And I thought the build for my PT car was expensive.

[riles]

Just did some shopping around for exhaust system repair for my kids Infiniti Q45. He was developing some minor exhaust leaks until he completely blew off the oxygen sensor on the passenger side. Figured I may be able to do a little 'gerry-riging' just to get the car to pass emissions , which of course it's now due for. Well after crawling under the car, I notice it has 4 catalytic converters and 4 oxygen sensors (2 on each bank). Well, realizing i may be getting a bit in over my head, I decided to take it to a few well known and small muffler shops and got quotes from $1400-2400, just in parts, not including the mufflers back.
After the price shock of an oem exhaust system that would cost almost as much as the car is worth , I'm back to trying to rig it up myself. After an exhaustive (pun int.) search, found an aftermarket dual cat (pass. side only) for $298. Next was the search for the oxygen sensors that would be needed and that's where the fun really began, because I have no clue what a downstream and upstream sensor is, which according to the parts I need 2 of each.
I'll keep looking and hopefully can get this done without having to pay some else to finish. That would be a lot of money taken away from the fb mustang build.

[nathanr15]

Upstream o2 is to adjust a/f ratio while downstream is just to comfirm the cat is working

[riles]

Ahhh, so its front is upstream and the rear is downstream. Makes sense since the upstream is the more expensive of the two.
It was the right rear (pass. side downstream) that blew through and set off the check engine light. I figured I could just wire/splice together the damaged one to the 'upstream' working one and the system may just see that it was working ok, not knowing which sensor it was actually working off. But since they are two different types, looks like that may not have worked.
Now that I ordered the new exhaust, and now know what up/down stream is, I'll just order new sensors. Looks like the aftermarket exhaust has the bungs already in place for them too.

[riles]

My main objective here is, just to get the car to pass the emissions and not be offensively loud when my sons drive it.

The fumes wouldn't do too much damage to them at this point anyway. (after the damage that rap and hip/hop has done already)

[aray327]

EBay. I had to replace o2 sensors on my old Infiniti and I found them for cheap there. Also buy a code reader so you can clear the check engine light. Harbour freight sells the reader.