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Vapor Lock / Gas Issues

Discussion in 'F-J-M: Volare, Diplomat, etc, 1977-89' started by Mopar_Gods, Jul 30, 2017.

  1. Mopar_Gods

    Mopar_Gods Member

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    Took the 1977 Dodge Aspen 2 Door Coupe out last week got about 1 mile of the road and she shut down. I was able to get it off the road in a busy intersection thank god. Popped the hood and noticed that the clear fuel filter did not have any gas in it. Called the collectors insurance for a flat bed. Could not get it to pump gas cranked at least 15 times. Got home removed the fuel filter to see if blockage there was not any primed the carb it fired right up.

    Went to take the aspen out today pulled it outside so the gas fumes would not kill my lungs started it let it idle for a few minutes and noticed the fuel filter beginning to fill up but then I noticed it looked more like it was boiling in the bottom of the filter more then filling the filter up if my eyes are working correctly. Let it idle till the gas in the filter ran completely dry again. Removed the top hose of the filter manually poured gas in it again and the fuel in the fuel filter ran completely dry again after just a few minutes.

    The tank has a new fuel sending unit. The lines have all been replaced. The mechanical fuel pump has been replaced. The carb when the fuel filter does have gas in it when I move the choke manually I can see the jets on both spraying a nice solid stream of gas on both side. I have ran out of ideas. Any other feed back would be greatly appreciated she is aching to be driven more before the summer is over and my right foot needs sum throttle lol. Thank You
     
    #1 Mopar_Gods, Jul 30, 2017
    Last edited: Jul 30, 2017
  2. Mopar_Gods

    Mopar_Gods Member

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    Took the 1977 Dodge Aspen 2 Door Coupe out last week got about 1 mile of the road and she shut down. I was able to get it off the road in a busy intersection thank god. Popped the hood and noticed that the clear fuel filter did not have any gas in it. Called the collectors insurance for a flat bed. Could not get it to pump gas cranked at least 15 times. Got home removed the fuel filter to see if blockage there was not any primed the carb it fired right up.

    Went to take the aspen out today pulled it outside so the gas fumes would not kill my lungs started it let it idle for a few minutes and noticed the fuel filter beginning to fill up but then I noticed it looked more like it was boiling in the bottom of the filter more then filling the filter up if my eyes are working correctly. Let it idle till the gas in the filter ran completely dry again. Removed the top hose of the filter manually poured gas in it again and the fuel in the fuel filter ran completely dry again after just a few minutes.

    The tank has a new fuel sending unit. The lines have all been replaced. The mechanical fuel pump has been replaced. The carb when the fuel filter does have gas in it when I move the choke manually I can see the jets on both spraying a nice solid stream of gas on both side. I have ran out of ideas. Any other feed back would be greatly appreciated she is aching to be driven more before the summer is over and my right foot needs sum throttle lol. Thank You

    Sorry just noticed I also placed this in the restoration section just noticed. Please correct if it is issue.
     
  3. 68RT

    68RT Well-Known Member

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    Engine should not be hot enough to cause vapor lock under the stated conditions. However, I strongly suspect that you have a leak between the pickup tube in the tank and the fuel pump inlet. That can be hard to find as it could be a tiny hole in either the tubing or hose. Fuel pump seems to be pumping air based on your description. It is a poor air pump as it was designed to pump solid liquid.
     
  4. Mopar_Gods

    Mopar_Gods Member

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    So visible leaks? None that I can see anyways.
     
  5. Scrounge

    Scrounge Well-Known Member

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    I also preferred the clear plastic gas filters. Those I usually bought had an arrow on them pointing which way the gas should flow; the arrow should always point toward the carb. If yours has one, make sure it's pointing in the right direction.

