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Engine Won't Reach Air Fuel Ratio Setpoint

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  • Engine Won't Reach Air Fuel Ratio Setpoint


    Hello guys!

    I installed Pro Flo 4 kit on my 302 Mustang last year. I could not get it to work properly before I stored it for the winter. Spring came along and now here I am.

    So this morning, I went to check it and to start it. I got it to start on first try but it was the same problem as I had before I stored it, it is running badly. It won't stay running at idle. I managed to heat it to 165F and then, when I released the throttle, it finally kept on running (even though I could hear the sound and it was definitely not normal). I got a couple of screenshots.

    On the first screenshot (#1), the AFR is 10 and won't reach SP of 13,4. Second screenshot (#2) I gave a little bit of throttle, engine went a little above 3000RPM, AFR is much closer to SP. Third screenshot (#3), AFR is still too low but a little better than the initial 10. Checked my sensors in the meantime (#4) to make sure everything was okay. Second to last screenshot (#5), finally reached 165F, so I released the throttle. Engine stuttered a bit but stayed alive. It reached the idle target of 950RPM, but it still pretty far from the 13.4 AFR SP. I also noticed 70% IAC, is that normal? Finally, last screenshot (#6), same as the other one, idling but AFR is too low and won't reach setpoint.

    1.png 2.png 3.png 4.png 5.png 6.png

    Do you have any ideas what could stop the AFR to go up and to reach its setpoint? Any suggestion welcome. Thank you!
    Attached Files

  • #2
    What engine?
    Vehicle make & model?
    What Base MAP # is it on?
    Fuel pressure ?
    Hot engine idle vacuum?
    Injector size ?
    HP level ?
    Spark control settings ?
    Don't get too caught up in the numbers.
    Just give the Engine what it wants &
    Let the numbers be what they are.

    Jim McFarland....

    Comment


    • #3
      Thanks for the quick answer, that sure was fast!

      - Engine is a Ford 302, stock cam
      - Vehicle is a 1972 Ford Mustang
      - MAP is 5000
      - Fuel pressure when idling was about 40.2psi
      - Vaccum was about -13InHg when idling
      - Injector size is 29
      - HP level is 400
      - As for spark control, I haven't changed anything, so everything is default

      Comment


      • #4
        13 - 14 " hg. vac when at operating temp, you should be on a MILD cam MAP.

        Try 5002 & see how the fuel trims are correcting.

        Don't get too caught up in the numbers.
        Just give the Engine what it wants &
        Let the numbers be what they are.

        Jim McFarland....

        Comment


        • #5
          Also look at your Short fuel trims. Theyre close to -30. So the ECU is nearing its max of how much fuel it can pull out. Even still your AFR is in the 11's. This is why it cant reach the set point. The ECU just CANT pull enough fuel out. (Side note when the AFR reading is 10 that means the 02 sensor is not yet online).

          try and load the map 2700cast recommended but you might also need to use the Global Fuel Modifiers to get it within proper range.

          Comment


          • #6
            A stock 302 camshaft ( Melling #SYB25 ) should be making 16 to 19 inches of vacuum at idle.
            Use a actual vacuum gauge. Not the MAP sensor reading on the App.

            1. Rotate the harmonic balancer back and forth. The distributor rotor should move instantly....if there is play, then replace the timing chain and gears.

            2. Spray a little carb cleaner around the intake manifold gasket to check for leaks...if you find leaks, replace the gaskets, and use Gasgacinch on the head surface, and the gasket side that faces the head.
            In my neighborhood, if you open your hood to check your oil, and the vehicle still runs after you close it.......Then your labeled the Neighborhood Mechanic.
            https://forums.edelbrock.com/filedat...?photoid=42773

            Comment


            • #7
              Hello again!

              So today I went and worked on my Mustang and the first thing I did was to load the new 5002 MAP. Guess what... it worked like a charm! The difference was day and night, idles much more smoother now. I even managed to ride it for the first time this year.

              In the next few days/weeks, I will do a little bit of tweaking and tuning and then I should be good to go. One last thing still bothers me though... While I was cruising on the road, I could see the "O² learn" light going on and off, and the AFR was set at 10. I'm assuming it has something to do with the O² sensor? I'm planning to make sure it is still working with a lighter and take a look at the wiring and the harness, but do you have any tips or advice I could follow to help me troubleshoot?

              Much thanks guys!

              Comment


              • #8
                It doesn't LEARN all the time.
                In my neighborhood, if you open your hood to check your oil, and the vehicle still runs after you close it.......Then your labeled the Neighborhood Mechanic.
                https://forums.edelbrock.com/filedat...?photoid=42773

                Comment


                • #9
                  I get you. But shouldn't my AFR still be shown correctly? And I should have precised, but the O² learn light was more flickering than staying green for a while before switching, hence why I'm thinking I have a problem regarding my O² sensor. Does it make sense? Or maybe I'm just paranoid and everything is working as intended?

                  Comment


                  • #10
                    AFR will show 10 while system is warming up, then start displaying correct AFR #s.

                    Drive vehicle for 30-40 miles to get it to self learn.
                    Don't get too caught up in the numbers.
                    Just give the Engine what it wants &
                    Let the numbers be what they are.

                    Jim McFarland....

                    Comment


                    • #11
                      Home screen.
                      Touch "Gauge Displays"
                      Touch "E-Tuner Display"
                      Touch the ?
                      Read the information displayed.
                      In my neighborhood, if you open your hood to check your oil, and the vehicle still runs after you close it.......Then your labeled the Neighborhood Mechanic.
                      https://forums.edelbrock.com/filedat...?photoid=42773

                      Comment

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