PO2 Exhaust Leak After Downpipe Install
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Thread: PO2 Exhaust Leak After Downpipe Install

  1. #1
    Greenhorn
    Join Date
    May 2019
    Posts
    14

    PO2 Exhaust Leak After Downpipe Install

    Hi everybody!

    History:

    I have an AEM CAI and the person before me deleted the secondary cat and welded (very poorly) a 3" home-made exhaust to it.

    I tuned with Steve at E-Tunez with my FlashPro and was very satisfied with the result.

    I recently ordered and installed my Fullrace Catless downpipe and Yonaka 3" exhaust.

    It sounds much less raspy, and power has increased.

    I do get that hiss when I go anywhere above 1/3 throttle, like most catless downpipes.

    However, when I sent Steve my first datalog after install, he replied with the following:

    "These logs indicate an oxygen leak on the PO2 sensor, or the sensor itself is not fully installed properly. Check the exhaust for leaks at all junctions and at the head. If I adjust based on these values the car will lose a fair bit of power. It looks like the MPG is way down based on what I can see."

    I confirmed that the bolts where the downpipe meets the engine are tight.

    I confirmed that the bolts where the downpipe meets the midpipe are tight.

    Questions:

    I reused the stock gasket. Does it need to be positioned a certain way?

    I did not unclip the O2 sensor when I uninstalled/reinstalled it, since I felt there was enough slack in the wires, is it possible that the wire was damaged?

    I left the "cup" on the primary O2 sensor, since there was no intuitive way to take it off, could that be creating a gap?

    The O2 sensor didn't drop, hit, or otherwise become damaged.

    ANY help is so much appreciated.

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  3. #2
    Greenhorn
    Join Date
    May 2019
    Posts
    14
    I chatted with Steve at E-Tunez.

    There were no codes thrown, but instead there was a 25% drift in Air Fuel Ratio, and fuel trims drifting 20%, which he concluded that there was too much air in the exhaust. It went from nice healthy ~14.x:1 AFR to ~20 - ~25.x:1.

    He is saying that it is likely near the primary O2 sensor, near the cast bellmouth. As mentioned in the OP, I reused the stock gasket, which was a thin sheet of metal. I'll be installing a thicker Fel-Pro gasket this evening, and reporting the results.

    If the gasket was the issue, then the AFR should drop quite a bit (normal variation after this modification is 3-5%).

    If the gasket is not the issue, I'll be inspecting the downpipe for possible leaks, and the O2 sensor wires for possible looseness.
    Last edited by msaluta; 11-07-2019 at 03:22 PM.

  4. #3
    Nooblets
    Join Date
    Jun 2018
    Location
    Ontario Canada
    Posts
    36
    What's the cup on the o2?

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  6. #4
    Big Timer!!!
    Join Date
    Jan 2018
    Location
    Winnipeg MB CAN
    Posts
    128
    He may mean the piece the between the o2 sensor and downpipe, kinda looks like a cup or heat shield.
    I reused all gaskets.
    My hiss (I know exactly the hiss you speak of), went away as my tune progressed, Dan @ e-tunes (killer).
    It is possible the sensor is cooked, or a wire bitched.
    Keep us posted, hope you figure it out.

  7. #5
    Greenhorn
    Join Date
    May 2019
    Posts
    14
    I figured it out.

    The hiss is unfortunate but normal.

    The cup I was referring to was the piece that is fixed onto the PO2 sensor that recesses into the stock heat shield.

    First, I installed the gasket between the downpipe and the engine backwards. Directionality matters in this case. I inspected the gasket and the side that has the protrusions faces the downpipe (I had it reversed).

    I anticipated it possibly being a bad/old gasket, so I went to Advance and bought a Fel-Pro gasket, which was much thicker and more sturdy.

    After installing that, all readings went near to where they were on any of my previous datalogs.

    The stock gasket would likely have worked if it were oriented correctly, but I didn't want to unbolt and redo everything in the event that it would've cause any more headaches.

    So in my haste and combined fatigue, I goofed. Lesson downloaded.

  8. #6
    Big Timer!!!
    Join Date
    Jan 2018
    Location
    Winnipeg MB CAN
    Posts
    128
    holy thats good info, and a thicker gasket is available, which is nice, i may snag one just to have on hand.
    thanks for the update!

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