'99 GXE 1.6 Cat Replacement

[shortlid]

Family memebr has a '99 Sentra GXE, manual 5-speed, and the exhuast is rotted from the bottom of the cat mounted in the manifold back. Got a direct bolt system pretty cheap but Advanced Autoparts wants $450 for the cat for the car!!!!! There has got to be a cheaper option, she dosen't have that kind of money to trow at the car. Anyone could tell me is a header and moving the cat back, or a universal that can be rigged-up?

[nametakennow]

The cat in the manifold is the precat, and replacing it requires that the whole manifold be replaced since it's once piece.

You could get a header and put a second cat on, or sim the signal/move the sensor back/etc. Otherwise you could try finding a used OEM manifold in better condition.

Beyond that you're pretty much stuck.

[shortlid]

Well the system does not have any other cat other than the cat in the manifold on this car. I guessI could get a ebay header for $100 then put a universal under the engine right? Which of the three sections of pipe under the car should I instal the cat?

[nametakennow]

It should have two cats. The first is integrated into the exhaust manifold. The second is underneath the car, roughly abreast of the front seats. If, for some reason (maybe the 1 cat makes the GA16 clean enough, that's news to me), it doesn't have that second cat, ignore "move the 2nd sensor back" under option C below.

Your options are:

A) Get a new/used OEM manifold with the aforementioned integrated precat.

B) Get an aftermarket header (I think OBX has one, Hotshot used to til they went off the map, SSAutochrome may have one too) and put in a universal cat in the piping before the second O2 sensor. This is the idea you brought up.

C) Get an aftermarket header and either move the second O2 sensor behind the main cat (underneath the car), sim the signal, or use a defouler to trick the sensor into reading clean.

Cats aren't cheap, so option C is the cheapest method. An aftermarket manifold in decent condition is going to be $100 at the cheapest, and a decent cat is usually $75+. Going the cheapest route will make the exhaust a little louder, though.

[shortlid]

OK, seems the best fit. So I need to know what small section of pipe to put the universal cat on. The headers I am looking at have a O2 bung in them, will it trip the CEL in the header? What size in and outlet do I need on the universal cat?

[nametakennow]

The sensor in the header is what the ECU uses to regulate a/f, so it's a "raw" (read - uncleaned) reading. It will not trip a code.

You need to put the cat in anywhere after the header and before the second sensor, which is underneath the car. You'll probably have to put it in almost immediately after the header, which could cause some clearance issues with the bottom of the engine.

You'll have to eyeball how much room you have before the second sensor.

IMO, the inlet/outlet should match the piping diameter of the midpipe, which is probably just shy of 2in (I know it is on 00-06's) - that said, '00-06's have a ~2.5in cat on ~2in piping, so take from that what you will. Take off the midpipe and measure it to be sure. Presumably you'll be cutting the midpipe and welding in the cat somewhere along it.

[shortlid]

Great info thanks, anyone got picks of there set-up for me to get ideas??

[nametakennow]

I doubt anyone else has a extra cat installed with an aftermarket header.

[shortlid]

No extra cat just the one, it is New york registered car so does not need Cali. emissions back in '99.

[nametakennow]

Right, by extra I meant universal. Most people probably sim/trick the sensor.

OBDII is across the US, not just Cali. That's why I find it odd that there's no cat underneath the car stock.