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Engine revs up on its own, suffocated when giving gas

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  • Engine revs up on its own, suffocated when giving gas

    Hello, I am pretty new to working on cars in general and especially on z31's, sorry for the long post but I'll give some context on what led to this. I picked up an 86 turbo manual a while ago with its fair share of problems. It seemed to be running just fine and I drove it an hour home without any problems so to speak. First thing initially was my digital dash was out, which I heard is pretty common for the power supply to go out. Second was I had found out a previous owner at one point put the battery on backwards before which cause who knows how many problems. I looked in the back and found that they had hard wired the fuel pump straight to the battery instead of through the plugs coming from the ecu. I bought a re-manufactured ecu as the fuel pump wouldn't kick on after it would crank, and that solved the problem. Everything was plugged up to the stock plugs as it should. Then my next problem arose which led to where I am now. I noticed that I had oil seeping from the valve cover on the driver side as it was smoking quite a bit since it was burning right on the headers. I stupidly didn't think to just tighten the screws and see if that worked at the time, but it's too late now. I went ahead and disconnected anything holding the plenum on and took it off, as well as replacing the old valve covers with cleaner ones with new gaskets and a little bit of sealer just in case. I heard it doesn't really matter if you put sealer, or not though. I went ahead and put a new gasket with sealer as well on the plenum and reconnected all my vacuum and coolant lines where they were. I almost forgot to mention that i replaced the three injector plugs on the drivers side as the other ones were original and brittle and had the bottom retainer broken. I could tell that the other three on the passenger side were replaced at some point as well. I made sure to reconnect any grounds to where they were before, as the car ran perfectly fine before I took it apart. As when I went to finally start it after putting it back together It idled pretty high for a while and could rev normally if I gave it some gas, but it smelled rich of fuel coming from the back exhaust. Once it had warmed up and the rpm's dropped, if you gave it gas it sounded like it was suffocating through the air filter. I also think I hear a misfire? But I am not completely sure. Anyways then it would come to a sputter after a little bit and shut off by itself. I thought maybe this might be a problem with the calibration of the TPS since I had to remove the throttle cable and such so I tried that with a multimeter and made sure it broke continuity as soon as there were any movement with the throttle. I go to start it again and now the engine seems to rev up high and drop over and over in intervals. I didn't let it run that long as it clearly wasn't running properly. I tried revving it while it did this to see if that changed anything, but it kept doing the same things of revving in intervals. Again sorry for the long post, but I didn't want to leave out any info from the past that may relate to the problem I have at hand. Thanks in advance for any help or advice anyone might have on what is going on.

  • #2
    Try formatting your wall of text into easier to read paragraphs and look for a vacuum leak.

    Triple check all hose connections to make sure none of them cracked when you removed the plenum.


    84 AE/Shiro #683/Shiro #820/84 Turbo

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    • #3
      Also, go back to the plenum and make sure it's screwed down tight.
      --------------
      Legal stuff:
      **Nissan Employee**
      Any information shared is simply my own opinion and NOT the opinion of Nissan

      not legal stuff:
      '88 300ZX 2+2-- Under the knife
      '86 3000ZX 2+2-- the knife victim
      '19 Leaf SV-- Because I hate burning money
      '19 NV passenger-- Because my wife likes burning money

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      • #4
        Alrighty, will keep that noted haha. I will go back through all the vacuum lines whenever I get time, but I really want to go ahead and order all new hoses and replace them anyways so I might do that. I will also double check that the plenum is on tight and to spec. Thanks! Will post an update after I go over everything again.

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        • #5
          I am currently waiting on my new hoses to come in, because I wanted to go ahead and replace them since most of the vacuum lines were rotting anyways.

          One thing I forgot to add in my original post was that I disconnected and removed the cruise control module, would that cause any vacuum problems?

