Engine dies when hot, in gear

Small Block Mopar Engine

  1. Chedrick

    Chedrick Member

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    I’ve been on and off chasing gremlins for a few years now and haven’t been having much luck. I have a 74 duster with a 318/727, Edlebrock AVS 2 carb, performer intake, headers, edlebrock coil, summit distributor, and blue hi Rev ignition box. Previously it was hit and miss but it’s getting more consistent if it’s the same issue.
    The car will run fine for 20-30 mins then stall when stoped at light or stop sign. Shifting in neutral and revving seemed to help but after doing that the other day I couldn’t get it to stay running at all (fortunately in my driveway). Once it cooled down, fired right back up the next morning.

    Over the past few years I’ve changed the key switch out, bulkhead connector, coil, ballast resister, distributor, plugs, wires, ignition control module and carb.
    Yeah that’s a lot of shotgunning but it sat for over 10 years before so I figured it couldn’t hurt.

    Today I added a carb spacer with no change. I put a clear fuel filter in line and looks like the fuel is bubbling in the filter so I’ll try and new filter tomorrow and move it farther away from the engine.

    I’ve hooked up temporary wires to the coil and measured voltage at the ballast resister and + coil while it was having issues. Seems like the coil +voltage runs between 5-9 volts and the voltage at the resistor was generally 12-14v.

    Initially I thought it was electrical but I’m leaning towards fuel related now that I’ve seen the clear filter bubbling and being empty after it’s gotten hot and sat for a bit.

    Just wanted to see if anyone else had ideas since I have a couple days off and hope to play with it this weekend. Will get new rubber lines and move a metal filter away from the engine in the morning. Thanks for any insight
     
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    • justinp61

      justinp61 Well-Known Member

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      How close is the fuel line to the header where it runs along the frame rail on the passenger's side? Does it do it in cool weather too?
       
    • Dana67Dart

      Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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      The "empty" filter is actually full of pressurized fuel vapors.

      Have you checked your fuel pump? ( Doubt that is the issue)

      Have you checked your fuel pressure? (Cold and hot and when having issues)

      You can try an easy thing.

      Go to www.pure-gas.org and see if there is a station near enough to you that sells alcohol free gas.

      Run your tank down to 1/8 tank and fill with alcohol free gas.

      See if you still have the issues.


      This is my dart on standard pump gas with typical alcohol.

      https://photos.app.goo.gl/QMB1A18RfUEz4Hgp9


      During this test. The pressure between the filter and the carb stayed at about 5 to 6 till the filter was fully empty, the pressure lowered to about 3 then the engine rpm started to drop, then the inrush of fuel and the rpm picked back up. This would happen when ideling after a 45 minute around town drive.

      On really hot days (90+ deg) if I sat in a drive through lane then hit the road. Under normal acceleration the engine would loose power, I would let off the gas the engine would return and I could keep driving.

      ALL of these things went away when I started using alcohol free gas, NO OTHER CHANGES!

      don't know if it will solve your problem but it is easy to try.
       
    • Chedrick

      Chedrick Member

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      Thanks for the thoughts. The filter is almost vertical sitting on the front of the engine between the pump and the carb, kinda beside the alternator. Closer to the block than it probably should be. I did check fuel pressure once when it was cold and it was around 6psi.

      I had the same thought about the alcohol free gas and considered filling up with avgas but figured that wouldn’t help me after I ran out and needed to refill. Maybe I’ll try and keep an eye out for the stations listed on that website. There’s gotta be a way to keep this thing running on regular pump gas! Maybe a newer Hemi swap is the answer
       
    • Dana67Dart

      Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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      My suggestion is mostly to prove it is a fuel issue.

      There are ways with a return hose, to bleed off the vapors keeping fuel to the carb.
      Or pressure regulators etc.
       
    • Chedrick

      Chedrick Member

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      Yeah that’s a good point. I need to confirm that is the issue then I can figure out a plan to fix it.
       
    • krazykuda

      krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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      "Engine dies when hot, in gear"

      Then don't put it in gear when it's hot...


      Captain Obvious A01.png
       
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      • Ironracer

        Ironracer Gearhead

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        My 74 Duster, after I pulled the 318,and slammed the 340 in, would idle I the driveway half a day, would run the block... when trying to drive er home ( had 2 "places") she'd shut down. Sometimes, after cooling, she'd fire up. Changed fuel pump, coil (have had a coil do that same tho) all kinda cussing, ect. Probably didn't NEED A new gas tank, but when I pulled the sender, and the inside looked like some kinda cavern in the mountains, I nailed it. Took er out, drove all around the woods in the hood here, I matted it (225/60/15) blew em off and spun er round! Never again had an issue. Had a 63 Dart I chased that on too. I could disconnect the hard line from the engine bay, and blow backwards, and hear it like a bong, fucker would die. Think it was the rubber line from sender to the metal hard line. Car sat for almost 8 years at my Grandparents. Got it rolling back from Gainesville to Tampa, then back and forth to Orlando for work, cure was a long rubber line to a gas can in the cab. DO NOT REPEAT THAT. I was a crazy kid.....
         
