Announcement

Collapse
No announcement yet.

M42 cyl 2 misfire, destroying spark plugs, NEED HELP

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    M42 cyl 2 misfire, destroying spark plugs, NEED HELP

    Hi all, I have a 91 318is I've been having a misfire problem. The first time I pulled the plugs the ground prong was broken off the spark plug in cyl 2. I replaced it and car ran fine for a day and then it happened again. this has been going on for a month or so. now when I pull the plugs, cyl 2 is white(running lean/hot I think), while the rest are normal. I recently pulled the injectors and they were all filthy, with #2 being the worst by far. Today I replaced all of the injectors, confident that it would solve the problem.. I also switched out the tps, and brand new plugs. well i just took it for a drive and its still misfiring. When cold it runs fine, but when it warms up it misfires at idle and while accelerating from a stop in first and second. it still pulls hard unless I am lugging it, which in that case it will stumble in any gear. I am completely lost, is my motor done? -Doug

    #2
    Can you post some pictures of the failed plugs? Do they look like they are being mechanically broken, or like the tab is overheating and melting off?

    Also, what kind are they? The M42 is supposed to use NGK BKR6EK plugs. You said that the ground prong was broken off, so if your plugs have a single prong they are not the right ones (the NGK's have two).

    The only other thing I can think of which would lead to an issue isolated to a single cylinder would be a failing ignition coil, but if it was failing to fire you'd probably just be fouling the plug with unburned fuel.

    Is there any crud or damage on the toothed wheel on the crankshaft damper pulley? Maybe something is messing up the ECU's ability to track crank position around where it would fire cylinder 2's ignition coil and causing too much advance?
    Last edited by bmwman91; 06-22-2020, 06:05 PM.

    Transaction Feedback: LINK

    Comment


      #3
      Also, maybe cylinder 2 has so much carbon buildup that it is messing up the compression or hitting the spark plug? Carbon buildup on the piston crown can sometimes be significant.

      Transaction Feedback: LINK

      Comment


        #4
        Thanks for your response. I should re phrase- only two plugs were “broken”, I have misplaced those plugs. Hard to tell if they were broken off or melted. Recently the electrodes are not missing but the plugs are covered in white deposits. The picture attached shows 2 plugs that I pulled recently . I was using the 2 prong Ngks but I switched to the single prong iridium ones just to see if it would do anything. They actually made it run slightly better. The crank pulley teeth are clean and don’t appear to be damaged. however I noticed that the crank sensor was covered in oil so I clean it off the best I could without removing it, no difference. I also tried swapping plug wires and coils to no avail.

        Comment


          #5
          Here is the link to photo sorry I had trouble uploading it here. https://imgur.com/gallery/3ds1Pxo

          I should also mention that when I put a new plug in, the car runs almost perfectly for about 10 minutes.

          Also, how could I go about checking for excess carbon buildup? Thanks
          Last edited by bimmer23; 06-22-2020, 10:12 PM.

          Comment


            #6
            Get one of those inspection cameras and shove it down the spark plug hole.

            Comment


              #7
              Should I try sea foam?

              Comment


                #8
                Originally posted by bimmer23 View Post
                Should I try sea foam?
                No, you should keep working find out what's causing the issue and then solve it instead of going for an iffy fix. Start with removing the plug, rotating the engine until that piston is where you can see it and then inspect for deposits of any kind. It figures that you can only have a coil issue, a fueling issue (damaged wire at that injector perhaps), or a single cylinder overheating issue.

                What's the condition of your coolant, low level, changed any time in the last decade?

                Comment


                  #9
                  Swap the coils around and see if the issue follows the coil.
                  john@m20guru.com
                  Links:
                  Transaction feedback: Here, here and here. Thanks :D

                  Comment


                    #10
                    The piston has a thin layer of carbon on it, however it doesn’t look excessive. I put in a new radiator in over the winter and the coolant is clean. I swapped coils and the problem did not follow. I guess I’ll check the injector wires under that black cover next. The car also has a jc chip in it, could that be effecting it? I still have the stock chip.

                    Comment


                      #11
                      I suppose you could also somehow have a coil driver that's always live or some other sort of uncommon driver failure in the DME. Maybe try observing spark on the #2 lead while the engine at idle is running if you feel you can do so safely.

                      Comment


                        #12
                        I think that when the high current ignition coil drivers go, they usually fail such that the coil primary won't get any current (open circuit). At least that is what I recall from the rare instances when I've heard about it.

                        Regarding injector drivers...Injectors 2 & 4 are run in parallel from the same 3 parallel current sink channels on the driver IC in the Motronic. If it was the driver, both would be having an issue (similarly, 1 & 3 are paired). Now, if the plug or wire to injector #2 was messed up, then that one in particular could be injecting too little fuel. You can do a rough check on this fairly easily. Unplug the 3-pin connector for the injector harness and measure the resistance between pins 1 & 2 and 1 & 3. Both should read somewhere between 7.5 and 8.5 Ohms. If the resistance between 1 & 3 is measurably higher than 1 & 2, it may well be an issue with the wiring or plug for injector #2.

                        Transaction Feedback: LINK

                        Comment

                        Working...
                        X