Random Misfire i can't figure out

Discussion in 'Mazdaspeed 3 Troubleshooting' started by Rodney Alvelo, Jan 22, 2023.

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  1. Rodney Alvelo

    Rodney Alvelo Greenie N00B Member

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    Hi, so I've been having this issue with my speed 3 for about 2 - 3 weeks now and I still can't figure out what is causing the problem. The car would idle fine but under load it would start to break up. I've done new plugs gapped to .026, I've checked my coil packs and they are good, I've check for vacuum/boost leaks and nothing, I've also done a compression test and is 180 across and leak down was good too but I still have the issue. I just replaced the fuel pressure sensor yesterday and now the idle is a little rough with a pretty noticeable misfire and my HPFP psi will only go up to 1400sh on a WOT pull (before replacing the sensor I would go up to 1900sh) so I don't know if I got a bad sensor or it's normal. I haven't pulled the injectors yet and I'm the 3rd owner of the car so I don't know if they've ever been serviced so I'm going for that next.

    Would like to know if there's something I'm missing because at this point am just guessing and just throwing money at it.

    Please help!!

    I added 2 WOT logs from today hopefully it helps
     

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  2. jsilva

    jsilva Greenie Member

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    What’s the model number of the pressure sensor you used? Was it OEM?

    If you haven’t done it recently, maybe you could run a fuel system cleaner like Techron. I’ve had very good results with it. Worst case your fuel system will be cleaner.
     
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  3. Rodney Alvelo

    Rodney Alvelo Greenie N00B Member

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    Not 100% sure what is the model number. I bought it on autozone. I still have the old OEM one. I tried getting a new OEM one but mazda only sells it together with the fuel rail
     
    Rodney Alvelo, via an iPhone, Jan 23, 2023
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  4. Awafrican

    Awafrican Moderator Silver Member

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    If you bought it from AutoZone and it only reads 1400psi and not 1900 then it's not the correct one. I really wish they would stop selling those things to speed owners.
    Part number should be stamped on it somewhere it also needs to be a Bosch part why did you throw a fuel pressure sensor at it?

    From this thread: https://mazdaspeeds.org/index.php?threads/faulty-fuel-pressure-sensor.15038/

    Bosch 0261545038 is the fuel pressure sensor you need.

    You said you checked for leaks was it visually or boost leak checked? Have you cleaned your MAF sensor? It may be time to clean those injectors
     
    Awafrican, via a mobile device, Jan 23, 2023
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  5. Rodney Alvelo

    Rodney Alvelo Greenie N00B Member

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    I check visually for boost leaks since I don't have access to a boost leak tester at the moment. I haven't cleaned the MAF sensor will do that next. I really am leaning towards injectors since I know the previous owner personally and he mention he never had them service and he bought the car off a used car dealer completely stock.
    That part number you mention for the Fuel Pressure Sensor is the same part number I got from auto zone. Bosch brand too. I still have the box it came on and it's the exact same number
     
    Last edited by a moderator: Jan 24, 2023
  6. Awafrican

    Awafrican Moderator Silver Member

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    Odd did just see another dude say he had issues with a fuel pressure sensor he got from an auto store, but it might not be correct and one dude on the forums got lucky.

    Why did you replace it in the first place? Sounds like your old one was working.

    Might be worth tossing the old one back in and doing the prv test.

    Probably worth cleaning injectors and intake valves given the age of the vehicle as well
     
    Awafrican, via a mobile device, Jan 24, 2023
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  7. Rodney Alvelo

    Rodney Alvelo Greenie N00B Member

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    Replaced it because a friend of mine was having the exact same issue I'm having and it was a fuel pressure sensor so I replaced it to see if that would help but nothing. I still have the OEM one so I'll just put that one back on. I'm just gonna do injector and try my best to clean the valves since I don't have a walnut blaster. Thanks for the help!
     
  8. Awafrican

    Awafrican Moderator Silver Member

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    You can use B12 chem tool and soak the valves then clean them with picks pretty well without the blaster there's a how to here somewhere where someone essentially used a gun cleaning kit. Found it: https://mazdaspeeds.org/index.php?threads/how-to-clean-your-valves.9851/
     
    Awafrican, via a mobile device, Jan 25, 2023
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