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engine sputtering and slightly knocking above 5k rpm

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    #1

    engine sputtering and slightly knocking above 5k rpm

    My 2.7 build with a 304 cam is sputtering/knocking above 5k rpm, and I'm thinking its the plugs.

    I have pretty high compression, around 11.2/1, and I've been having problems revving the engine smoothly all the way to redline (6900rpm). I first put in standard plugs (Bosch W8LCR), and the engine wouldn't rev beyond 3.5k no matter what I did. I switched to W8LPRs (plats) because platinum is a 'cooler' alloy than copper, and that kinda fixed the problem.

    Now the engine runs all the way to redline, but it sputters up top. I tried playing around with both fueling and ignition advance (SMT7) with no real luck. I'm thinking I need plugs that are 1 step colder than stock (not half a step like LPRs). What plugs would those be?

    Any other suggestions as to what might be up if it's not the plugs?

    I have a pretty strong spark at idle, and my injectors are 19lbers, in good condition. I have an m30 afm, and that's working just fine, no voltage drop anywhere across the track.

    Help?
    This is your M20 on steroids:
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    #2
    How about gapping my current plugs a little closer?

    Am I at least on the right track?
    This is your M20 on steroids:

    Comment

      #3
      yes, gapping them lower will produce more stable spark, all thought smaller. so i see ou got standalone ecu. thats great. can you verify whether you are running correct a/f rations all the way up o the redline ?

      aswell remote the plugs and inspect them. do they look ok ? try doing a rpoper run, as in wot 1st, wot 2nd, wot 3rd and before you release the throttle, switch the engine off. then stop by on the side of the road and inspect plugs. verify correct temp range of the plugs and a/f rations and timing by reading plugs. if you dont know how to do it, goodle the subject, there are some reat articles on the net about it.

      Comment

        #4
        Originally posted by MrK View Post
        My 2.7 build with a 304 cam is sputtering/knocking above 5k rpm, and I'm thinking its the plugs.

        I have pretty high compression, around 11.2/1, and I've been having problems revving the engine smoothly all the way to redline (6900rpm). I first put in standard plugs (Bosch W8LCR), and the engine wouldn't rev beyond 3.5k no matter what I did. I switched to W8LPRs (plats) because platinum is a 'cooler' alloy than copper, and that kinda fixed the problem.

        Now the engine runs all the way to redline, but it sputters up top. I tried playing around with both fueling and ignition advance (SMT7) with no real luck. I'm thinking I need plugs that are 1 step colder than stock (not half a step like LPRs). What plugs would those be?

        Any other suggestions as to what might be up if it's not the plugs?

        I have a pretty strong spark at idle, and my injectors are 19lbers, in good condition. I have an m30 afm, and that's working just fine, no voltage drop anywhere across the track.

        Help?
        what plugs were you running before you had the problem or have you always had it? Did it just start doing it one day?
        89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

        new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

        Comment

          #5
          Originally posted by digger View Post
          what plugs were you running before you had the problem or have you always had it? Did it just start doing it one day?
          The problem began when I replaced my burned-out 2.7 chip with one that was custom designed for the 304 cam (albeit a 2.5 with a 304 cam). I increased fueling across the range to compensate for the added capacity and air-flow. At the time the chip was replaced, my friend put LCR plugs in there, since they're the stock spec for the e30.

          As I mentioned before, LCRs sucked (too hot), so I then replaced them with LPRs. That for the most part fixed the "3.5k rev limiter" problem, and now the rpms race all the way to redline.

          BUT, when its SLIGHTLY warm out, the car starts sputtering at very high rpms. The problem is much less apparent at night (i.e. when it's cold out).

          I will try regapping the sparks and I will provide feedback.
          This is your M20 on steroids:

          Comment

            #6
            Can someone tell me what plugs would be 1 step colder than W8LCRs and have all the correct specs to suit the m20? I believe there is an NGK plug, which one is it?

            Secondly, could my compression now be so high that I NEED A COLDER PLUG?
            This is your M20 on steroids:

            Comment

              #7
              Come on guys... what's a plug that is one degree colder? SOMEONE'S gotta know...
              This is your M20 on steroids:

              Comment

                #8
                NGK '8' should work ok for you. The colder BP7ES works well for turbocharged M29 engines. '9' is stock temperature. Bosch has the temperature scale the other way around.

                You really need a wideband controller + sensor and preferreably an EGT in near the exhaust port of cyl #6. I don't think different plugs will solve your issues. Better monitoring of the engine is what will diagnose your problem.

                Comment

                  #9
                  Originally posted by iXer View Post
                  NGK '8' should work ok for you. The colder BP7ES works well for turbocharged M29 engines. '9' is stock temperature. Bosch has the temperature scale the other way around.

                  You really need a wideband controller + sensor and preferreably an EGT in near the exhaust port of cyl #6. I don't think different plugs will solve your issues. Better monitoring of the engine is what will diagnose your problem.
                  If NGK '9' is stock temp for m20s, how come the recommended plug for stock m20s is the ZGR5A?

                  Oh, and I regapped the plugs to .6mm instead of the factory recommended .7-.8. Problem solved.

                  Thx everyone.
                  This is your M20 on steroids:

                  Comment

                    #10
                    That seems like a really small gap. Is your ignition system up to par?

                    Comment

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