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Thread: 1977 m880 no fuel pressure

  1. #1
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    Default 1977 m880 no fuel pressure

    Sooo this might be a long post but bare with me.

    I have a 1977 m880. Iam currently rebuilding the engine(just getting parts together) with my cam with lifters, intake manifold, timing chain and gears and 4 barrel carb. But first i decided to drop the gas tank and clean it out.

    All went well and i cleaned it out but i couldn't get the fuel sending unit out even after using a impact screwdriver so i left it alone. Reinstalled the tank and put about 8 gallons of fuel in and my truck started(using fuel that was already in the carb) It ran for about a min but i noticed no fuel was being pumped through the fuel filter and it cut off.

    The fuel gadge works, I put a new fuel pump in i had laying around. But still no fuel going to carb. My question is could i have damaged the fuel sending unit causing it to not send fuel to the pump?

    I just dropped the tank again and realized the line that send fuel to the pump was bone dry soo im guessing no fuel has even left the tank yet.

    Just to recap with some cliffs.

    1.cleaned out gas tank,fuel sending unit wouldn't come out
    2.reinstalled gas tank truck started with fuel left in carb
    3.Noticed as soon as it started no fuel was gushing through fuel filter.
    4.put in new pump and still no pressure
    5.dropped tank again and fuel lines were still dry

    What could be causing this?

    I plan on disconnecting the rubber hose and the fuel pump and routing it to a small jar with gas to see if the pump will suck gas through when cranking.

    Thanks for any help.

    engine december.jpg

    most updated pic of engine i have new ones soon

    16360_350024010365_737020365_10037065_3298644_n.jpg

    and all my parts

  2. #2
    4 Star General Elwenil's Avatar
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    It's possible that moving the tank around stirred up enough junk in the tank to plug the line. It's also possibly that the stock "sock" filter is still on the end of the pickup and is clogged. Another possibility is that the pickup tube rusted off inside the tank. Take an air line and blow out the lines from the tank to the carb and try to blow through the pickup. If the lines check out and the pickup is ok and you you can blow the sock off the end or blog the clog out you are good to go. If not you will probably have to pull the sending unit. Be aware that correct sending units are nearly impossible to find and when found are a pin to get the gauge to work correctly.
    ~Elwenil~
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    I went through my fuel system from the sending unit to the carb.

    Suggestion, using a hand operated vacuum pump and the brake bleeding attachment connect direct to the line that connects to the fuel pump, apply vacuum and hopefully some gas will show up in the bleeding trap jar. If you know that the vacuum pump works and no fuel, then internal tank connection, pickup tube and in tank repairs are in order.

    You might find a cracked section of rubber line allowing air in.

    Good luck.

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    Ok so update

    1. I discconected the rubber in line to the fuel pump and put some gas in a separate container and put the hose into it. When cranking the engine i got fuel pressure and it started right up.

    So that mean the fuel pump is ok and the cam is driving the pump arm just fine.

    Picture 001.jpg

    2. I Blew air into the out line from the gas tank(circled in the pick below) that send fuel to the pump. When blowing air in i heard air bubbles which should mean there is no clog in the sock.

    Picture 00.jpg

    There only other problem should be a leak in the lines correct?

    will test that tommorow.

    thanks again for the help.
    Last edited by digitalchi; 04-26-2010 at 20:49.

  5. #5
    4 Star General M543A2's Avatar
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    Try putting the end of an air gun in your tank filler sealed around best you can with a shop towel. Apply very light pressure and see if you get fuel through the line, or if you find it leaking out of a tube or pipe anywhere. Also, the rubber connector lines can get internal separation to where the inner lining collapses under vacuum, blocking flow.
    I had to take the screen off the end of the pickup in the tank on one truck I have because fuel varnish from deteriorated fuel had plugged it to the point it could not pass enough fuel.
    Regards Marti
    Warsaw, Indiana
    2 M-880 Pickups
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    1 M-139 5 Ton Bridge Truck
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    1 IHC T-9 SeaBees Dozer
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    OK sooo i fix it! turn outs there was a crack in the line right near the gas tank ever so small causing the pump to only suck air...instead of trying to find a line to replace it. I just found a longer rubber fuel line and routed it to the fuel sending unit.

    The only problem now is i currently have toe straps holding up the gas tank temp. because i had to cut off the old straps with a sawsall because they were so rusty.

    anyone know where i can find gas tank straps that will fit?? thanks

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