    If you think it's vapor lock (and this time of year, it's possible), it's probably due to the ethanol in the gas. Here's a link describing some treatments to neutralize the ethanol:

    What is the Best Ethanol Fuel Treatment? (at http://www.fuelsystemguide.com/what-is-the-best-ethanol-fuel-treatment/ )

    You mentioned gas fumes -- is it leaking anywhere? If so, try to trace it with the engine running. Otherwise, you might start tracing backwards: take the hose off the other end of the filter to see if gas is coming out of the fuel pump. If not, remove the hose on the other side of the fuel pump to see if gas is coming out of the tank. It's possible that one of the parts you replaced needs replacing again. I had to replace a fuel pump on a '65 Monaco twice within a year.
     
  6. Mopar_Gods

    Mopar_Gods Member

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    Is facing up correctly took it off it isn't blocked matter of fact the filter is like a few weeks old if that. No it has always ran a little rich so I always pull it out of the garage instead of messing with it in a closed building. No I have looked from the tank all the way to the carb I see no leaks.
     
  7. AllanC

    AllanC Well-Known Member

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    Vapor lock typically occurs at slower driving speeds. The fuel picks up heat from the engine area and starts to evaporate / boil. The fuel pump can only push liquid, not vapor into the carburetor. The engine dies because of fuel starvation.

    If the engine is at ambient temperature then driving just 1 mile is not sufficient time for the fuel lines to absorb sufficient heat to cause vapor lock. However how are the fuel lines routed? Is the inlet line to the fuel pump close to an exhaust manifold? That might cause a problem.

    If you see the accelerator pump spraying fuel into the carburetor throat after a hot stall, then vapor lock is not the issue. Vapor lock causes no fuel, just vapor and there would be no liquid stream pushed by the accelerator pump.

    Another possibility is that you could be experiencing percolation in the carburetor. Heated fuel starts to vaporize in the carburetor bowl, push against the needle valve and flood the carburetor and intake manifold with excess gasoline. But again it takes some driving under high temperatures to cause this to happen.

    Do a Google search on gasoline vapor lock and percolation. You may find some helpful tips.
     
  8. ImperialCrown

    Level III Supporter

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    How old is the fuel pump? Are you sure that you're seeing boiling fuel and not air bubbles? Any leaks on the suction side of the fuel pump will also pull in air when operating.
    If the car sat and the pump was allowed to dry out and then restarted, the fuel pump could be failing.
     
  9. Mopar_Gods

    Mopar_Gods Member

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    To be perfectly honest I am not sure if I was seeing boiling or bubbles. The fuel pump is new and the cam lobe is coming in contact with the arm on the fuel pump I have checked it to make sure prior to this new issue. I try to drive it at least once a week. Thank You
     
  10. 68RT

    68RT Well-Known Member

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    This type of leak never is external. If there is a hole in the line above the tank level, it allows the fuel to drain back to the tank. When the pump draws fuel, it also draws air. Sometimes enough you can't get fuel at all. And the hose can do tla very similar thing.
     
    pt006 likes this.
  11. Mopar_Gods

    Mopar_Gods Member

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    I guess I will be installing a electric fuel pump was hoping not to half too, Would like to keep the mechanics of the vehicle original as possible. I do know this is not always possible. Had a few minutes to mess with it some more today. Cranked it today and noticed still no gas making it to the fuel filter even after cranking it over at least 20 times.

    So removed the gas cap disconnected the top rubber hose to the fuel filter manually filled the filter with fuel and of course it started right up then put the gas cap back on. Weird sat there and watched this vehicle for a good 45 minutes and fuel filter stayed full.

    In case I am wrong I am pretty sure if the mechanical pump was bad then surely the filter would of ran out of fuel before 45 minutes of the engine running even at just idle. Am still puzzled with it myself. Not sure if I am right but couldn't a gas cap with a bad seal cause to much suction to form and pull gas back to the tank from the fuel pump?. Just a thought I had.

    Before I forget I did not notice any air bubbles or boiling or any kind of suction or drainage from the fuel filter this time around just stayed full for 45 minutes. Went back out there to look to see if fuel has drained back down from filter and it still looks almost full damn thing driving me crazy here.
     
