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Vapor Lock

Discussion in 'Early CJ-5 and CJ-6 Tech' started by Brian Rowland, Apr 29, 2019.

  1. Apr 29, 2019
    Brian Rowland

    Brian Rowland New Member

    Denver
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    Mar 25, 2019
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    Hey Everybody,
    So happy to find this site.
    I have a stock and original Cj5 that my father bought new in 1969. Dauntless V6. I have a new fuel pump with the return line. Heat shield.
    I looked at the forums but didn't find my particular case and I don't remember this happening when I was young and we wheeled a lot at altitude here in Colorado.
    What happens is, the jeep runs great until we hit around 11,000 feet and then it vapor locks. I have poured water on the pump when we stop and it runs great for awhile then starts again. This will then keep even at low altitude once it starts but when we get on the highway it goes away.
    Does gas today vapor lock easier? Is the old engine running hotter? Any thoughts on more shielding, insulating, remedies?
    TIA

    Brian Rowland, Mar 25, 2019Report
     
  2. Apr 29, 2019
    TIm E

    TIm E Member Sponsor 2019 Sponsor

    NW Arkansas
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    I would maybe start by looking at where the fuel lines come from the tank to the fuel pump underneath the driver's side. Pretty tight in there and they pass fairly close to the exhaust. If the fuel lines are original, they are poly lines. Likely time to replace as I bumped one once in a 69 ever so slightly and it just broke. Another test might be to get some non-ethanol fuel, you can usually find a place that sells it. Workman's Truck Stops and Conoco stations here have it.

    It could be something else as well, perhaps some of the high-altitude guys will chime in with ideas.
     
    65CJ5 SRD likes this.
  3. Apr 29, 2019
    colojeepguy

    colojeepguy Colorado Springs Sponsor 2019 Sponsor

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    Yes.
    Is your return line hooked up?
     
    Bowbender likes this.
  4. Apr 29, 2019
    mortten

    mortten I can’t put my finger on it

    Peninsula, Ohio
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    Mine used to lock all the time with the return line disconnected. Hooked it up never happened again
     
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  5. Apr 29, 2019
    Brian Rowland

    Brian Rowland New Member

    Denver
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    Yes, return line hooked up.
     
  6. Apr 29, 2019
    colojeepguy

    colojeepguy Colorado Springs Sponsor 2019 Sponsor

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    They aren't routed that way on a 69
     
  7. Apr 29, 2019
    PeteL

    PeteL Member Sponsor 2019 Sponsor

    Hills of NH
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    Antique car guys will go to an in-tank fuel pump, or mount an external one below the tank level, so as it "pushes" fuel rather than pulling it. Any suction increases vapor formation.
     
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  8. Apr 30, 2019
    colojeepguy

    colojeepguy Colorado Springs Sponsor 2019 Sponsor

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    My 70 has the stock fuel system and I regularly go Jeeping at high elevation. I've never had a vapor lock.
    I would check the fuel pump pressure, make sure it's putting out what it's supposed to. Also, if you can find a gas station with ethanol free gas, that's worth a try as well...my Jeep runs better on real gas.
     
    65CJ5 SRD likes this.
  9. Apr 30, 2019
    Warloch

    Warloch Did you say Flattie??? Staff Member Sponsor

    Falcon, CO
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    Had a similar issue years ago with one of my swaps. I had developed a small exhaust leak and it was heating the line from the pump to the carb. Ended up putting some wrap, heat deflector, and exhaust gasket in before I was done. It went away in the end, but only stumbled on the exhaust leak while I was doing some other work.

    Why it only did it at higher altitude I chalked up to the lower boiling point and usually going slower under load while crawling. Your mileage may vary with this answer :)
     
    65CJ5 SRD, Brian Rowland and fhoehle like this.
  10. Apr 30, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    Hellion and FinoCJ like this.
  11. Apr 30, 2019
    Brian Rowland

    Brian Rowland New Member

    Denver
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    Wow, thanks. There are a couple close actually. There has been so much snow here this winter it will be July before I can go up high but will try this for sure.
     
    ITLKSEZ likes this.
  12. Apr 30, 2019
    Brian Rowland

    Brian Rowland New Member

    Denver
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    Interesting. Thanks.
     
  13. Sep 30, 2019
    Brian Rowland

    Brian Rowland New Member

    Denver
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    Hi everybody, just a quick update, new pump, filter, wrapped exhaust, good gas, thanks for all the tips. They helped a lot! here is a pic from this summer at about 11,500 feet and we went even higher with no problems. Thanks.
     

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  14. Sep 30, 2019
    colojeepguy

    colojeepguy Colorado Springs Sponsor 2019 Sponsor

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    Great pictures! Where is that?
     
  15. Sep 30, 2019
    Brian Rowland

    Brian Rowland New Member

    Denver
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    Kingston Peak near Idaho Springs Colorado
     
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  16. Sep 30, 2019
    tomasinator

    tomasinator Member

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    I gotta move to Colorado!
     
  17. Oct 1, 2019
    Brian Rowland

    Brian Rowland New Member

    Denver
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    Yes, it is pretty amazing.
     
  18. Oct 1, 2019
    duffer

    duffer Rodent Power Sponsor 2019 Sponsor

    Bozeman, MT
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    This! If you have a pump that isn't up to spec and/or a partial restriction in the line to the tank they will enhance the prospects of vapor lock. Those would be addition to excess fuel heating.

    I never had a problem with my CJ 5 at high elevation either.
     
  19. Oct 7, 2019
    65CJ5 SRD

    65CJ5 SRD Member

    NM
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    Re: Restriction in line...had something happen recently that I'm still shaking my head over...

    Went out to use the Jeep a few weeks ago and it wouldn't start. It was fine when I parked it a couple days earlier. But that day no amount of cranking would work and normally it starts instantly now with one hit of the key and no cranking. I figure it's either spark or fuel.

    So, I looked at everything and it all looked fine; lines tight, no leaks, all looked OK. So I put a bit of gas into the carb and it started instantly then died. So I figure it's either the new electric fuel pump or a blockage. Pump was chattering away like normal so I'm thinking blockage.

    I took the hose off the input to the carb. Carb inlet was clear. So I set it up so I could run the fuel pump from the engine compartment. I took a glass cup I keep out there and ran the pump. Good fuel flow, nothing wrong there, and I'm just about to shut it off when...BLOOP. WHAT the heck was THAT? There's something floating in the gas. At first I thought it was big piece of rust or a flake of paint. I looked at it close up and it's a freaking cockroach, just the size of the fuel line ID. I stood there staring at it for literally 10-15 seconds in pure disbelief. So I fished him out, reconnected everything and it started instantly and ran fine as before.

    Of course I'm wondering how the heck he/she/it got in there. There's a fuel filter after the fuel pump and if it came from the tank I'd expect it would have been stopped there. My guess is it was in the fuel regulator which I needed for the new electric fuel pump. That regulator was essentially new but had been stored in a box for years before I took 2 days of tearing the garage apart to find it. It never occurred to me to look inside it for bugs.

    I'm just glad that a) it was easy to find and fix, and b) my diagnostic process seemed to work (this time!).
     
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  20. Oct 11, 2019
    mortten

    mortten I can’t put my finger on it

    Peninsula, Ohio
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    (y) Mud daubers usually get me.
     
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