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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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    Got up this morning and noticed now the fuel filter is holding gas just find almost full. I guess I can get a little jug and disconnect the line to make sure that the gas is pumping from the fuel pump also itself. Good thing is at least the gas in the fuel filter is not draining back like it was before. Ran it today about 2 miles and had no stalling issues and fuel filter stayed full. Will keep observing it, Thank You
     
  2. Scrounge

    Scrounge Well-Known Member

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    According to his signature, it's a 225, which probably has a 1-barrel carb.

    My '84 D100 had a return-line fuel filter and a 2-bbl carb. But most of those I've seen through the '70s had the older type fuel filter, 5/16 line on the V8 engines.

    Was this with the gas cap on or off? And how much gas was in the tank? You may have altered something in the tank when you removed it. Maybe some dirt entered the tank when the sending unit was replaced, and that impeded the flow. The pump may be suspect and should be tested, but once your tank is near empty, you might want to remove the sending unit and inspect it.
     
  3. dana44

    Ad-Free Member

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    Yeah, engines do not vapor lock within the first five to ten minutes of driving, so that isn't the issue.

    How long has the new fuel pump been on? If it had been working before but just started having an issue, backwards lines isn't a problem.

    Have you removed the supply line and checked, when the filter is empty, if the fuel line from the gas tank is letting fuel pass through the line? Might be some junk in the tank blocking the pickup sock.

    Lastly would be a basic vapor lock if there is a return line or charcoal canister and to see if this is being an issue, crack the gas cap and drive around, see if the problem goes away (if it hasn't already according to your last post).
     
  4. 68RT

    68RT Well-Known Member

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    Blockage like the sock on the intake of the fuel tank line?
     
  5. dana44

    Ad-Free Member

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    Very possible. Have to narrow the sucking problem down a little bit to make sure. Disconnect the hose right at the fuel tank and put it in a gas can to see if the fuel pump sucks gas from there. This will tell you if it is the line to the fuel pump from the tank or the pump itself. If this works and she stays running, problem is at the tank. If you have vapor line, verify it is good by blowing through it and sucking through it (carefully) so make sure it isn't plugged. Does she have the charcoal canister or a tank vent tube? Canisters can become plugged and cause a vacuum that prevents fuel from being sucked and do this. If all these things check out, then pull the sending unit and pick-up out of the tank and check the sock. The charcoal canister lines haven't been switched around, have they? I think they are marked, or there should be a sticker that shows the routing somewhere under the hood.
     
  6. ImperialCrown

    Level III Supporter

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    Looking inside a 40 year-old gas tank can be frightening. Your arm may be too big to get inside and wipe it down. You might be able to boil it out if the seams and sheetmetal is still strong enough not to leak afterwards.
    I have had socks and filters clog from tank debris.
     
  7. AHBGuru

    AHBGuru Active Member

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    Canisters, believe it or not, are still available for most M-bodies, as is the surge valve, and the roll-over valve. Mechanical pumps have been absolutely horrible in quality, but OEM was Carter through '89, so one's odds are slightly better with the good old 519 pump.

    One restoration, and only one, I went with repop fuel lines. Very high dollar, all very nice and pretty, but just like the crap exhausts these cars had, you can have them bent up far cheaper and reroute them to cooler and safer locations, too.

    Excellent advice regarding the 1/4" return line, which tends to rust and clog up, as does the nylon pickup tube sock. Another F/M/J anomoly is the fuel line likes to crack or leak in the worst places, which will cause the pump to draw air.

    The last 3 M-body squads I restored, I used the vapor-lock kit with the Quadrajet. Never a problem. You can approximate the kit with a low-pressure (7 psi) electric pump near the tank to the Carter pump up front. The Qjet has that spring-loaded inlet filter which acts much like a pressure regulator (which is why the kit for the TQ *had* one), and works very well set up that way. Especially nice in temp extremes.
     
  8. 77LeBaron

    77LeBaron Member

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    I do not think fuel can be boiling , it is more likely bubbling which means air is being drawn into the system. Sounds like the problem was solved in your last post , you ran the car 45 minutes with no problem what has happened since your last post ?
     

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