Fabricating an affordable catalytic exhaust system

Discussion in 'Generation 1 Prius Discussion' started by Bruce Berquist, Aug 19, 2021.

  1. Bruce Berquist

    Bruce Berquist Junior Member

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    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.

    [​IMG]
     
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  2. Bruce Berquist

    Bruce Berquist Junior Member

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    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.
     
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  3. vaughnstark777

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    If it is an American car it has an O2 sensor before and after the cat.
     
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  4. ChapmanF

    ChapmanF Senior Member

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    The HCAC system and valve is about storing unburned hydrocarbons during periods when the cat is cooler. The valve in the cool position forces the exhaust through a HC adsorbing material. When the cat is warmer and the valve shifts position, exhaust gases scavenge the hydrocarbons out of the adsorber and carry them through the cat. (Also, during fuel-cut deceleration when the engine is just pumping fresh air, the valve moves back to the cool position, and the fresh air forcibly scavenges the adsorber.)

    I'm fairly sure the ECM watches the behavior of that valve actuator, and will set one or more of: P1430, P1431, P1436, or P1437, if you haven't somehow mocked it up convincingly enough.
     
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  5. vaughnstark777

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    I’ve often wondered about that. It’s a vacuum motor without any electrical sensors. Plus I’ve never seen any of the ecms with any vacuum lines hooked to them?
     
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  6. ChapmanF

    ChapmanF Senior Member

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    I've seen ECMs with wires hooked to them, and I've seen electrical vacuum valves and pressure transducers, so that'd be my guess.
     
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  7. vaughnstark777

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    I have as well, I just haven’t run into it on the Prius’s that’s all.
     
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  8. Trombone

    Trombone Junior Member

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    2002 here, 145K miles. If my experience is any guide, when the heat valve assembly is not functioning, mileage suffers and the CEL will come on (I forget which codes are set). I bit the bullet and replaced the whole exhaust system with OEM-Toyota parts. How many 19-year-old cars get this far without needing a new exhaust system front-to-back? I like the car so much the cost was well worth it! I'm now back to 40+mpg and the car is loving it!

    If your kludge works and passes inspection with no other drivability problems, more power to you. It's a great little car!


     
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  9. ChapmanF

    ChapmanF Senior Member

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    Knowing that the ECM controls the HCAC valve and has four defined trouble codes for reporting issues with it, how else were you going to guess it did that?


    2001 Toyota Prius Valve assembly, vacuum switching, no. 1. Engine - 2586021030 - Genuine Toyota Part



    2001 Toyota Prius Sensor assembly, vacuum (for e.f.i.). Gen, electrical, efi - 8942120190 - Genuine Toyota Part
     
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  10. vaughnstark777

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    I’d like to give you a definitive answer about whether or not the absence of the HCAC valve can leave a code. From what I can gather, the codes associated with it either show a vacuum leak through rust holes in the vacuum motor or a bad hose etc or a fault in the sensor circuit. I did not make an exhaustive investigation. It looks to me like all you need to do is cap the vacuum line and, as long as everything else is good, it shouldn’t throw a code.

    If you end up with a O2 sensor code my previous suggestion should work.
     
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  11. Bruce Berquist

    Bruce Berquist Junior Member

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    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.
     
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  12. Bruce Berquist

    Bruce Berquist Junior Member

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    Thank you for the info.
    It is very useful, and I am sure that it will be very useful.
     
  13. vaughnstark777

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    50F37E66-A3AE-47A4-AE3A-880F733C9B67.jpeg

    The connector for O2 sensor 2 is located on the passenger side under the carpet up against the center divider area. From underneath you should see a rubber grommet in the same area.

    As far as the exhaust flange bolts. I use this:

    1/2 in. Aluminum Air Impact Wrench
     
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  14. Bruce Berquist

    Bruce Berquist Junior Member

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    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.
     
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  15. dabard051

    dabard051 Tinkerer-in-Charge

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    It may not be obvious, but the downstream sensor wire routes through a rubber boot and a hole under the passenger side rug. To find it, open the passenger door, remove the trim strip and corner foot guard plastic, roll back the rug and feel around with your hand near the center console for what remains of the O2 sensor wiring. If you're lucky, when the theft took place, they either cut or pulled the wires out of the O2 connector harness and NOT from the harness that connects to the Engine Control Module. The O2 sensor connector is VERY TIGHT; you will need a small screwdriver to depress the holding tab and separate the connectors, if the connector shells are still there. My fingers are too big for me to separate the connector shells without that screwdriver to press the tab.
    <edit> this expands a bit on vaughanstark777's artwork and commentary... didn't see his words at the bottom of the picture when I posted.
     
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  16. Bruce Berquist

    Bruce Berquist Junior Member

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    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.
     
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