      • 66Valiant528

        66Valiant528 Well-Known Member

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        It's easy and cheap enough to get a filter with a vapor nipple on it. 85 Omni 2.2 5/16 though and run a return like to the tank. There's usually an unused nipple on the pick up assy. Give it a try. Two little pieces of rubber hose and hard line.
        Your high performance blue module is suspect as well. Had a friend with a similar issue. I gave him an old SMP LX101 I had in the garage.....all better.
         
      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        Easy diagnostic trick. Line up as many wooden clothespins on the fuel line as you can fit on it. Start it up and drive it. If it doesn't stall then it's the fuel turning to vapor and the clothespins are acting like a heat sink and preventing it. You'll want to insulate or reroute the fuel line.
         
      • Chedrick

        Chedrick Member

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        Thanks for all the thoughts;!Messed with it some today. Moved the filter off the block some, siphoned the fuel and put in ethanol free, blew out the vent line and also tried running it with the cap off after it started acting up with no luck. The filter was still mostly full of vapors and bubbly after it got hot. I hooked a fuel gauge up inline and it was reading 7 psi at idle. Edlebrock calls for 6.5max, I don’t imagine that .5 psi is the culprit. Tomorrow I’m going to try and wrap the metal fuel line beside the headers with a rubber hose or make a heat shield for it. I have swapped the blue ignition box for an old orange one I had laying around and nothing seems to change there
         
      • Bodyperson

        Bodyperson Pedal to the metal FABO Gold Member

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        Kind of grasping at straws here as I don’t really think this is the solution but… the wrong torque converter can drag the engine down like this. Could be more than one condition too.
         
      • Babyblue66

        Babyblue66 Cool dude

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        My Barracuda would do that when it got hot with an edelbrock carb. With a holley it's never happened.
        Also I had 2 edelbrock 600 on a dual quad 440. It would chug in traffic and shut down halfway down the drag strip. Put on a tunnel ram with same carbs, no issue. Put on a holley single 4 barrel intake. No issues.
         
      • CRUZE 418

        CRUZE 418 FABO Gold Member FABO Gold Member

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        I am a doubting Thomas on the insulation or against the engine with the filter. If that was it, we all would have the same problem. Sorry that I do not have any other suggestions. Keep looking, there is a simple answer here, but simple answers can be hard to find.
        Best of luck.
         
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        • Chedrick

          Chedrick Member

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          Im starting to think this may be the case….trying to remember the exact time frame on things but I think this shutting down thing came up after the carb. I’ve been sorting issues out over the past few years but the 2 summers before covid we drove 2 hours each way to Mopar nats so at least the car was drivable at that point. I’m afraid to take it across town right now. Hate to throw a Holley at it and find out that’s not the fix but I’m lost otherwise
           
        • AJ/FormS

          AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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          Since you have fuel in the filter, and pressure, the pump is fine. Fuel vapor bubbles will not form at pressure. So the question is, what are the bubbles?
          My guess is that the pump is sucking air.
          There is a hose-jumper at EACH end of the hard line.
          The front one usually leaks if it is not tight.
          But the back one is above the liquid in the tank, so it does NOT leak. But the pump can easily suck air there. Replace the hose, and reuse the factory spring clamps. If you do not have the factory clamps, and are forced to use gear-clamps, you have to use two of them per side and stagger the screws 180*. And you have to be careful to NOT overtighten them, because they will bunch the hose up, and create an airspace under the screw-box. You probably won't see it, but the pump will love it, on account of sucking air is easier than sucking gas.

          Now; you can prove that the pump is sucking air by doing a fuel volume test. Just run the pressure side into a clear glass 2qt pickle jar or equivalent, with the line submerged in the fuel. Then start the car and let it idle on the gas that is in the carb. If you see bubbles, there you have it.
          While yur doing this, your pump should supply about 1qt in a minute or less at 500rpm.

          If the pump still bubbles after you replace the rear jumper, and the fuel line does not have a leak anywhere; Then;
          your fuel-line may be severely restricted . When fuel under suction has to pass thru a restriction, this action often produces bubbles. What I have found in the past is that water collects in the lowest point of your fuel line, and rusts the line from the inside out. The rust forms a restriction and a resulting soft-spot. My trusty pliers finds that spot for me in short order. Then I just cut it out and fix it or replace the whole line.
           
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          • furrystump

            furrystump Well-Known Member

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            I run two pumps. A big mechanical and a Holly red in the back. Originally I was nervous about filling the engine with fuel if the diaphragm in the mechanical ruptures, but I have been running it like that for 10 years. A bit overkill on a street car, but there are several advantages. The first is if the car sits for any length of time the fuel in the carb evaporates out and you probably need to crank it FOREVER to start it. The electric pump will fill the carb in a couple of seconds. Another is REALLY stable fuel supply and my car will run with the electric off. So if the holley pumps dies I can still get it home. It won’t rev over 4000 rpm, but it will run. Finally to your issue, it keeps the fuel under pressure from the tank forward. A mechanical pump lowers the pressure in the line from the tank up to the pump inlet. Making the fuel boil at a lower temp. The electric keeps the fuel pressure at 5-6 lbs, raising the boiling point. The down sides are a bit complex install and noisy. Make sure your fuel pressure gauge isn’t a liquid filled gauge. They go nuts with changes in temp.
             
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