Rotating Mis Fire

Discussion in '1998 - 2011 Ford Ranger' started by Notamechanic64, May 17, 2020.

  1. Notamechanic64

    Notamechanic64 New Member

    2002 Ranger 3.0 6 cyl.
    I'm not a mechanic, I'm a parts changer extraordinaire. Need help on this one. I have a severe miss cylinder 4 mostly, but 6, 3, 5 pops up from time to time as well.
    Changed:
    All Plugs
    All Plug Wires
    Coil Pack (twice)
    All Injectors
    PCV Valve
    MAF Sensor cleaned
    Checked for Vac leaks
    Replaced vac lines.
    Fuel Filter few times

    Any direction you can point me in would be great...I own a food truck in Pcola FL. Right answer will eat free for the rest of your Life.
     
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  3. Juliofrancis

    Juliofrancis New Member

    I had a long saga trying to fix a hard starting problem. I arrived at my solution (took months) only after I borrowed an OBD-II code reader to access live data. The higher end OBD readers have a setting that allows you to monitor engine functions as the engine is running. All the fuel and ignition components were giving out the right resistance and voltages when tested with the engine shut off. I went to the live data to see if there was a fuel trim malfunction but discovered that the PCM and the engine coolant sensor (which tested OK separately -key on engine off) when working together were creating false data. The engine was acting on the assumption it was 90 F warmer than it really was. Stone cold in the morning before starting the live data showed the PCM treating the engine as being 140F. I replaced the Engine coolant sensor and it started and ran OK after that. The sensor I replaced showed the correct resistance when cold (about 44K ohms). Still dont know why this happened. Your issue might be quite different but do a live data check. In my case it showed the problem which was invisible to static testing.
    You did not mention the crankshaft position sensor. It could be feeding weak or false info to the PCM. If the is such a condition it might sent a misfire code (check engine light).
    Also low fuel line pressure could result in misfires. This does not create an OBD code. Your engine has a schrader valve on the Bank 1 (passenger side) fuel manifold so hooking up a fuel pressure guage is easy. A live data fuel trim will show if the engine is running lean or exhausting unburned fuel.
    You should also do a compression test. Leaky valves can cause misfires but usually only on the affected cylinder.
     
    Last edited: May 20, 2020
  4. RangerAl

    RangerAl Member

    Hummm.. I'll take that challenge. Free foods for life (just kidding). I've mentioned to a few posts and noticed you've replaced the spark plugs. You might want to replace the plugs with MOTORCRAFT plugs. Its seem like these engine doesn't do well with anything but their own. If you do buy the plugs, get it from your local auto part store or Ford Stealership. Ebay and Amazon are full of fake plugs.
     

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