Installing Mufflers | How many oxygen sensors on exhaust assembly?
08-18-2018, 03:32 PM
#1
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Installing Mufflers | How many oxygen sensors on exhaust assembly?
Hi guys,
I've had it and just want a quiet cruiser. The owner before me had cut the mufflers out and made the car a straight-piped nuisance. Sure the car sounds good at times, but it sounds good to spectators outside the car; the drone inside the car is now unbearable. It simply does not fit this car's caliber to be obnoxious and so damn noticeable on the roads.
Anyway, I'm about to buy the two rear mufflers, and the centre muffler. Related items that appear are: oxygen sensors, exhaust brackets, hangers, and mounts. The exhaust hanger and mount combo and the oxygen sensor I feel are a must. However I need to know how many there are in total.
Thanks in advance, guys!
I've had it and just want a quiet cruiser. The owner before me had cut the mufflers out and made the car a straight-piped nuisance. Sure the car sounds good at times, but it sounds good to spectators outside the car; the drone inside the car is now unbearable. It simply does not fit this car's caliber to be obnoxious and so damn noticeable on the roads.
Anyway, I'm about to buy the two rear mufflers, and the centre muffler. Related items that appear are: oxygen sensors, exhaust brackets, hangers, and mounts. The exhaust hanger and mount combo and the oxygen sensor I feel are a must. However I need to know how many there are in total.
Thanks in advance, guys!
08-18-2018, 04:56 PM
#3
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EDIT
So looking at the diagrams on Jim Ellis Audi, I don't see any oxygen sensor(s) on the exhaust assembly itself. I'm not sure whether or not they're omitting any sensors to keep the diagram as simple and relevant to the search as possible or if the oxygen sensors are located else where.
Exhaust Manifold
Exhaust pipe with exhaust muffler
Middle exhaust muffler exhaust silencer, rear
Last edited by Automotive_Buff; 08-18-2018 at 06:06 PM.
08-18-2018, 09:32 PM
#4
AudiWorld Super User
You might not need those sensors, the only ones you might have lost are just after the cats, and that's easy enough to confirm if they are still there.
08-18-2018, 09:34 PM
#5
AudiWorld Wiseguy
Those are the diagrams for a twin turbo V8, presumably a 4.2 V8 TDI given the configuration (ie. not a “hot vee”). The two great big turbos are somewhat of a giveaway. 
08-19-2018, 08:16 AM
#6
AudiWorld Super User
...Find the right parts diagram...but in general it is going to be one O2 sensor on each side just after the final cat--thus two total, together with the two close in by the exhaust manifold. Not clear, but since you didn't mention needing cats, it's possible those final sensors are still there. You should look. Pre cat and post cat sensors are different, so post cat you need the non-heated (simpler) ones.
Yes, I would just get an exhaust system from a junkyard. Then you of course have al the pieces and couplings and such, and hanger brackets are correctly positioned. If it comes off a never touched one, they (or you) will have to cut it since as installed at the factory it is usually one long assembly that goes up and over the back axle area. Audi sells couplings for later fitting of the front and back halves of it.
Yes, I would just get an exhaust system from a junkyard. Then you of course have al the pieces and couplings and such, and hanger brackets are correctly positioned. If it comes off a never touched one, they (or you) will have to cut it since as installed at the factory it is usually one long assembly that goes up and over the back axle area. Audi sells couplings for later fitting of the front and back halves of it.
Last edited by MP4.2+6.0; 08-19-2018 at 08:18 AM.
08-19-2018, 09:33 AM
#7
AudiWorld Wiseguy
There’s two O2 sensors per Cat. One before, one after. So on a 4.2i V8 there’s 4 O2 sensors in total. You need to have them all otherwise it’ll throw an emissions CEL.
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08-19-2018, 04:37 PM
#8
That's Right
Magnaflow makes exhasuts with CATs for this car:
https://www.magnaflow.com/products?partNumber=24364&searchTerm=24364
08-20-2018, 08:33 PM
#9
AudiWorld Super User
FWIW, my answer assumed from the description ("cut the mufflers out") that it was a cat back type set up, or perhaps a hack job was made after the back/exit on the final cats.
As mentioned, major bonehead mod if front sensors were hacked out too, since those are the ones that work closed loop to optimized the mixture and running performance. The front sensors have increasingly moved up into the manifold area, which is now often a forward pre cat. If car has some kind of headers as a mod, then you have to assess that too. The rear sensors are there only to monitor whether the cats are working or not. But they will trigger a CEL if not there and will fail any of a readiness code, MIL/CEL on, or thorough visual inspection smog check.
As mentioned, major bonehead mod if front sensors were hacked out too, since those are the ones that work closed loop to optimized the mixture and running performance. The front sensors have increasingly moved up into the manifold area, which is now often a forward pre cat. If car has some kind of headers as a mod, then you have to assess that too. The rear sensors are there only to monitor whether the cats are working or not. But they will trigger a CEL if not there and will fail any of a readiness code, MIL/CEL on, or thorough visual inspection smog check.
Last edited by MP4.2+6.0; 08-20-2018 at 08:36 PM.
08-22-2018, 08:11 PM
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FWIW, my answer assumed from the description ("cut the mufflers out") that it was a cat back type set up, or perhaps a hack job was made after the back/exit on the final cats.
As mentioned, major bonehead mod if front sensors were hacked out too, since those are the ones that work closed loop to optimized the mixture and running performance. The front sensors have increasingly moved up into the manifold area, which is now often a forward pre cat. If car has some kind of headers as a mod, then you have to assess that too. The rear sensors are there only to monitor whether the cats are working or not. But they will trigger a CEL if not there and will fail any of a readiness code, MIL/CEL on, or thorough visual inspection smog check.
As mentioned, major bonehead mod if front sensors were hacked out too, since those are the ones that work closed loop to optimized the mixture and running performance. The front sensors have increasingly moved up into the manifold area, which is now often a forward pre cat. If car has some kind of headers as a mod, then you have to assess that too. The rear sensors are there only to monitor whether the cats are working or not. But they will trigger a CEL if not there and will fail any of a readiness code, MIL/CEL on, or thorough visual inspection smog check.
It's a rather clean hack job, but a hack job nevertheless. At first glance I don't see any cut, or loose O2 sensor wires. There's no visible wires hanging in the back. At this point I'll just run the two mufflers in the rear without the sensors until I figure out how the original ones are wired.
The front section of the exhaust assembly is perfectly fine. The rear mufflers have been cut out, typical late teen trying to get some cheap thrills from an obnoxious straight-piped V8. Shame how these cars fall so far down in the used car market to owners like that, but that's a discussion for another thread.