Zed Head

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Posts posted by Zed Head

  1. If you've run the idle speed screw all the way in and the engine still runs then you have a vacuum leak.  Then engine can't run without air and that's what the idle speed screw controls.

    Check the PCV hose under the intake manifold. That's a possible air source.  I don't recall seeing any pictures of your setup and whether it's stock or not.  Wait...I went back and found your picture.  Even the valve cover port is connected to the intake manifold through the PCV system.  All of those holes have to be plugged.

    If that hole is still open put your thumb over it while the engine is running.  Something will happen.


  2. 29 minutes ago, Yarb said:

     End result it runs but at high idle 1500 rpm plus. Tach is not working stuck at 3000rpm. Plugs are sooty but firing. The engine runs smooth but acts like the throttle is stuck. The static tests on the afm seem correct. Looked for vacuum leaks but nothing I can find. Need some help from the forum. I appreciate any suggestions.

    Have you adjusted the idle speed screw?  It's the screw with the big head and the spring underneath it on the throttle body.  You can turn it by hand.  When everything is right you can cause the engine to die by turning that screw all the way in.

  3. Sorry, I might have assumed that they'd be there, separated.  I don't have my FSM files handy, I've been on the road.

    My views on the things Nissan was doing in the late 70's and early 80's is that they were mostly about emissions.  California smog was driving most of the development efforts in the automotive world.  I traveled through LA in the early 80's and I seen what the problem was.  LA was in a cloud, not a natural one.

  4. Edit - responding to CO's post....

    I can't tell what RPM that would be but I've wondered in the past about how much total advance might be seen under certain conditions.  I had a distributor with "11" weights and a vacuum canister that gave 18, I think.  So, 10 + 22 + 18 = 50 degrees.  If I bumped my initial timing up to 14, I'd be at 54 degrees maximum.  The centrifugal maxes out at about 2400 - 2500 RPM, commonly, so it's up there pretty quick.  The vacuum curves are in the FSM.  With your data you could probably put a map together, like the ones you use for programmable electronic control systems.

  5. Actually, you could describe the vacuum level on the port as matching manifold vacuum once the throttle blade opens.  Zero when it's closed, manifold pressure (vacuum) once the blade moves.  

    That's the simplest view.  I think that Bernoulli, and Venturi's, principles have been discussed before as causing higher vacuum at the crack of the blade but I don't think that anyone has actually measured.it.  So, really, it's just none and some.

  6. 1 hour ago, thetwood said:

    What does the third end go to? I think it says to the distributor in the diagram in the EFI manual, but then has a not that it would be for automatic transmissions only. 

    Yes, it goes to the distributor.  Manuals and automatics both have vacuum advance timing also. The port on the throttle chamber is what they call "ported vacuum".  It only has vacuum when the throttle is open, not at idle.  The distributor's vacuum controlled timing advance and the carbon canister both use ported vacuum.


    Ported vacuum port on the throttle chamber goes to both the carbon canister and the distributor.

  7. 7 minutes ago, thetwood said:

     I have line directly connecting the dashpot to the bottom of the throttle chamber. 

    Sounds like somebody has messed with your vacuum lines and was unable to resist the urge to connect a vacuum line to the "Sorry:" piece.  Not uncommon.  The dashpot does not use vacuum, it's open to atmosphere.  Make your vacuum lines look like the diagram.  Get a three-way connector.

  8. So is there only one circuit board in the microprocessor ECU?  Not a board sandwich like the early ones.  Did they shrink the package down, the processor replacing a whole board's worth of components?

    Would be interesting to see what is connected to the processor.  Might also be interesting to compare it to an ECCS ECU.  See if it's a step on the progression.

    Somewhere out there is a list of what some of the components inside the early ECU's do, their functions.  Resistors, capacitors, etc.  superlen has seen it, I think. @superlen

  9. 1 hour ago, AutocraftCollision said:

    When the engine warms up, the idle rises to 2100rpm.  It stays there until coming to a nearly complete stop(~3mph), where it suddenly drops to 900.

    Is it a 5 speed or automatic?

    Your description doesn't quite fit.  You're blending driving and idling together.  Why would you be "at idle" going over 3 mph?  Maybe add some details to what's happening?  Hanging idle speed is pretty common but has several possible causes.

    Her's a service manual link. 


  10. EFI, ECU, microprocessor, "computer", "control",,,  there are a lot of words being battered about here.  The control algorithms coded in to the microprocessor circuitry would tell how much "computer control" was happening.  Just because there's a microprocessor in the ECU doesn't mean it was "controlling" the whole system.  It could be doing one small part, like handing the O2 sensor data.  Response speed would be important for its role in the system.

    The original question was about the distributor being "computer controlled".  Even if there is a microprocessor in one of the EFI ECU's, it wasn't used to control the ignition system. 

    Just trying to keep things clear.


    Don't want to get in to this guys world - https://www.performancechiptuning.com/nissan/240z/

  11. Purely on the content that you posted.  I've known and met people like that.  His first words were a denial of something that he could not know, that the mechanic admitted doing burnouts.  Then a justification of the thing that he said was not admitted to.  I wouldn't trust that guy to work on anything of mine.  You can't believe his words.

  12. On 11/8/2019 at 6:54 AM, 718Miata said:

    “No, he didn't admit that he did burnouts in your car, but burnouts in sports cars on private property in front of a performance shop aren't terribly uncommon.

    It's an effective strain check on the drivetrain of the car, similar in applied force to a spirited acceleration on the road. Oil pressure goes up, fuel pressure goes up, engine, clutch, trans, driveshaft, diff, and axles are under load, and the rear suspension compresses. All of this without leaving the parking lot, endangering anyone, or breaking any laws.


    Classic BS'ing.  Art...