exhaust system

[Qxx4]

I saw under the on the passenger side and the driver side the two resonators/cats and I want to know are these the resonators or the cats. I am getting confused and there is one in the middle of the car and at the end what are these.

[skiski329]

The cat's are before downstream O2 sensors. that's how they get measured. anything after that is exhaust pipe and noise reduction stuff (ie. muffler, resonator). So yes, the cat's are by the driver and passenger side of the truck. (for an R50).

[Qxx4]

thx u helped me a lot

[Mark Sheriff]

i also had the same question, but just to be sure, under my pathy i see 4 parts that i need identified, all 4 look like cats, the two upper ones toward the engine i figured were pre-cats and the two lower one, flat and level with the under body of the car are main cats? i am not sure if this is right or not does anyone know?

the upper ones look like this (with o2 sensors before both of these):


and the lower ones look like this (02 sensor is connected to the beginning of the pipe but before the cat(or resonator):


which ones are the cats and which are the resonators?

[CanuckQx4]

The second pipe you pictured is a resonator. There is only 1 cat per side, even looking from the bottom there hard to see, there stuffed way up

[Mark Sheriff]

thank you very much, thats clears up a lot because even when serching for replacement parts, those two lower ones come up as cats, im about to cut those two off because they are all rusted up and one side is rattling near the fex pipe, i have a flowmaster muffler in already and it sounds good but not loud, might be more loud with the resonators off though.

[Buzzman]

Starting from the engine and going towards the rear, the standard (OEM) exhaust system on an R50 (in my case, my 2002 Pathy) has 2 pre-cats (Those fat little buggers you pictured), two "normal" cats, one muffler, and one resonator, in that order.
The resonator is at the very back near the spare tire.

[CanuckQx4]

^^ Alot of people mistake that first resonator as a catalytic convertor, it is just labelled wrong to some distributors. ive had them off 2 cars, there is only 1 cat per side, nissan just likes resonators

[Towncivilian]

There are indeed two "pre cats" and two regular cats. We thought they were resonators too, but that was recently disproved.

[Mark Sheriff]

see this is what confuses me, some people say its resonators, some say its cats, how can we know for sure? my muffler shop says they are resonators also, and would o2 sensors be after a resonator? to me the o2 sensor will be one before the cat and one after the cat, is that correct? my truck goes like this, engine-02 sensor-cat-02 sensor-then comes the resonator or cat(not sure which one) but i know there is no sensor after it. so what is it really lol

now Ive had the resonator by the spare tire cut off and my stock muffler cut off and i know have a flowmaster muffler and chrome tip, the resonator i did cut off, really silenced a lot of the exhaust noise, i had the flowmaster on with the resonator and you could hear no difference from stock,until i cut off that rear resonator that was by the spare tire.

[Towncivilian]

This parts site shows the location of the pre-cats on our vehicles. See item 4 and 5.

[CanuckQx4]

#5 and #12 are 100% resonators, I literally replaced both on my truck less than a week ago. You can buy #5 from aftermarket companies (I bought a walker stainless replacement) for less than $70 a side. Cat's are many times more expensive, hence why the main cat #4 costs $250+ even in the aftermarket

Ive also had a previous R50 worked on at the dealership and had the main cats replaced and was told theres only one per side

It is simply mislabeled on a few sites, probably because it has a heatshield

[Towncivilian]

Eh, you'd think a Nissan parts site would get it right. I'm going to ask Rob on NPORA to get a concrete answer.

[Mark Sheriff]

CanuckQx4's explanation sounds pretty accurate to me, please do get a concrete answer Towncivilian and let us know for sure, thanks

[Towncivilian]

That diagram is very misleading as its a generic diagram and blends two different exhaust systems into one diagram.
There are 4 on the R50 models, two off the manifold and two post cats in the right and left exhaust tubes.
Unless it is a very early 1996 model, then it has only 2 off the manifold.

Part #4 and #5 are the converters.


Part #5 is a horrible picture of the post cat exhaust tubes.

[Mark Sheriff]

if the two "post cats" are indeed cats, they how come there are no 02 senors after those cats? if they were cats, wouldn't the engine need to know what the air flow is like? which means there should be an o2 sensor after it

[CanuckQx4]

The diagram link Town posted, #5 seems to be the only dispute.

Jump under your truck and check it out, look up there.

This is a resonator, not a catalytic convertor


and there is only one canister cat (#4) further upstream.

I just replaced these pieces with my own hands, everything downstream of #4 in the diagram changed with walker stainless steel oem style replacements. Feel free to pay $350 for a resonator if you want to let someone call it a catalytic??

[Mark Sheriff]

im about to take mine out too, i was asking because i wanted to make sure they were not cats, im going to order these:



and put them in, to compliment my flowmaster muffler lol