NB Miata - Fed manifold in a Cali car

DD#1's 2000 Miata has CEL on with P1141 code.  We went to fix it today and found out that's because it simply has no downstream O2 sensor.

Apparently the PO put a federal manifold in a CARB car.  He moved the upstream O2 sensor to the first bung in the Cali front pipe and there is a neat little professional-looking extended wiring harness for that.  But since that's apparently the downstream position on a Cali car, there is no other spot to install a DS O2 sensor and it is simply removed.

What are my options?  Cheap and easy would be preferred.

1. Get a bung welded into the existing Cali pipe just aft of the cat.  I assume since it is a Cali ECU that I may have to spacer the new DS O2 to avoid giving it fits.  Yes, I know that's probably not legal.  The midpipe is not shiny and rust-free so it may or may not be possible to do this anyway.
    
2. Get a used take-off Federal midpipe with cat and 2 bungs in place.  This is less preferable to 1 because the resonator is a little rusted and the flange at the muffler connection is a lot rusted.  But even if it's everything between the front pipe and the tail, it's probably cheaper than Option 3:
    
3. Get a nice shiny new system including midpipe / cat and muffler section.

I can't do the welding so that will require a trip to the local mod-friendly shop.  I can probably do the other work and make an extended pigtail for the new DSO2.  The exhaust is pretty rusty and I'd like to fix it all while we're under there, but even with me donating the labor and some cash to the job, I doubt DD#1 wants to spend 5 or 6 bills on an all-new system.

Any other options?  Do I have it right?  Thanks.

You forgot to list getting a CA take off and replace it all....  Still an option.

BTW, if 2 is not an option due to rust, I would think 1 would be a real challenge.  If the shop can weld it, that would be the most straight forward solution- and it will probably work, as long as the catalyst that is there is the first one just moved downstream- that's the main one anyway, and should perform well for the test.  

I considered 3 for my car quite a while ago, and missed a great opportunity a few years ago- when FM had an actual header to TP solution that included a catalyst.  Oh well.  They do have a 2 piece solution that should work, and I'm hoping that a NB2 header would work, as they look to be quite effective.  The sum of the cost is less than $900, BTW.  

Lots of people have taken option 1, and it works fine.  No need for spacer, and Racing Beat even used to sell a plug-in oxygen sensor wiring harness extension for that purpose.  I can't speak to the rust.

In reply to alfadriver :

I can get the CA manifold back from the PO but I am trying to avoid going back to the CA manifold because it hurts top end power. 

In reply to codrus :

The rust is really only a problem at the flange end. The pipe itself is pretty clean - but it’s not perfect. 

Duke said:

In reply to alfadriver :

I can get the CA manifold back from the PO but I am trying to avoid going back to the CA manifold because it hurts top end power. 

Stock for stock, there's only a couple horsepower in it.

Duke said:

In reply to alfadriver :

I can get the CA manifold back from the PO but I am trying to avoid going back to the CA manifold because it hurts top end power. 

Still a valid option...   (sometimes being a smart ass does not come across well....)

the KISS solution of welding a bung downstream of the catalyst should work fine.  Just make sure it's mounted in a good orientation to make sure it lasts (tip slightly pointed down, and not really in the way of getting hit by anything).

Is putting a resister in the O2 sensor plug an option?  I ask because that's what I was planning on my 96. 

In reply to Stampie :

No, the O2 sensors generate a voltage, and are not fed on to change via a resistor.  The sensor is generates at 0-1v signal depending on the mixture (mostly .2 to .8V).  You are better off putting a sensor in the exhaust.

They're all really the same option: put a sensor after the cat. They'll all work. There's no good reason to try to spoof the downstream sensor and the cars are often smart enough to detect it.

Keith:

Do you guys sell takeoffs?  I'd love to outfit her with a whole new FM stainless kit, but I don't think her budget stretches that far.

I have a good condition cali manifold and down pipe as well as a good condition fed manifold and  downpipe you can have for super cheap plus shipping.  I also have a 50 state good condition midpipe and the stock axle back muffler section with a resonator welded in place of the big heavy muffler section.  I work best by call or text 334 two zero two 6275

Jim in Alabama 

All cats and bongs are complete and in the factory configurations. 

I got an o2 sensor extension for 15 or 20 bucks shipped on ebay when I went to a header

*BUNGS 

Thanks, Jim!

Other than the O2 sensors themselves, is there any difference between NB1 and NB2 piping?

Local(ish) buddy has a stock NB2 setup he's willing to part with cheap.

Duke said:

Keith:

Do you guys sell takeoffs?  I'd love to outfit her with a whole new FM stainless kit, but I don't think her budget stretches that far.

It's actually illegal to sell a used cat as anything but scrap. Not an issue for a private individual, but we are not a private individual. So sorry, no.

The NB2 part should be good for you.

Keith Tanner said:

Duke said:

Keith:

Do you guys sell takeoffs?  I'd love to outfit her with a whole new FM stainless kit, but I don't think her budget stretches that far.

It's actually illegal to sell a used cat as anything but scrap. Not an issue for a private individual, but we are not a private individual. So sorry, no.

The NB2 part should be good for you.

I thought so on Point One.

Thanks for the confirmation on Point Two.

Dang, going into the scrap pile then!

If you have a stock cat, don't throw it away. They're worth a fair chunk of change at a scrap metal recycler.

The NB2 manifold/downpipe is a reasonably sought-after set of bits as they flow better than even the single cat NB1 stuff. You'll need the matching EGR pipe at the same time.

In reply to Keith Tanner :

I believe I'm getting the stock NB2 system from manifold back.  I'll see if I can pick up the EGR pipe too.

I really didn't want to take the current exhaust manifold off because I'm A) busy and B) lazy.  But the PO had it off not too long ago for the first switch so maybe it won't be brutal.  Exhaust work is not my favorite.  But now is the time to do it, I guess.

Thanks, as always!

Justjim75 said:

Dang, going into the SCRAP pile then!

I did the whole PB Blaster 2 or 3 times a day for a couple days and was pleasantly surprised, no broken studs or stripped nuts.