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          • #6
            Which part of the cruise did you disconnect? The actuator assembly requires vacuum and a reservoir. If that source line isn't plugged, that'll be a big leak.
            --------------
            Legal stuff:
            **Nissan Employee**
            Any information shared is simply my own opinion and NOT the opinion of Nissan

            not legal stuff:
            '88 300ZX 2+2-- Under the knife
            '86 3000ZX 2+2-- the knife victim
            '19 Leaf SV-- Because I hate burning money
            '19 NV passenger-- Because my wife likes burning money

            Comment


            • #7
              I actually removed the whole assembly, unplugged and just removed the hose as I was working in the engine bay to give myself a little more room. I didn't even think about the vacuum line just sitting there haha, Ill need to reconnect all of it, hopefully that helps my problem!

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              • #8
                Update: So I reconnected the cruise control assembly and tried to do a little smoke test to see if there were any noticeable leaks coming from any of the vacuum lines. I could see any smoke anywhere so there doesn't seem to be any leaks, though I still am going to replace all the vacuum lines since I have the new silicone hoses anyways.

                I go to start the car again and the high idle was still there, though there wasn't any revving up and down anymore. I looked at my throttle cable though and realized the way I had it adjusted the cable was holding the throttle open a little bit making it rev high. This solved my high idle as well as it revving up and down.

                Now my only problem I feel I need to solve is this misfire, which I'm not completely sure I have. The car also seems to be pretty hesitant whenever I give it gas, almost as if it takes a second to respond to when I press the pedal. The only thing I can think of with the misfire is that the plugs on the injector side are really corroded, so hopefully cleaning them will help as they worked perfectly fine before I unplugged them to replace the harness plugs. As for the hesitation on the throttle I am not sure, maybe I need to adjust the tps again?

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                • #9
                  Hesitation is a very common issue, adjust the TPS if possible but most importantly read up on the problem and you might find something I haven't since there have been so many posts about it.

                  https://z31performance.com/forum/z31...ght-hesitation
                  '85 2+0 Turbo

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                  • #10
                    I adjusted the tps again since I had to re adjust the throttle cable the other night and it did help, just like the other forums said its still there, but seems so be normal. I also cleaned the plugs on the injectors and sprayed them out with some compressed air and it seemed help my misfire problem. The only other thing I might need to "fix" so to speak is it seems to break up if I feather the gas, but revs up fine if pump the gas. I will look around to see if I can find any info on it. As well as the fuel like smell coming from the exhaust. Im not sure if thats a normal thing or not, it also doesn't smoke so I'm not sure.
                    Last edited by GTree; 11-04-2019, 07:39 PM.

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                    • #11
                      Well I decided to take the car on a little test drive down my neighborhood and see how it drove, since it would run perfectly fine sitting in the driveway other than the fuel smell coming from the exhaust.

                      At first, everything was going well. Car seem to drive smooth and didn't seem to hiccup at all... until I go downhill with it. Going down hill I notice the car isn't revving really or it is hesitating whenever I try to give it gas. After going down hill it just seems to sputter and slow down no matter how much gas I try to give it until it dies. I guess since the car is warmed up it starts burning oil on the driver side again, from what I think is the still dried up oil on the exhaust that leaked on there when the valve cover was still leaking.

                      So, I restart the car and it seems to hesitate a bit, but I am able to get it back into gear and it drives relatively normal back up the hill until I am able to park it back in my driveway.

                      I am starting to feel defeated with this car, and it is making me have second thoughts about trying to fix it all. I am going to run the codes on the ecu and see what I get, for some reason I haven't done this yet but will update the post on what it says.
                      Last edited by GTree; 11-05-2019, 04:17 PM.

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                      • #12
                        So I tried to follow the procedure on how to check for fault codes, but not sure if it was right or not? Both led's would flash several times and then followed by the green led flashing by itself. Say it would flash both led's 4 times followed by the green led 1 time. This is a refurbished ecu as well that I got from autozone as my other one went bad. Could it just be flashing both led's for 10's and green for 1's?

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