mattrourke

yeah, i have the setup without the pre-cats it looks like this (not my exact system, just a picture i grabbed off of google) If i delete these cats and weld in a bung for the downstream o2 sensors there would be no change in the exhaust gasses between the sensors and is my understanding that a code would then be thrown resulting in CEL. Is this correct?

Especial86

iTrader: (1)

As long as you keep the front 2 cats then you will not throw a code
The first 02 measures the condition of the burn before filtering
The second 02 measures the condition of the burn after the first cats filtering
As long as the second 02 is behind the cat it will read a different measure then the front.
The difference in values is what will prevent a cel..
If there was no value change detected by the ECU from the 02's then you will throw a code..
The 02s also inform the computer on how to adjust the mixture of air and fuel. If the computer detects too much air or fuel it will throw a code for a lean or rich condition.

If your first cat has the first 02 in the middle of it, you may throw a code. (you will need a new front cat installed after the first (front 02).... Or plug the bung in that cat and move the 02 in front of it with a new bung.

If your first cat is after the first "front" 02 then you won't throw a code.

mattrourke

With the system I have, as pictured above I only have one cat on each side. The picture shows one sensor on each side right at the join to the manifold and the second sensor is in the cat on each side so by removing the cats I would have straight pipes from manifold to muffler and therefor would throw a code. I'm not sure if the system shown in the picture above would normally be followed by a cat and a muffler but in my case it is just followed by a muffler. Maybe my back cat was already cut out. Either way, it sounds like what your saying though is that I could replace those front ( the only ones I have ) cats with aftermarkets because they would still cause a differentiation in exhaust gases and therefore would not throw a code. Has anyone experienced aftermarket cats causing an irregular fuel mixture?

Especial86

iTrader: (1)

Yeah you get it.

If you got new cats to replace the only 2 cats you presumably have, then you would just need an 02 before and after the new cat of your choice.

Good cats are magnaflow and dyno max in my experience (no codes) and I hear (davico) http://www.davicomfg.com/ has a good reputation ( they also sell full OEM replacement exhaust systems cheap.)

Junk cats are walker, catco, and most eBay no name cats.

Some cheap cats are junk, like I experienced with walker. If I was you I would do 2 " high flow" magnaflow cats with the 02s straddling both the inlet and outlet of the cat. In your case there is seemingly plenty of room to slice the pipe after the first 02 where it's a straight pipe, and just weld in a high flow and add the bung behind it. Code free (as long as it not a junk aftermarket cat)

tlw613sp

Sounds exactly like a heat shield rattling. The shield on my right cat did this only at certain speeds and only up a hill. Sounded exactly like that. Redneck fix: small vicegrips to hold the shield lol.

mattrourke

So, both my cats are toast. Had it all tested and there was no change between the upstream and down stream sensors on either side indicating the cats are no longer "converting" the gasses. I would like to replace with high flow cats and am thinking magnaflows are a nice choice. Since i have the single cat on each side setup with the o2 sensor built in to the cat, what is my best option for aftermarket replacement. I don't really want to pay the extra for the direct fit, would rather swap in a universal of some sort.

any advice?

thanks!