Converting single cat to dual cat - O2 sensor options

[Al 96 Ram Air T/A]

I'm converting my dual cat car into a single cat using RK Sports/AS&M Mid length headers. The pipes already have emission hook ups with two pre-cat O2 bungs. However, they do not have any post-cat bungs for the two rear sensors. What should I do? What's best for an emission state like NJ?

1) Install two post cat bungs and install O2 sensors (next to each other)
2) Install one bung and delete the other post-cat sensor with SIM or programming
3) Delete both sensors with SIMs
4) Delete both sensors through programing


I'm going to get the computer performance tuned (MadZ28) after the mods are complete. Not only do I not want to throw any codes, but in NJ, they hook-up to the computer. If I use SIMs or delete through programing, can the DMV detect the change? I should pass a sniffer test, as the cat is fully functional.

I already know changing to a single cat can be an issue, but I'm hoping if NJ asks, telling them my previous cats failed after 13 years will be enough of an explanation. If they ask why I now have 1 instead of two...well that may be a tough answer to have them buy off on. I'll have to keep my fingers crossed.

[Rob B (shoebox)]

If they go by Federal law, you will be in violation. Federal law does not allow any change in cats or position of them.

[Al 96 Ram Air T/A]

I'm hoping the "monkey-brains" at the DMV won't know the difference between one or two cats.

So, what's the best option for an emission state like mine?

[Al 96 Ram Air T/A]

No comments??


Injuneer...what do you think? What will the Jersey Nazi's "live with"? Can they see the disabled rear sensors if they scan the computer at the DMV?

Are SIMS a better choice? I can't seem to find anyone out there that still "legally" sells them. That's why the computer option seems to be the best choice.

[RAF7789]

What's the worst case scenario when you would go get it smog checked? Base your choice on that! LOL

[Jeff_in_Atl]

I'm still trying to figure out why you would want to convert it from a dual cat to a single cat.

[Al 96 Ram Air T/A]

It wasn't my first choice, but I was tired of dealing with loose exhaust manifold bolts.

I saw a used set of coated AS&M/RK Sport Mid lengths for sale with a single high flow cat and bought them. I did a little research first, and most agreed the single cat version was far better than the dual cat for fitment. Injuneer uses them...they gotta be good.

Also, getting the stock cat out of the engine bay is going to make life a lot easier due to less heat and slightly more room.


But, I wasn't thinking about O2 sensors when I did this. Now, I'm nervous about the emission Nazi's in my state.

I've kept this car completely street legal for 13 years...don't want to mess that up now.

[Injuneer]

The most foolproof solution would be to have the two bungs welded on downstream of the single converter. You already have the sensors, and the wiring. All you need is a pair of $5 bungs and someone who can weld. That way there is no question the PCM will look "right".

When the emissions systems are "programmed out" of the PCM, its possible to do it without causing a problem. If you do it incorrectly, you won't get a code for the missing sensors, but you will get a "system not ready" flag when they scan it. I don't know how many not ready flags they allow in NJ. Programmed correctly, you will not get a "not ready". I do not know anything about the actual programming though.

I doubt they will look close enough to notice that you only have a single cat. I've never had them open the hood on my cars or look under them (but I have not taken the Formula for inspection for 7 years). They hook up to the PCM, get the all clear, and send you on your merry way with no dyno check.

Good luck with the AS&M's. They are a great set of headers.

[Al 96 Ram Air T/A]

Thanks Fred...


I think I'm going to try the programming method first. I spoke to Ion at MadZ28 tuning, and he's pretty confident in his ability to delete the sensors without tipping anyone off.

If the DMV does notice something out of the ordinary, I can always revert back to SIMS or adding bungs.

Thanks to all for your advice.