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Thread: Help needed with Exhaust Manifold removal for 2007 Mazda3 S with 2.3 liter engine

  1. #1
    Registered Member

    2007 Mazda Mazda3 S

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    Jun 2017
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    Help needed with Exhaust Manifold removal for 2007 Mazda3 S with 2.3 liter engine

    I'm currently trying to remove the exhaust manifold on a 2007 Mazda3 S with the 2.3 liter engine. The issue stems from the upstream O2 sensor seizing up completely and the nut rounding out when I tried to remove it. Yes, I tried PB Blaster but I'm far beyond any hope for removal at this point. The O2 sensor is now completely destroyed and I basically have to drill it out and weld on a new bung or just replace the entire exhaust manifold at this point.

    I've removed all the bolts and nuts attaching the exhaust manifold to the vehicle but can't seem to route it out of the engine bay. I've tried over the course of a few days with someone helping me. I've removed just about everything I can to get the most clearance including the heat shields around the sway bar and brake lines both on the firewall and the steering rack. It just doesn't seem to be enough and will not come out. At this point, things are getting scratched up pretty bad and the thin foil around the exhaust below the firewall is ripped up pretty bad.

    Does anyone have very detailed instructions on how exactly to remove the exhaust manifold for this particular model? Or does it need to be cut to be removed for this vehicle? At this point, I'm considering replacing the exhaust manifold so cutting the old one isn't out of the question. I just wanted to ask for tips before taking that time-consuming route and being forced to replace the exhaust manifold just for the 02 sensor.

    Thanks.

  2. #2
    Registered Member concept's Avatar

    2014 Mazda3 S GT auto, 2008 MX5 6-speed

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    Have you already looked at a factory service manual for R&R steps?
    2014 3S GT, Deep Crystal Blue, Eibach Pro-Kit, Enkei PF01s, Koni Sports
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  3. #3
    Registered Member

    Mazda3 Sport GS-Sky 2012

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    concept's right, as usual: read the manual. On the other hand, there may not be any procedure to remove and replace an exhaust manifold with the engine in the car. After all, the manifold is already on the engine when the engine goes in the car. It usually comes off only during an engine rebuild, which of course is done out of the car. I'm not saying you need to pull the engine (or drop it out the bottom, since it likely goes in from the bottom) to replace the exhaust manifold, but I am suggesting that there might not be a reasonable method to do the job.

    I assume that the path for the manifold is out the bottom. I would look at what can be removed to provide a clear path, including if necessary the crossmember or subframe... complete with suspension. It may seem extreme, but it's worth considering.

  4. #4
    Registered Member

    2007 Mazda Mazda3 S

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    Jun 2017
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    Thanks for the replies. I was overseas so I just got back to the task.

    Yes, the service manual calls for the cross member, sway bar, and the steering rack to be removed for the exhaust manifold to be removed from the vehicle from below. That is way more than I wanted to get into for the job especially since the car is driving from Maryland to California in 2 weeks. However, searches on Mazda3 forums and youtube show that it can be removed from the top but it may depend on the engine size and/or model year. It wasn't coming out no matter what for this 2007 Mazda3 with the 2.3 liter. However, I went back to attacking the original problem which was the seized and stripped out upstream O2 sensor. Even with many applications of PB Blaster and a pipe wrench at it, it seemed like it wasn't coming out. I went to look for an Irwin bolt extractor as a last attempt but no one carried one in store for a 22mm nut. While at Lowe's with no other options, I bought an Irwin Vise-Grip that was on sale as a last try before taking it to a pro who'd have to probably weld a nut on. The size of the vice-grip was just right for rotation clearance and with its vise-grip, it finally came loose! I now no longer have to remove the manifold from the car.

    The O2 sensor threads in the manifold are rather messed up but I had bought a thread chaser for it. With anti-seize, I was able to re-thread the hole. The chaser now screws in decently, but when hand-threading the O2 sensor, it seems to get stuck. It's rather odd as the chaser and O2 sensor are the same 18 x 1.5 mm thread size. I'll have to look into it further as I don't want issues with the new O2 sensor.

    Given the exhaust gaskets were removed in my attempt to remove the manifold from the car, I'll be replacing those with brand new ones.

    I've replaced many O2 sensors over the years in all kinds of cars ranging from Subarus, Chevys, to VWs. I've never had a problem with any of them until this Mazda. Researching about it, it does seem that Mazdas have an issue with these seizing up and causing headaches for owners and mechanics. I'm glad it's finally out. The lesson learned with Mazda O2 sensors is to expect difficulty so to preemptively use PB Blaster and remove the heat shield from the manifold for better access to the O2 sensor's nut.

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