designed, but you could hear the pieces rattling around in there. A clogged cat is much more likely, however you will usually have performance issues along with that.


As far as the codes, there is a huge list of things that can cause them. Have you cleared the codes to see if they come back?
Has anything been worked on recently?


Things I would look at if the codes came back after clearing. bad ground/connectors, vacuum leaks, squirrels storing nuts in your air filter housing ;)
 

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Discussion Starter · #8 · (Edited)
I did the front rotors and pads last week, and inspected the air filter, which I subsequently replaced and made sure it seated correctly. I've yet to test what I can on the MAF sensor, but it appears to be getting 12 and 5 volts on 2 of its 3 pins. I haven't read up on it yet, but it looks like I should get some varying output related to the engine rpm. I've been tricked by codes in the past, specifically an evap code that temped me to chase loose gas caps and the like but it turned out to be the gas tank mounted pressure sensor and the code was because test couldn't even be run properly. I have a hatch above the gas tank so it took me 10 minutes to replace the sensor. I've never inspected the misc. vacuum hoses that exist, apart from changing one that went to the vacuum reservoir. I'm on the road 'visiting', so my research time is limited. The muffler gets replaced on Wednesday, and it needs it regardless of anything else. The codes are erased and I'll see if they come back. They didn't come back after a little driving around town, but I don't know what conditions have to me met for this test to run. No obstructions before the new air filter as far as I can see.
 
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