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Thread: my worst fear, might've finally happened...

  1. #1
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    my worst fear, might've finally happened...

    hey mazda fam. looks like I might be down for a while. I had a sudden misfire happen to me like 3-4 days ago. the car threw a flashing cel and the code I got was P0302. I took it into the shop and they deducted that apiece of a valve is broken off. They said for the work to be done and thats not including misc part or other things they might find wrong along the way to an amount of $2k so at this point i think I might be looking at a new engine or is it something that I can fix on my own with some help? I do love the car and I've invested a lot of time on it and I don't have the money to buy another car atm the only one I would even replace it with would be a much newer subaru impreza. I just find a hatch so much more practical. Any info on where to start to look or maybe if you guys might have a spare engine laying about? thanks
    2002 Mazda Protege5 Pure White

    MP3 Flashed ECU | Mishimoto Radiator/Shroud | MS Door Sills & Shift Knob | OBX Short Shifter with CorkSport Bushings | Goodridge SS Brake Lines | CorkSport 3rd Link Mod | MPV Wiper Stalk & Tribute Nozzles | S2K Antenna | Cabin Air Filter Mod | Rear Bumper Guard with Matte Black Rear Valance | 205/55R16 Kumho Ecsta 4XII on 03 P5 Wheels

    Among the fair amount of maintenance work done.

  2. #2
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    I think you should do a compression test and see if number 2 cylinder is really low.

    Getting a second opinion is a good idea at this point.

    I haven't heard of a broken valve on our car in the 7 years I've been on this site.
    The Diagram Dude

  3. #3
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    Do I just go to another shop or is this something I can do on my own. Im assuming there's a tester?

    Very true and I find that quite interesting.
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  4. #4
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    It's easy..

    You can do it yourself for cheap...
    Just unscrew a sparkplug and screw in the gauge.





    You may just have a bad coil or sparkplug and they're trying to sell you $2000 worth if labor.
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  5. #5
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    Your local car parts store may have it as a loan-a-tool as well.
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  6. #6
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    A misfire is quite often a bad coil with our car.

    Here's the list of possibilities for a cylinder specific misfire.

    (it doesn't mention missing a chunk of valve. lol)

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  7. #7
    The Diagram Dude pcb's Avatar

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    Is your cel still on and is it still flashing or did it just stay lit ??
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    I drove it from San Diego to home and it wasn't till I got home that it began to flash. That was about 80 miles or so.

    According to the shop, they used diff coils and plugs to test the other cylinders and it was just the #2 that kept giving an error.
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  9. #9
    The Diagram Dude pcb's Avatar

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    So it's still flashing ??
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  10. #10
    The Diagram Dude pcb's Avatar

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    Apparently, if an engine misfire is detected the ECU goes into limp mode to stop the misfire.
    It floods the engine with extra fuel and reduces the timing advance among other things to stop it.

    As far as I know, once the misfiring has stopped the cel stops flashing and stays lit all the time.
    Last edited by pcb; 11-23-2018 at 03:33 PM.
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  11. #11
    The Diagram Dude pcb's Avatar

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    If you are missing a piece of your valve you will have very low compression on that cylinder.

    A compression test will show that.

    You may have a bad injector that isn't working right or is completely plugged/fouled. (if your compression is good)
    Last edited by pcb; 11-23-2018 at 03:35 PM.
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  12. #12
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    No, like you have to drive it a little before it does that otherwise the cel is just on but I do have codes p0140 and p0138
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  13. #13
    The Diagram Dude pcb's Avatar

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    P0138 and P0140 are for the rear O2 sensor.
    It looks like your sensor is bad.





    However, it does mention that the code could be caused by low engine compression or an engine malfunction.

    You should still do a compression test to verify the compression.

    As far as I know, the cel only flashes while it's misfiring. If it just stays lit the ECU has stopped the misfiring. (or the other codes are keeping it lit)
    I don't think the ECU can compensate for a broken valve but it may be able to compensate for a while to deal with low compression.
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  14. #14
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    Check compression. Go go oreilly or advance or autozone and "rent" a compression gauge. You pay them up front, and they refund you when you return it. IT will take 10 minutes to do a compression test. IF a piece of the valve really did break off (which i've never heard of before) then you will have no compression in that cylinder. I haven't paid much attention but I think i'm at somewhere around 265-270k miles on my p5. I did a compression test a couple months ago and all 4 cylinders were between 200-210psi as a reference point.

    I'd point more towards spark plugs or a bad coil.

  15. #15
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by pb4ugotobed View Post
    I'd point more towards spark plugs or a bad coil.
    What he said ^^^

    This is what the FSM says about cylinder compression...

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