Random misfire on 4.6

Discussion in '1st Gen - 1997 - 2002' started by mpreece, Jun 6, 2019.

  1. mpreece

    mpreece Member

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    I have a 2000 4.6 with over 200000 miles. I am the 2nd owner of this vehicle, got it in 2002 with 52000 miles. It has been well maintained. I have changed out the plugs and coil packs several times over the years. I am getting random missfire codes at the same time. I have changed the coil packs and plugs on each coded cylinder . Still have a bad missfire! Sometimes it will only be a missfire on #8. I know the plug is good that connects to the coil pack on #8. When it does give a random missfire code it is #3 and #8 mostly coded but sometimes it will be other cylinders? I was driving this vehicle almost everyday and it was running fine then started missing really bad and throwing codes.
     
  2. 01ExpeditionXLT

    01ExpeditionXLT Member

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    Have you tried swapping the injectors for 8 & 3 with known good cylinders and see if that cures the problem?
     
  3. mpreece

    mpreece Member

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    I never thought it might be an injector problem but im open to trying anything.
     
  4. grantpa

    grantpa Full Access Members

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    I was having the very same issue with my '00 EB 4.6L. I can "feel" a slight miss or uneven idle. It's very slight and hard to detect, but I can feel and hear it. I've replaced COPs, plugs, and switched injectors to no avail. Took it to a Ford "specialist" who claimed they had Ford scan capability that I do not. $500 bucks later, all they did was replace (unnecessarily!!!) one plug that they claimed the porcelain was cracked-I had just replaced that very same plug 2 months prior. When I asked for the broken plug, they said it was tossed since I didn't request it before work commenced. Hmmmm. Anyway, they said there weren't any codes, pending or otherwise.
     
  5. Trainmaster

    Trainmaster Old School Member

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    Injectors, coil boots, engine compression, head gasket, valves?
     
  6. studabaker

    studabaker Full Access Members

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    So i took mine to the dealer once and i was shown a print out of the misfire on #3 which was not sending a code. I ended up replacing the pigtail today and it s running good. A low voltage getting to the coil pack could be from pulling on those conectors over the years. Half of the wires broken inside the plastic would be hard to id. I got the pigtails from amazon. I ate pork tonight. This has been a vibration ive been trying to find for years. i am finally done. Theres hope. in hind sight i would have a mechanic do the pigtail for me. I used two part pressure connectors, left over from radio installs. Soldering in the engine bay made me nervous too near my ac lines n stuff. I started to do that, its the best connection but my way is working.
     
    Last edited: Jun 20, 2019 at 4:48 AM
  7. TobyU

    TobyU Full Access Members

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    Do you not have a scan tool with results that will show misfire counts? This would have shown #3 racking up counts and not the others.
     
  8. mpreece

    mpreece Member

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    Yes I have a scan tool. #8 is the primary cylinder that shows up the most, but #3 will pop up sometimes and it will say random misfire. It is not using any oil just a bad miss. I have changed the coil pack and spark plug, still no change.
     
  9. Ron1978

    Ron1978 Full Access Members

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    Make sure to look in the spark plug area for coolant, my dads 2002 4.6l has a intake gasket leaking and it will throw a code about miss fire, after we looked at it better the water was Corroding the end of the wire on the coil pac breaking the connection between Coil Pac and plug, this is very common on these motors after 150k miles I’m told
     
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  10. TobyU

    TobyU Full Access Members

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    That sounds more like a hard code that pops the light or even a pending that is a P0303 or P0308.
    I'm talking about the "test results" as my old Auto X-ray calls it. $6 I think is how is it marked on it. Many of the cheaper ebay ones do the same now.

    I go to test results and scroll down 4 times and I'm in the cylinder misfire counts. It shows cyl 10 and 9 even by default too but then 9 down to 1. Each one has a 0000 or a number or misfires it sensed over the whatever period of time or since the last code reset.
    It is invaluable for finding misfires that are not strong enough or regular enough to set a code.
     

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