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AMC 360 hesitation/lean when cold, and whistle from intake

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  • AMC 360 hesitation/lean when cold, and whistle from intake

    Hi everyone. I have a '79 Jeep CJ5 with an AMC 360 and a Pro-Flo 4 set up that I've been having some issues with recently. I live in Ohio and use this Jeep as my daily driver, so some issues are beginning to arise as it gets colder out. My main issue is that when the engine is cold, it hesitates and goes lean when I get back on the gas after a shift. Just cruising, the AFR is fine. I've seen the AFR get as high as 19.0 when shifting, which is pretty concerning to me. Once the coolant temp gets up to around 160-170, The hesitation goes away and the AFR is back to normal on acceleration. I was encouraged to increase the "cold start enrichment" and have since maxed it out at 10 and still have the hesitation and lean condition when cold. I've also added a pump shot and it did not change much. Additionally, when it is cold started, it backfires and sputters if I hit the gas right away before it warms up a little bit. As far as I am aware, I don't have any exhaust leaks and all of the vacuum lines are sealed up.
    My second issue just started recently. Once the engine gets up to temp, (around 180ish) it will randomly start to whistle from around the intake somewhere, I can't quite pin-point exactly where. The tone of the whistle does not change with throttle. I checked that all of the vacuum lines are connected and they are all brand new hoses. Once I shut the engine off, the whistle continues for a few seconds and then gets to a really high pitch and stops. Has anyone else had this problem? I appreciate any input or advice! Thanks in advance!
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  • #2
    Vacuum leaks can be vexing - pun intended. My favorite way is to use a (unlit) propane torch, run it completely around the throttle body, intake manifold, and anything that draws a vacuum, engine running of course. If engine speeds up, you've found the leak. If you're anywhere near Chattanooga, TN, I'll give you a hand.

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    • #3
      Originally posted by CorkyE View Post
      Vacuum leaks can be vexing - pun intended. My favorite way is to use a (unlit) propane torch, run it completely around the throttle body, intake manifold, and anything that draws a vacuum, engine running of course. If engine speeds up, you've found the leak. If you're anywhere near Chattanooga, TN, I'll give you a hand.
      Never thought about using a torch. I was planning on using Brake-Kleen but all of ours in the non-flammable crap! The good old-fashioned flammable Brake-Kleen is getting hard to find!

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      • #4
        A lot of guys use brake and carb clean, it's okay but I've had better luck with propane, engine rpm's come up immediately when you hit a leak. From personal experience, do not use starting fluid/ether to find leaks.

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        • #5
          For cold start. Go back to the page of the App where you added fuel, and touch the "Advanced" tab......now you can add fuel at the "specific temperature" you are having issues.

          Spray some throttle body cleaner ( not carb cleaner ) down the IAC hole......you probably have a flake of carbon making the whistle.

          What is the part number of the camshaft being used?
          What is your idle vacuum ( use a actual gauge. NOT THE APP DISPLAY ) ?
          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

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          • #6
            Originally posted by BITE_ME View Post
            For cold start. Go back to the page of the App where you added fuel, and touch the "Advanced" tab......now you can add fuel at the "specific temperature" you are having issues.

            Spray some throttle body cleaner ( not carb cleaner ) down the IAC hole......you probably have a flake of carbon making the whistle.

            What is the part number of the camshaft being used?
            What is your idle vacuum ( use a actual gauge. NOT THE APP DISPLAY ) ?
            I'll pick up some throttle body cleaner and give that a shot as well as check for vacuum leaks with some propane.
            I'd have to to check the vacuum but the cam I'm running is a Comp Cams XE262H. https://www.compcams.com/xtreme-ener...c-290-401.html

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            • #7
              Here's a shot of the cold start info.
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              • #8
                With that camshaft and stock heads. You should be seeing around 16" on a vacuum gauge.
                If you have worked, or aftermarket heads it will be lower 1, or 2".
                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

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                • #9
                  So hooked up a vacuum gauge and I'm getting around 12". I found the leak, and it's in the center of the front of the intake. Would this be caused by a leaking intake runner? I have been fouling some plugs with oil but figured the rings aren't seated yet. I included a pic of the leak.
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                  • #10
                    I think you'll see evidence of other leak(s) when you pull the intake. I'm not real familiar with AMC engines but other than PCV, there shouldn't be vacuum at that point. What kind of RTV did you use?

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                    • #11
                      Originally posted by CorkyE View Post
                      I think you'll see evidence of other leak(s) when you pull the intake. I'm not real familiar with AMC engines but other than PCV, there shouldn't be vacuum at that point. What kind of RTV did you use?
                      Exactly what I was thinking. I didn't assemble the engine but the builder said he used AC Delco Grey RTV

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                      • #12
                        When you remove and fix it, use some of the Right Stuff on the end walls. That stuff works really well!

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                        • #13
                          The instruction manual ( even though it's a Chevy in the pictures ) shows how to properly install the intake manifold.
                          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

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                          • #14
                            Just got everything put back together, and turns out there was no sealant around the intake ports, causing my oil consumption and vacuum leak. Just took it for a drive and its still going a little lean when I accelerate and it's now a hair more lean than it was before while cruising and accelerating when warm (around 14-15 AFR). Is this about normal? I think the issues when cold can be taken care of with the cold start enrichment, I dialed that back after we sealed everything up.

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