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S14 Operating Issues

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  • #16
    The tacho runs off the coil signal.

    The coil also provides the sparks.

    The ECU provides the signal to the coil by switching off the earth to the coil.

    The ECU provides the signal to the coil based on rpm and load.

    The load signal comes from the AFM. - the load signal influences the timing of the signal ONLY. With the AFM signal not relating to the true load, you still get a spark

    The crank speed/position sensors relate engine speed and position (they tell the ECU if the engine is turning or not) No crank speed/position signal = no spark.

    Start at the beginning of the chain; crank sensors. Check resistance and gap from the ring gear and flywheel peg. Check the continuity of the wiring from the sensors to the ECU. Replace with known good sensors if you can't check with an oscilloscope.

    Check coil power.

    Check ECU earths.
    Sport Evo No.47

    My Sport Evo Restoration


    • #17
      Originally posted by Ironhead View Post

      I hesitate to trash a company, but years ago I sent a set of injectors to RC for cleaning and balancing. When I got them back, car ran horribly. After some frustrating troubleshooting (because I assumed injectors were all good) I finally learned one of the allegedly freshly overhauled injectors wasn't even firing....just continually dribbling fuel.
      I have been using RC for countless sets of injectors over the last two decades. Always perfect. Never an issue. Super nice people and a great company to work with. Highly recommended.
      88 M3 Henna
      95 M3 Orange
      97 M3 Techno


      • #18
        Originally posted by HANDBLT View Post
        But it sat for years with old fuel in the lines/injectors? Need to have them refurbished or pick up a set that are.
        RC rebuilt in June.

        Originally posted by Mick View Post
        What's the condition of the battery? A failed battery can cause issues and *might also be related to the tach not functioning correctly.
        Overkill sized Interstate, four months old.

        Originally posted by Yahweh View Post
        Solid spark on all 4? Each injector getting pulse width?
        Difficult to determine as how the engine runs is/was erratic.

        I failed to mention in the OP that the car is running the Miller MAF conversion. 90% of the issue appears to be the connector at the MAF wasn't making consistent *good* contact. Does anyone have any recent info on this Miller set up? Updates, etc?

        Back to where we are... the MAF connection has been secured and as said, it appears that the extreme poor running aspect is gone. At this point, the engine does cranks but takes two to three sets of 10 second cranking to get it to get running. Makes me think fuel delivery AGAIN.

        It's been driven only a few miles and responds to mid rpm hard throttle but with a bit of hesitation. Not a smooth increase of power delivery.

        We got pulled into the tach problem, my bud connected his o-scope and found good signals coming to the instrument panel. a lithium battery/holder is being considered.

        Will resume soon as time allows. Thanks all for your input.
        "The earth provides enough for everyone's need. Not everyone's greed." Gandhi


        • #19
          Based om your description in the 1st post I'd say your MAF wasn't contacting properly as an S14 will idle without its AFM as long as the idle switch is closed. That's how you babies it home I think?
          Tach issue is separate.
          Remove fuel injectors from throttle bodies and watch the spray pattern and quantity by starting the car whilst the injectors spray into soda bottles.
          Concentrate and start with making it idle.


          • #20
            I second the recommendations on refurbing/replacing the whole fuel system (lines, hoses, filter, etc). I chased issues in my car for a long time before discovering the hard lines were rusting from the inside out. These lines are after the filter so the rust flakes were migrating upstream to the injectors and clogging the screens. My theory is the E10 was attracting moisture (car rarely driven) and the water was settling at the lowest point in the hard lines. I live in HI too so I'm sure the humidity sped things along. I've since stopped using E10 (need to search for stations that supply non-E10).

            If you don't want to just throw money at the fuel system, you can easily check the hard lines by pulling the rubber hoses on either end and shining a light in there. If there is rust, you'll want to pull the injectors and check the screens and consider cleaning everything else out (hoses, fuel rail, etc).