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I have some issues with a 2014 Infiniti QX60 (3.5 V6) that the car repair show is unable to find. I have a misfire code P0300 (random misfire detected). Here are the issues with the car:

  • Car is hesitating when I accelerate
  • When I drive the car for more than 30 minutes, then park for 15 minutes and want to re-start the car, it starts to stumble and then it stalls. I can't even drive it for a bit. And then I'm not able to start it again (stumbling and stalling immediately) and I need to let it cool down for an hour or so. After that it starts like nothing happened. It does not do that every time though.
  • Since the problem started, I have a very poor fuel efficiency (12 MPG)

They already replaced spark plugs and ignition coil. It was better for a few weeks and then it started again. The shop just spent days trying to diagnose the issue and they ended up telling me they think it's the crankshaft position sensors, but they're not 100% sure. The replacement would cost $800 but they're not even sure it will fix my issue. So I would love to have some help from the community before I gamble $800. Did anyone ever experience something like that? Do you have any other idea on what the problem could be? Thanks so much!

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  • Welcome to Motor Vehicle Maintenance & Repair! Dec 22, 2023 at 12:51

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P0017 crankshaft position sensor error. Sometimes the error code isn't generated. Guess how I know? Here's a video; https://www.youtube.com/watch?v=WA-HFPdmFPA. You can diy if you're comfortable working on engines. A well known auto parts site lists crank sensors from as low as $18 to a whopping $57! Dealers and repair shops always markup parts as part of business, paying for overhead costs. Labor rates vary so do your own math to determine if it's worth repair at dealer or repair shop. Personally, I don't know why any repair shop cannot determine a faulty or intermittent crank sensor as it can be measured for resistance values in three temperature scenarios; ambient, freezing (immersed in ice water) and hot (boiling water). If values drastically change, the sensor is faulty.

The entire EFI system relies on a steady timing signal generated from the toothed wheel on crankshafts spinning past the sensor, generating precise timing signals to allow the engine computer to operate; fuel pump, ignition timing for spark and pulse injectors. In my limited knowledge, crank sensors either fail outright (dead engine, cranks but cannot run) or intermittently with engine heat killing the sensor until the engine cools down when the sensor operates again until engine heat affects it. In both cases, a faulty crank sensor renders the ecm unable to operate; the fuel pump, ignition/spark and injectors. The intermittent failure can be a head scratcher to inexperienced repair people without some basic EFI system knowledge and ability to use a multimeter.

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  • Thanks so much, @f-dryer! I'll see if I can do it myself, that could save me a lot of money
    – Calipix974
    Dec 22, 2023 at 2:04

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