Fabricating an affordable catalytic exhaust system

My 2003 Prius sedan just had nearly all of it's exhaust system literally ripped out by thieves!

Another problem is that I did not have the type of insurance to cover replacing it.
And another trouble is that I am disability retired and do not have the extra spending resources to afford the crazy prices on OEM and OEM style replacement.

I intend to keep and drive this wonderful hybrid for the rest of my days. It is in otherwise excellent condition for it age at 155000mi.

Having been a 40+ year master auto and motorcycle mechanic I have come to a determination that the only way I can afford to replace this exhaust system is to design and fabricate my own.

I purchased a universal fit OBDII Cat converter ($57) and will install that at the manifold outlet, and then the Cat outlet to a reducer and flex tube down to a 1.5" straight mid-pipe to the muffler pipe.

It will not have the secondary Cat with it's heat valve assembly.
It will not have the resonator (though I may consider installing one if it runs too loud with out it).
The OEM sensors are in excellent condition and are completely in place.

I have done my research and this fabricated system will pass my state, NH, inspection in that it does pass the federal muster of Cat and exhaust system requirements.

My questions that I would like feedback on is:

As I described my fabricated system, is there anything there, or not there, that could cause trouble codes, or cause actual run-ability issues?

There might be a slight variation in the back pressure with out the resonator.
IF there is a slight back pressure variation, will that set of trouble codes?

I know that with out the secondary Cat with its heat valve assembly the main Cat will likely take longer to come up to functional temperature (the primary reason for the secondary Cat and valve), so I will probably have to warm up the system longer before it is optimal. Otherwise, the emissions output should not be an issue.

Any helpful feed back that you can give me will be greatly appreciated.

This well maintained car has run pretty trouble code free for it's entire 155000mi life, except for a recent Hybrid battery related code regarding fluctuating voltage, which was solved when I recreated clean contacts on the battery rail to the individual cells.

Then all was fine, till the exhaust system was gone.

 

Thank you. I will look into that.

According to drawings and specs that I have collected on this year And model, the O2 sensor here is still in place. It is just before the convertors flange connection of the first Cat.
And there are no further wire harness or sensor connection any further down the exhaust.
The diagnostic, when I run the engine with missing cat and mid-pipe acknowledges the O2 sensor but reads trouble code for it. I'm sure due to the open exhaust.

I am encouraged in that those are the only trouble codes that come up, and hope that completing and installing the fabricated section will end the O2 trouble codes.

But you are correct in advising me and perhaps this fabrication might require that I relocate the sensor for best results.

Thank you.

 

Thank you. My thinking is going along pretty close to yours. I appreciate your knowledgeable and honest input on this. It seems that this might become a developmental experiment in fabrication, but so far don't see any unsurmountable issues that may come up.

I can not find any sign that there was a wire for the downstream O2 sensor, but it makes sense that there should have been one. I'm thinking that maybe the thieves tore it out so aggressively that the entire wire got pulled out clean.
I need to find the location of the connector terminal and install a new sensor.
The new Cat came with a bong for an O2 sensor on its downstream side.

All of the parts that I need for this should be on hand this Monday. Then I will be able to complete my fabrication. And then we'll be able to see what comes out of the first test run and diagnostics.

Actually my biggest obstacle at this moment is getting the 2 bolts on the manifold flange loose so I can remove the cut and damaged flange. I have done a soaking of PB Blaster on them and tried to drive them loose with my impact driver with no luck, so I reapplied the PB Blaster liberally again and just letting it set for a few days. Hopefully that will help me get them loose and removed.

 

Thank you for the info.
It is very useful, and I am sure that it will be very useful.

 

PB Blaster and patience worked well and the old flange mount is removed. Phew!
Everything is now assembled and I am just waiting for my O2 sensor order to arrive.

Rather than rushing into the installation just yet, I am going to have a good welder weld and seal up all the seams in the assembly, then I'll remove all the clamps. That will give it good integrity and give it a good clean professional appearance. All the better for at the inspection station also.
I'll post a photo of it before I install it.

 

Okay. The exhaust system is finished and installed on my car. Even with out installing a resonator the muffler does all that is needed to keep things nice and quiet.

No trouble codes are coming up regarding fuel, exhaust, O2 sensors, or anything else emissions related, so I believe that this new fabricated exhaust system has turned out just fine.

On the other hand I did get a Torque Battery trouble code of a unbalanced cells and broken connection. The only Trouble Code that comes up now.

I pulled the cover and terminal rails off of the battery assembly and found a lot of corrosion on the rail terminal connections. Serious enough that I ordered new rails.

Painstakingly, I have tested each and every cell. Trickle charged a small number of low cells to 7.8+v and they are holding charge at a nominal of 7.6v+/-.

However there are 2 cells that easily take the charge to 7.8+ volts but then, with in 30minutes, discharge down to 1.3v and 3.6v.

I am assuming that this is a non-serviceable issue for these 2 cells and that I need to replace them.

I just ordered 2 gen 1 replacement cells.

So it's now off to another phase in my adventure of restoring my "Little Blueberry" 2003 4 door Sedan.

I'll start a new Post for this new phase of my project.