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  • 2700rpm hesitation

    I noticed this weekend that my 85NA has a slight hesitation when I accelerate moderately or hard through 2700/2800. It feels fine below and pulls very hard above but there is a definite yet slight hesitation there. She runs strong in every other way.

    The same engine, and damn near everything else, didn't ever do this in my 84. I swapped the 85ECU out and inserted my 84NA Nisutune and stock 84NA ECUs. That made no difference.

    The only difference now is that I have an L&P plenum, ported lower and Jason's phenolic spacer.

    The only thing I can think of is that given the difference in air flow with the above parts I am getting some sort of flow irregularity at that rpm or the ECU maps just arent handling the air at that rpm for some reason. Once I get the turbo injectors here and start tuning I should be able to correct an issue like that but at this point is 100% speculation if that is even the problem.

    O2, MAF, TPS, all the sensors came over from the 84 which didn't have this hesitation.
    Just stand back and throw money.
    Performance costs money.
    Reliable performance costs more.

  • #2
    have you noticed if your motor is hotter then before?

    sometimes when you are running to lean it will cause the engine to run hotter.

    do you still have all your emmisions equipment? and how old is you o2 sensor? have you checked codes?

    i'm just throwing some ideas out there. hesitation can be really hard to track down.
    Attached Files

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    • #3
      Ive got that exact problem, but its around 2900RPMs. I have had it since I got my '85NA and cannot figure out what it is.
      Attached Files

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      • #4
        84z31 wrote: have you noticed if your motor is hotter then before?

        sometimes when you are running to lean it will cause the engine to run hotter.

        do you still have all your emmisions equipment? and how old is you o2 sensor? have you checked codes?

        i'm just throwing some ideas out there. hesitation can be really hard to track down.
        Appreciate the ideas. But...
        Temp- she is running right where she should be. Dash and e-bay gauges agree. (yes I have a gauge in the e-bay as backup, it makes me feel good)

        I have the EGR removed but that shouldn't make a difference since I had it plugged off before. Lee at L&P threads the EGR port for a blocking plug. I still have the idle control and cold start units and they are working as designed. Both working perfectly.

        O2 sensor is pretty new. Guessing it has about 10K-15K miles on it. This is the same sensor I had in the 84. I didn't remove it from my headers when I did the swap. Didn't remove the headers for that matter. :wink:

        No codes.

        What gets me is that this hesitation is at a specific rpm, 2700-2800, its hard to say with a digi dash and as I am accelerating, but it is a very short range regardless.

        Once the dash reads 3K the engine pulls very hard, and it feels good below as well, just like it did in the 84 but add in that brief hesitation.

        I want to add Russ' cam gears this weekend but I want to get an idea as to what could be causing this first.
        Just stand back and throw money.
        Performance costs money.
        Reliable performance costs more.

        Comment


        • #5
          Is it that transition between the injector firing?

          Terrible idea putting those wheels on...

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          • #6
            that was going to be my next guess.

            its early vtec on a nissan. (just kidding)

            mine doesn't seem to do that. i still have the stock plenuim. all my emmisions crap is gone and i'm running an 88 ecu. mine pulls hard from 2000 rpm up.

            how about timing. is it still set the same. since you are able to get more air throught the motor you could try to advance it to see if it helps any.

            i set my timing about 7* advanced since i am at a higher altitude and have a free'r air flow then stock. it seemed to give it more power, butt dyno.

            have you installed your adjustable cam gears yet?

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            • #7
              Are you guys refering to the transition between sequential and batch firing?

              Damn, I didn't even think of that. Hell, the digi rpm tends to lag a bit so it actually could be. 2800/3000, lag could account for that.

              Hmmm...not sure there is anything to do other than tune it out with Nistune, if that is even possible.

              I havent touched the timing since I set it while the engine was in the 84. I agree, I may be able to gain a bit with the plenum and Russ' cam gears. I may play with the timing just a bit, but I plan to install Russ' gears this weekend so Ill see what if any difference they make with this and overall.
              Just stand back and throw money.
              Performance costs money.
              Reliable performance costs more.

              Comment


              • #8
                thought of something else as I posted the last time:

                The wiring harness on this 85 hasn't had the recall done. Up until now I actually thought that would be a good thing or at least I wasnt going to worry about it. hmmm...

                Any other thoughts out there?
                Just stand back and throw money.
                Performance costs money.
                Reliable performance costs more.

                Comment


                • #9
                  wait, since when does a Z31 ECCS use sequential injection?

                  I was under the impression it was always batch fire and the M30 has the sequential at low RPM and batch fire at high RPM

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                  • #10
                    My 85 N/A does the same at about 3 grand, starts off pretty quick then sorta lags a little bit till it hits 3 grand & then just shoots off...



                    1985' 2+2 Z31 Non Turbo...
                    1986' 2+2 Z31 Turbo...

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                    • #11
                      Yeah, pretty sure there is a transition right at 3K.

                      Terrible idea putting those wheels on...

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                      • #12
                        wait, since when does a Z31 ECCS use sequential injection?
                        according to the FSM there are two types of injection for the VG30ET engine. Doesn't say anything about the VG30E or NA version. The types of injection are group and simultanious injection. Group injection the 6 cylinders are divided into two groups: 1, 2, 3 and 4, 5, 6. Each group is injected with fuel seperatly once each engine cycle.
                        In simultanious, the 6 cylinders are given fuel twice each engine cycle, only half the volume each time. This occurs when the RPMs are 3000 or greater, injector pulse width is greater then 6.5ms or when the cylinder head temp is below 140*F.
                        So the Z never had sequential firing.
                        The wiring harness on this 85 hasn't had the recall done. Up until now I actually thought that would be a good thing or at least I wasnt going to worry about it. hmmm...
                        If it hasn't been done leave it alone. Change to the turbo injectors and tune from there.
                        My 2+2 may have the same hesitation, but it takes off and runs so well a 3000RPM's that I never worried about it. Best thing I can tell you is never go under 3000 and you won't have any problem.
                        ...and how much HP do you have at 0 boost

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                        • #13
                          thanks for clarifying that, Russ.

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