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  • Engine misfire while hot

    Hey Everybody,

    Please help!

    I have a 2000 Toyota prado 3.4L v6.

    It has a misfire only when it gets turned on while warm.


    I have recently replaced the following (all with genuine or high quality products only):

    new battery
    Spark plugs
    Leads
    Air filter
    Fuel Filter
    New oil and oil filter
    New Throttle Position sensor
    New Mass Air Flow sensor

    All the other services are up to date.

    An auto electrician friend ran a code reader on it and it came up with Throttle position sensor error.

    I replaced the TPS and it improved the throttle performance 10fold however the misfire remains.

    I just replaced the Mass Airflow Sensor as I've had issues with it in the past and the problem remains.

    I was told by a mechanic that coil packs often fail under heat so I replaced all 3. It seemed to improve the horsepower of the vehicle but the misfire remains.

    When cool the car runs absolutely bloody perfectly. Which is the head scratching part about it.


    I'm only learning, but it possible I put the plugs in wrong?

    Should I take the cheapest option (I apparently haven't tried) and run injector cleaner through it? ( 4 years ago I had the injectors and cylinders pulled apart and cleaned)

    Please any suggestions are welcome!

    Thanks a lot

  • #2
    Jess, Did you end up getting this sorted out? I have a similar issue wiht my 3.4 v6 .

    Brett

    Comment


    • #3
      this does sound like a injector issue as jess covered most there is to cover. coil packs are another issue that can cause his problem . i would start with a strong injector cleaner, then clean the mass air flow sensor with the right product then plugs ect, good luck chasing the problem , let us know when you got it sorted.

      Comment


      • #4
        Thanks Tonz,

        I have replaced the MAF and the throttle position sensor. (that fixed a long standing issue with kick down). I have swapped the 3 spark plug leads . Plan now is to measure the injector coil resistance to see if there are any out of spec.

        It started not long after a big 200k service (not immediately after but maybe a week after). I changed all the fluids, engine oil, transmission, diffs's . Spark Plugs (like for like and have even swapped back to the old ones now thinking they may have been faulty)

        My symptoms are on initial startup when cold when it idles fast it is pretty good. When it warms up a bit the missing gets quite noticeable. And if you are sitting at the lights and accelerate it hesitates and misses until you hit pretty much 2000 RPM then all is good again. Same if you are cruising and it is between 1000 on 2000 rpm it is missing quite badly.

        Onward and upward.

        Brett



        Comment


        • #5
          Pretty much describes the problem I had about 9 months ago. Tried plugs as they hadn't been changed for about 150k but no difference. New leads and coil packs and all good since.
          1997 petrol auto, 430 000km. Still going strong.
          2004 petrol auto, 233 000km. Cracked dash and no help from Toyota!

          Comment


          • #6
            Thats a thought a faulty new plug , just the sorta thing to drive you crazy.,,,,yes i think your being wise to check those coil packs ... how is it though , you go out of your way to service it ,plugs cables filters change all the oils that have oils and even what ever doesn't have oils just to keep it well and healthy , and thats when you start having problems . i sympathize for you .

            Comment


            • #7
              Hi Again,

              Update, so have not worked on this for a few days. But today I had some time to have another crack at it. I removed the cam timing belt cover which was easy to do to double check the Cams had not jumped position since i changes the belt some 50k ago. Confirmed via the marks that cams and crank line up perfectly at TDC. So that is not the issue. Cover back on.

              I also did the School run and noticed the main tank was getting low so I switched to the Aux tank and within about 15klms things were improving. Did the return school run now and things are getting even better. It is running so good that if you wern't looking for a miss fire you would never even know it was there.

              Can it be that the main tanks just had dirty fuel? We will see how this progress's . I will not full up the main tank now until I get a chance to drain it completely just in case.

              Regards

              Brett

              Comment


              • #8
                Sooooooooo, it turned out to be 1 fuel injector was wrecked. So we had that replaced and all the others sonic dipped and all good!!! Tonz - Sorry I only just saw this and you were 100% correct. Car was at mechanic for 12 WEEKS while they diagnosed =|

                Comment


                • #9
                  12 weeks thats insane!. ....but finally its sorted happy days .. well untill you get the bill .. but happy days afterwards hey.

                  Comment


                  • #10
                    Originally posted by Jess Canary View Post
                    I was told by a mechanic that coil packs often fail under heat so I replaced all 3.
                    I was told this is the reason my 90 series is misfiring, but how do I go about replacing the coil packs, leads and plugs? Find a service manual somehow?

                    Comment

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