  12. pt006

    pt006 Active Member

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    The diaphram in the fuel pump might have a pinhole/leak in it, allowing air from crankcase to enter the suction side of the pump. I'd try a new mechanical pump first.
     
    Bob Lincoln likes this.
  13. ImperialCrown

    Level III Supporter

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    I have had the 'one-way' check valves in mechanical fuel pumps be intermittent. These were like getting the cars that got towed in to the shop, but then started right up.
     
  14. Rick Anderson

    Rick Anderson Well-Known Member

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    From the description, it sounds like you've just spliced a "universal" fuel filter into the line. Since the fuel is drawn/sucked through the filter before the pump, an undersized filter might create a problem as well, might be why you see the filter empty, even though fuel is getting to the carb for at least some time.

    No, I don't think its the most likely cause, but its one possibility to put on the list.

    Have you tried priming the carb and disconnecting the fuel hose to the carb and running it to a bucket. Starting the engine and observing the fuel flow out of the hose? It should be a steady solid stream of fuel coming out of the hose. Or if you can get a fuel pressure gauge, it should be 7-8PSI fuel pressure.

    Like IC said, its not that surprising for a fairly new fuel pump to go bad, if the vehicle is seldom driven.

    Finally, the mechanical drive of the fuel pump. Either plunger or cam eccentric, there could be unusual wear on the driving mechanism and cause the fuel pump lever to move far less than it should, resulting far lower fuel pressure than you need. I had this with a 440, that I rebuilt myself and must have had a bad plunger in the kit, the plunger wore down right away, and didn't push the fuel pump lever as much as it should. The low fuel pressure gave me very similar symptoms as what you're experiencing. Seldom driven vehicle, the engine is started more dry of oil than a more regular driven vehicle, and something like a plunger or eccentric for the fuel pump wearing much faster than expected is possible.
     
  15. chuzz

    chuzz Well-Known Member

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    I'm inclined to agree with Rick Anderson on the eccentric being worn. This is not an uncommon thing especially if this is a high mileage slant six engine. The idea of a pinhole in the fuel pump diaphragm is also possible, especially if it sat around in a warehouse on a shelf for several years. Maybe even the spring on the fuel pump plunger could be weak. IDK, I'm not a mechanic. Just trying to throw some ideas out there based on my experiences over the years. And like stated before, the routing of the fuel delivery line can sometimes be too close to the exhaust manifold. My dad used to put aluminum foil and clothes pins on the fuel line in his 48 Plymouth in the summer time. He swore that took care of the vapor lock problems he had with it.
     
  16. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    It sounds like he is using the factory configuration, with a clear plastic housing for the fuel filter, which was common back in the day, vs a metal housing where you can't see the fuel level or filter element. And it is between the fuel pump and the carb, not before the pump.
     
  17. AHBGuru

    AHBGuru Active Member

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    Lots of missing pieces here. What engine, what carb, what else was monkeyed with?

    Regardless, if this car has the 1/4" return line from fuel filter to the tank, blow the return line out with compressed air and get the correct 3-nipple filter on it.

    Next, depending on the carb, make sure you've got the correct baseplate gasket. Make sure your fuel line is routed away from hot parts (I used to cover them with slit 3/8" rubber fuel hose).

    Make sure the bowl vent is hooked up properly. Make sure the charcoal canister isn't plugged. Make sure the nylon sock (filter) at the end of the pickup on the sending unit isn't blocking flow.

    After all of that, and if you are in fact boiling the fuel, you could try a low-flow pusher electric pump, regulated to 7 psi. Mount it near the tank to simply push the fuel up to the mechanical pump.That's basically what the squads had from '86-89, although that factory field modification used an in-tank pump.
     
  18. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Slant-sixes don't have a return line from a fuel filter.
     
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  19. valiant67

    valiant67 Rich Corinthian Leather
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    They eventually got the third return line, especially in CA emission cars. I'm not sure of the time frame though.
     
  20. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    OK. My dad's 79 Aspen did not have one. Have never seen it outside of fuel injection.
     

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