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Super CONFUSING fuel supply problem.....

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Can Can, Jan 18, 2002.

  1. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Some of you may be familiar with a hard start porblem with my 84K5. For those of you that aren't, here's the quick details. When I fire up the truck in the morning, it stalls out after a couple of seconds. After it dies, the truck will fire again and jump to high idle with one more trun of the key.

    For the last week, however, the truck has refused to start again after the first false start. I have determined that to get it to fire again I have to prime the carb with a 1/4 cup of raw gas.

    This led me to believe I wasn't getting fuel from the fuel pump. I have a Carter electric pump instead of the mech. pump, so I disconnected the fuel line at the carb to see if maybe the pump was shot, but that isn'y the case. I got about a cup of fuel out of the fuel line with the pump running for less than a second.

    So here's the mystery: After the first false start, with the fuel pump running, I can't get fuel into the carb no matter how many times I pump the gas pedal!!!!! Is my float stuck in the off position? I've heard of the float getting stuck in the on position and causing flooding, but never the reverse.

    WHY AREN'T I GETTING FUEL AT THE CARB?????

    Sorry for the long winded question, but I really need your guys help on this one.......



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  2. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    Can you hear the pump running? What about leaving the key on (without starting) for awhile to fill the bowl.....?

    Check ALL clamps from one end to the other for looseness.

    Check all filters (and look for other in-line filters that you may have missed).
    Pumps can go bad but still flow under no pressure.

    Maybe check the in-tank pickup.



    Prolly not a filter problem since it will eventually run..... Bowl is draining.... And/or pump is weak.

    I'll think on it.


    Dave

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  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Well the needle and seat under the float bowl act like a tap for the fuel delivery. When the float reaches maximum hieght the needle is pushed into the seat sealing the carb off from getting more fuel until the float drops some. Maybe your carb has that leaking down situation we were discussing and also a sticky needle and seat assembly...

    From the problems you've been having I'd say a good rebuild would be in order. The kits are cheap and it's not that bad a job as long as the throttle shaft bushings are OK.

    Rene

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  4. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Thanks Dave......

    Pump is definitely running. Not only can I hear it, it pushes lots of fuel when the fuel line is disconnected. I may have to install a pressure gauge to see what the output is when the fuel line is connected though.

    The in-tank filter makes sense......maybe it's worth a look.

    I guess the first thing to do is to make sure I'm getting the pressure I need....



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  5. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    And I like what your fellow Canadian said (as usual).



    Dave

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  6. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Refresh me on the leak down situation again, Rene..... Are you saying that the carb won't let any more fuel in because the float might be sticking in the "full" position and tricking the needle and seat into thinking it doesn't need any more fuel?

    For the record, all the fuel lines and filters are in good shape. I checked those first in case the problem lied there.



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  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    <blockquote><font class="small">In reply to:</font><hr>

    Are you saying that the carb won't let any more fuel in because the float might be sticking in the "full" position and tricking the needle and seat into thinking it doesn't need any more fuel?

    <hr></blockquote>

    Yeah, thats the line I was thinking along. Over the years carbs get all 'gummy' inside. That could be enough to hang up the needle and seat...that's my theory anyways.

    Rene

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  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    To add to Rene's thoughts, maybe the accelerator pump has come appart. I have had the rubber seal pop off before and then you get no prime up when you set the choke. It will give a slight dribble just like you described to me. Another symptom is a bog when you get on the gas hard.
    Also while you may get fuel from the pump with no resistance maybe the resistance from the needle is enough that the pump can't over come it. Fuel pressure gage will diagnose that. Possible that you got some water contamination in the carb. It might be sitting in the area under the jets and freezing, effectivly blocking the flow of fuel to the main jets. Once a little heat gets to it then it is letting fuel get through. The base of that carb warms up pretty quick. There is an exhaust cross over passage that gets that carbed warmed up to help with cold weather.
    If you can positively rule out fuel pressure problems and ignigtion problems then I think it's time to go to the local parts store and get a rebuild kit and a can of carb soak.
    And while I have mentioned it....poor spark voltage can give you start up problems when cold that are hidden once it reaches operating temps so don't discount that. Fouled plugs, bad wires, coil problems, modual problems can all cause a problem. Need as much spark at start up as possible to handle the rich mix.

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