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2 cylinders not firing, this is getting to me..

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  • #16
    I don't know if this helps but my 96 Pathfinder had a bad dist/CAS and it didn't show any codes. Put a new one in and it runs perfect.
    Shiro #443

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    • #17
      [quote]Careless wrote:
      Originally posted by edsz31
      you can unplug the o-2 sensor to keep it from going in to closed loop. I used a 87t ecu so that I would not have to use the restistors.
      I think it needs 2 of the 3 sensors to go into closed loop.

      I unplugged my O2, and it still gets slow as soon as it hits operating temperature, so I'm not sure if just one sensor that needs to be disconnected.

      have you checked your CHTS?
      Shiro #443

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      • #18
        Quote" My car starts to reduce timing, or dump excess amounts of fuel or something, because as SOON as it gets to the operating temperature, it's a SLUG. it accelerates about half as much as it should, but there are no mechanical or heavy misfire sounds...maybe a light misfire or two."Unquote

        Careless, mine does the same thing. I'm replacing all injectors with a reconditioned set that flow at 315cc all within 1-3% of each other,after 25 years of crap flowing threw them I'm guessing some maintenance is due. I've done the CHTS (but not the small harness which I've heard can cause issuses). I also have another distributor but will not replace until I see the injector results
        1984 300zx 50th Anniversary

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        • #19
          [quote]james wrote:
          Originally posted by 85NA2T
          The car will not go into closed loop with the o2 sensor unplugged/missing.
          this does not sound correct to me.

          Isn't closed loop where its NOT reading the o2 sensor

          Open loop is where it is reading the o2 sensor ?

          this is all irrelevant as my car has no o2 and I can guarantee it is like this from factory, just like it came with no EGR or catalytic converter.
          Nope closed loop is where the ecu DOES pay attention to the o2 sensor voltages.Open loop is when the ecu ignores voltage readings from the o2 sensor.
          "If your car cant do a burnout from a 60mph rolling start, then your engine needs more work."

          "Nitrous doesn't blow up motors; Idiots with nitrous blow up motors."

          Shooting for 500whp

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          • #20
            [quote]Rick88ss wrote: [quote=Careless]
            Originally posted by edsz31
            you can unplug the o-2 sensor to keep it from going in to closed loop. I used a 87t ecu so that I would not have to use the restistors.
            I think it needs 2 of the 3 sensors to go into closed loop.

            I unplugged my O2, and it still gets slow as soon as it hits operating temperature, so I'm not sure if just one sensor that needs to be disconnected.


            have you checked your CHTS?
            replaced it and the harness twice. it's not the CHTS. I used to get a CHTS code until i changed it, and now I get Code 21.

            I'm going to go change my spark plugs now. I think my gap is too large... maybe not a blow-out but a weak spark.

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            • #21
              You guys are mis-interpenetrating things a bit. The Z31 ecu does not have a 'closed loop' operation. It has 3 different systems for Air/fuel, which are actually just 2.
              The O2 sensor has a 'feedback loop' mode, but it is only used at idle, and when cruising at highway speeds. On all other conditions, this mode is off, so the 02 makes no difference at any other time.
              The AFM and CHTS work together. The CHTS has a 12+ from the ECU, and actually grounds to the AFM. The AFM uses the data from the chts to properly control the fuel/timing curve between cold and hot conditions. When the AFM is malfunctioning, the car goes into a 'safe mode' which I cannot remember the Nissan title for. That's when your car wont rev above 2,000 RPM. The AFM and the CAS share common circuits, and can in rare cases cause codes for each other. Even the FSM recommends checking one before replacing the other in a certain test condition.
              As far as an 'open loop' the way most people think of it, this car doesn't have that. The safe mode in the ECU is the closest thing, but actual open loop allows full engine operation.
              There is also another system in the ECU from 87 on that will assume values for the CHTS circuit should it be considered failed, but that too does not lock out any other sensors from the system. Though the AFM is not a part of the CHTS decision at that point, it still does it's job, as would the fuel feedback system. However when the AFM is disconnected/failed, I don't believe the ECU uses any information from any sensor other than the CAS.
              I learned a lot about the EFI system when my EFI harness melted...

              88 N/A GL
              https://sites.google.com/site/distortionfile/
              My Comedy Website. Who knows, you might laugh.

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              • #22
                As for my particualr case I have not been able to track down another CAS,

                but I have put in 2 more injectors and it is most definitly getting good fuel as the plugs come out smelling wet with fuel.

                but then when i do a plug test earthed to the block the plugs give nice bright blue spark...

                so I can't see it being CAS or anything else,

                time for a compression test, keep it mind its a new motor not run in yet

                so I hope nothing is really bad because I really don't want to tear it apart when it hasn't even done any real work yet.

                Wish me luck
                85 Turbo Slick Top
                __________________________________________________ _____

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