The 2001 XJ we are rebuilding has dual catalytic convertors on the exhaust manifold with the dual O sensors.
is there an easy why to modify to a more traditional single cat farther down the exhaust line?
Could I use a non Cat exhaust manifold and just put a single cat down line with a single O sensor? what would the computer do when it only sees 1 O sensor input?


This will be a strictly off road, unregistered XJ to be used on my 1200 acre ranch


Slack

 

Nope. Best way if the cats are not clogged is to leave it alone.

 

I have p0420 and p0432 so I'll be needing to swap my cats anyway... Easy solution for me to revert to the prior 99 style? I always figured you could just get a junkyard ECU to handle the change.

 

Nope cheapest way is to replace the cats...$180 on eBay

99- have distributor, exhaust port size is different..would needed a $120 exhaust adapter gasket https://jeepexhaustadapter.com/purchase/

 

ah. very true. so swap the engine and exhaust and ecu

 

Not really.

Let's just say it's extremely doable, as I may or may not have done it myself.

A theoretical parts list:
- A different PCM
- Different Exhaust Header
- Different Downpipe to Cat
- An O2 connector out of a parts XJ for Rear O2 extension

Is it legal...not exactly.

Does it throw any codes...nope.

 

Totally legal so long as it passes emissions per state. No longer against CF rules either so no need to hide whether you've done it or not lol.

 

That parts list is not complete. If you think all of that is worth cost/labor over putting in the correct exhaust then go ahead.

 

Eh, not exactly. I know it will pass emissions, but removal of factory equipped Catalytic converters is still a no no.

Uh, yeah it is...I've done it.

And yes, it was WELL WELL worth it over the 2001 dual precat system, with 4 O2 Sensors.

I would do it again in a heartbeat.

I no longer have an exhaust tri-bolt flange that sits LOWER than the pinion, asking to get hit and taking the manifold with it. I no longer have to deal with 4 O2 sensors all needing to work in conjunction. I no longer have to worry about the added heat that the precats love to generate.

It is quite literally a bolt on affair. The time difference if you're replacing your exhaust manifold gasket, is maybe an hour, two at most.

 

Unless you get all of that for free how is it any cheaper? He asked if it was easier to swap or keep it stock. Still cheaper and easier to stay stock.

 

Since we are rebuilding the engine, swapping in a 5spd (currently an auto), and replacing the entire exhaust system,,
It's a 2001,, what PCM would work with the rest of the jeep but not require the 4 O2 sensors?


Slack

 

For me, it was a little cheaper than putting new ones on (mine only has 105k on them). If I hadn't bought an aftermarket header, It would have been under $100.

It's not hard to find someone parting out an XJ whos willing to let go of everything from the exhaust header out for cheap.

Ideally for someone looking for a "quick" change out, sure, it's easier.

For someone looking for a setup that's cheaper in the long run, puts off less heat, has and can be made to have far better clearance, then yeah, as mentioned...worth it. I will note though, legalities and inspections are removed from that part of the discussion. If my rig were staying stock, or in an area where inspections/emissions would notice, I'd keep the pre-cats.

2000 XJ with the federal, NOT Cali emissions.

PCM #'s along the lines of 634AE or 634AF.

635 is the CA emissions (4 O2 sensors).

 

Thanks, that's the solid info I needed

 

Could you not just cut the precats out, replace them with pieces of straight pipe, weld two 02 sensor bungs in after the main cat, plug the original downstream sensor bungs and then extend the harnesses of the downstream sensors so they reach the new bungs?

That way you wouldn't have to change the manifold or ECU.

 

One could, I had entertained doing that, but it would have been even more work to do that, without the desired other features.

There's several ways to do things, all depends on your end goal.