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Won't drive over 2000 rpms

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  • Won't drive over 2000 rpms

    1985 300zx Turbo. Two months ago I was driving and could not get it over 2500 rpms. When I finally eased it home it was not going over 2000 rpms. I have cleaned and tested just about every connection and replaced a lot as well. MAF TPS coils etc. I have researched this extensively and there are about 5-6 other posts I have found on the internet that have the same symptoms:
    z31 turbo manual and automatic,
    z32 NA automatic, maxima automatic.
    I have talked to one that was very savvy and he had to sell his vehicle awhile ago and that person still hasn't figured it out either. One had been able to fix this problem by replacing the ECU and another did the same and it did not work. I have done just about every electrical test and replaced anything that had issues.

    I am about to take a pipe bomb to it and then take it shooting :twisted: :nanan?re . haha

    Anybody have ANY other ideas???? PLEASE HELP

  • #2
    Re: Won't drive over 2000 rpms

    Your mass airflow sensor is bad.

    Comment


    • #3
      Re: Won't drive over 2000 rpms

      Like I said. I have already replaced that

      Comment


      • #4
        Re: Won't drive over 2000 rpms

        With a new one or a used one?

        Comment


        • #5
          Re: Won't drive over 2000 rpms

          Did you ohm the MAF harness to the ECU?

          Comment


          • #6
            Re: Won't drive over 2000 rpms

            New one. Yes i have tested that as well.

            Comment


            • #7
              Re: Won't drive over 2000 rpms

              Does it run any different with the MAF unplugged? If it runs the same, then either the replacement MAF is bad or the harness to the MAF is bad and you missed something when doing a continuity check to the ECU.

              The symptom you describe is the limp home mode (
              Restore it, Don't crush it. They don't make them like this anymore.

              Scott
              85 Turbo, original owner, restored
              93 NA Babied


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              • #8
                Re: Won't drive over 2000 rpms

                FlyingT wrote: The replacement MAF is bad or the harness to the MAF is bad and you missed something
                when doing a continuity check to the ECU.
                ^ That

                Check to make sure the plug is clean and free of corrosion, and is otherwise useable.

                This is a common problem that is easily fixed. It's simple either the MAF is bad and/or the harness connector needs to be cleaned/replaced.

                Comment


                • #9
                  Re: Won't drive over 2000 rpms

                  A car I parted out did that with two different MAF sensors that both tested fine per the FSM procedure. Harness checked out as well. I never did fix the car (found serious rust and decided to part it rather than fix it).

                  Two years later, I tore the engine down for scrap. The harness to the distributor was pinched under the intake from a previous repair. I suspect that to be the cause of the running issue. The CAS and harness may be worth a look.
                  5.3 LSx Z31

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                  • #10
                    Re: Won't drive over 2000 rpms

                    Also make sure that the shielding for the MAF signal wire is intact and is properly grounded. If not the MAF won't work.

                    Comment


                    • #11
                      Re: Won't drive over 2000 rpms

                      Try unplugging the throttle position switch and seeing if the car drives any different.

                      Had a Skyline that shorted the idle switch on the TPS and the car drove fine except for the 2400rpm rev limit. Unplugged TPS and it drove mint.

                      Comment


                      • #12
                        Re: Won't drive over 2000 rpms

                        Mitchd03 wrote: Try unplugging the throttle position switch and seeing if the car drives any different.

                        Had a Skyline that shorted the idle switch on the TPS and the car drove fine except for the 2400rpm rev limit. Unplugged TPS and it drove mint.
                        I went through this as well... My TPS connector was corroded, and so were the pins on the TPS itself (I tried cleaning it, but I got tired of it). I got another TPS From a buddy that didn't have corrosion on the pins. I couldn't get a pigtail, so I ended up making little connectors and sliding them onto the pins.

                        I ended up with limp mode a couple months later. It was a little after I drilled into the MAF to get to the variable resistor screw so I could pass emissions (a few years back, don't have to test now :-D ). I figured I messed up the maf, and ended up spending money to get another one. Of course, when I went to install it, I realized one of the wires from the TPS slipped off, and was touching the other one... :banghead

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                        • #13
                          Re: Won't drive over 2000 rpms

                          Thanks for the input guys. It was the TPS, but still having issues and is steadily getting colder and have been riding my motorcycles (not fun) haha. I pm'd a few of you, that were more on track, with this same description. Now that I have narrowed it down more, please educate me all you can. I am not great with wiring and appreciate all the help i can get.

                          HI. So i changed out the TPS and it worked for a day and it will now rev over 2500, but stutters ungodly amounts. Instead of it idling at 800 it goes in between 500 and 700. I unplug the MAF and it idles just fine, but of course hardly any response and moves as fast as a honda haha.

                          I have the the tps set from at 0.00 while at rest and it only goes to 13.5ish with very little throttle or wide open throttle. I'm so confused. Thanks a lot guys.

                          Comment


                          • #14
                            Re: Won't drive over 2000 rpms

                            85_300original wrote: So i changed out the TPS and it worked for a day and it will now rev over 2500, but stutters ungodly amounts. Instead of it idling at 800 it goes in between 500 and 700. I unplug the MAF and it idles just fine, but of course hardly any response and moves as fast as a honda haha.

                            Did you even check the plugs to make sure they weren't corroded for both the TPS and MAF?

                            Don't rule out the MAF (aka AFM) just yet. If you replaced the TPS and the car still won't rev up past 2000-2500 RPMs then I'd still point my finger at the MAF.

                            http://xenonz31.com/sensors.html

                            Seeing as how both of these sensors are notorious for causing similar issues to what you're having due to corroded plugs.


                            I think your issue is a combination of TPS and MAF (probably just MAF) and is probably not the sensors themselves but the wiring for them both is probably corroded and the plugs probably need to be cleaned or replaced........

                            Comment


                            • #15
                              Re: Won't drive over 2000 rpms

                              I have looked at that site. I replaced the maf sensor and all the readings come back fine. It now idles rough, between 500-700....... horrible :banghead and it sounds like it's bogging down (sputtering) and struggles the entire time. I accelerated faster in neutral going down hill then with it under load.

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