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Doesn't like my new AC addition. Surging, sometimes stalls?

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  • Doesn't like my new AC addition. Surging, sometimes stalls?

    Hi guys. I had the PF4 running fine on my very mild 302 for the past year (Although only maybe 500-1000 miles). It's a standard roller 5.0HO with a B303 cam, ported heads, the usuals.

    Just installed a Classic Auto Air system and the PF4 doesn't seem to like it. As soon as the compressor kicks on, the idle starts surging and hunting. I had the idle at 675, now it's at 750. I could probably make it all go away by increasing the idle to 1000 or so, but obviously don't want to do that. Runs fine if I click the compressor off. Also it's fine while driving with the compressor engaged obviously.

    Also had an issue of stalling if I go from moderate acceleration to clutch in/no throttle. I have increased the DECEL Fuel from 1500 up to 1700. Is that about all I can do for that issue? (Proves a little dangerous as it happened while driving in for a lh turn with the light changing. Thankfully it was empty of cars.

    Any suggestions? I could erase all fuel trims and let it relearn with the compressor always on, but then I suppose it may go wonky with the compressor off?

    Any thoughts at all are appreciate. THanks!

  • #2
    Not the safest thing considering what's it doing. But a video/screen capture when it does it would be great.

    And I like the idea of clearing and relearning. Tech line recommends this after changes. And this is a big change in terms of load etc.

    Comment


    • #3
      Try bumping idle to 850, & see how it acts with Ac on.
      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


      • #4
        i had to turn the manual idle screw up then set idle in tablet to 850 runs great and a/c is cold.

        Comment


        • #5
          What's idle timing? Maybe try bumping up to around 20*, if you're not already there. I had to bump mine up when I turned the a/c on, currently 875rpm and 22*.

          Comment


          • #6
            Move to a cooler place.

            Anyways.

            The key is watching the MAP sensor.
            You want to see a noticable change at a idle speed with AC on, and AC off.....this tells the ECU your putting a load on the system......the surging means the idle is not set right....or the AC system might not be fully charged.

            It might be easier to find the needed idle speed if you turn off the Idle Control.......Home screen/Advanced Tunning/On-Off Options/Idle Control.
            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
              Ah, it's only hot here for 2 days of the year anyways!
              Thanks guys, I will try these suggestions.

              I believe my idle timing was at 19, I saw yesterday.

              I do not believe the clutch is kicking in and out, if that's why you are implying not fully charged?

              So one of my concerns is, the IAC is very different with AC on vs off. If I set the idle (let's say 750. I am now unfortunately aware I will have to raise it because of this) and set it perfectly to 12%-18% iac, then turn on the AC. The IAC will drop to 1-2. (Or I may have that backwards. It was late last night I was testing these things).

              So do i want to set the car up/IAC setup with the AC on, or the AC off, because they are two wildly different settings. If I set it up right with zero load, AC off, it will still be wonk with AC on at idle, no? IAC will be completely different?

              Thanks!

              Comment


              • #8
                I know for carburetors they have solenoids that raise the idle when the AC compressor comes on - can one be fitted on the PF4 throttlebody? Then you can have your regular idle RPM and when the compressor kicks on the solenoid will activate and press on the throttle linkage to open the butterflies further.

                Or does this mess with the TPS?

                Comment


                • #9
                  Originally posted by CMerchant View Post
                  I know for carburetors they have solenoids that raise the idle when the AC compressor comes on - can one be fitted on the PF4 throttlebody? Then you can have your regular idle RPM and when the compressor kicks on the solenoid will activate and press on the throttle linkage to open the butterflies further.

                  Or does this mess with the TPS?
                  It messes with the TPS......it will think your accelerating.
                  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


                  • #10
                    Ayup, I was hoping I could sort of have two "programs" in it like my old Quarterhorse could.. but that's ok. I have bumped idle to 850, and reset the fuel curves. Only messed in the driveway and it seems to hunt (wild swings of 75 or so) for a few, but then seems to settle in. Although it always did it worse when hot so I'll see how this goes right now.

                    Comment


                    • #11
                      Originally posted by Stangman View Post
                      Ah, it's only hot here for 2 days of the year anyways!
                      Thanks guys, I will try these suggestions.

                      I believe my idle timing was at 19, I saw yesterday.

                      I do not believe the clutch is kicking in and out, if that's why you are implying not fully charged?

                      So one of my concerns is, the IAC is very different with AC on vs off. If I set the idle (let's say 750. I am now unfortunately aware I will have to raise it because of this) and set it perfectly to 12%-18% iac, then turn on the AC. The IAC will drop to 1-2. (Or I may have that backwards. It was late last night I was testing these things).

                      So do i want to set the car up/IAC setup with the AC on, or the AC off, because they are two wildly different settings. If I set it up right with zero load, AC off, it will still be wonk with AC on at idle, no? IAC will be completely different?

                      Thanks!
                      IAC will go up with a higher load on the motor.......the system will shoot more fuel. Fuel needs air. Hence the IAC will open more.

                      2 types of protection uses on AC..... basically it protects the unit inside the cabin....the part that makes cold air.
                      1. Is a constant run system...POV valve.....think of it as a return fuel regulator.....when the pressure gets to high ( your system will ice over, and plug the lines ) the valve will bypass some freon.........the system will always make the pump run. Constant Run System.
                      2. Uses a simple pressure valve that turns the pump On, and Off....most aftermarket systems are of this type....if the system is low on freon, then the system could be turning on and off inconsistently.

                      I prefer the constant run type ( POV valve link: https://www.originalair.com/restoration-gm-poa-valves ).
                      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


                      • #12
                        I spoke too soon. She's cursed! Swings between 700 and 950-1000. It is aftermarket, Classic Auto Air, but I don't think the pump is cycling.

                        I will see if I can datalog a screenshot-video.. If that's a thing.

                        (It has also occured to me that in addition to the load of the AC compressor, it's also firing up an electric fan. And of course since it's hot out, the second electric fan is firing up. Maybe 35 amp total).

                        Comment


                        • #13
                          I would be watching the voltage of the alternator to find the Minimum Usable RPM.

                          Basically.
                          Turn every thing on. Then shot for around 14 volts in gear......this will be the minimum RPM you can use....same way the Factory does it.

                          You might be needing to replace the pulley on the alternator to a smaller one.
                          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


                          • #14
                            Thanks for the response. I'lll try today, maybe see if I can take a video datalog.

                            Alternator pulley was replaced before I started this AC venture (I thought I had thought of everything. hah)

                            Maybe I'm missing something basic, but how do I datalog so I can graph it? There must be a way to output a file?

                            (I'm also going to try pulling the relays on the fans as it's surging, and see if that clears it up)

                            Thanks!

                            Comment


                            • #15
                              If you have a PCV valve. Disconnect it and plug the ends..... I've seen people have issues some times.
                              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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