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Fuel pump and other wiring issues

Discussion in 'Tech Discussion' started by leviwatson, Jan 13, 2020.

  1. leviwatson

    leviwatson Junior Member

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    I'm working on a 84 k1500, and I have a 350 in it. At the end of the swap, but I'm struggling on the wiring side. There's a few different issues I'm having.

    1 - My junction block wiring. I can't find a diagram I can make sense of for this junction block. The drivers side post has a couple wires on it, but currently I don't have anything hooked up to the other side. What goes there?

    2 - I'm pretty sure I have some issue with the tank fuel pump wiring, since I don't have any fuel getting to the mechanical pump on the engine. Where would I find the wiring (in the engine bay?) for the pump?

    3 - I have one constant hot wire coming off the bulkhead wiring, but I don't know where it goes, any suggestions?

    Thanks for the help!
     
  2. Dougnsalem

    Dougnsalem Full Access Member

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    OMG. I better just leave right now. Can someone please help him out.
     
  3. Honky Kong jr

    Honky Kong jr Super Sarcastic Man

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    I’m confused......wiring diagrams are virtually everywhere. What swap did you do that there is a fuel pump in the tank and a mechanical at the engine?
     
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  4. Frankenchevy

    Frankenchevy Supporting Member Supporting Member

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    1-arrange the wire eyelets however makes sense. You should have continuity between the posts.

    2-unless you converted to efi, you won’t have an in tank pump. The mech pump may be bad or the lobe may be flat or it may be taking a while to catch a prime for whatever reason. Also, check for blockages in the line.

    3-it may be coming from the positive battery terminal.
     
  5. bucket

    bucket Super Moderator Staff Member

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    Pictures would help too. Specifically of the junction block.
     
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  6. leviwatson

    leviwatson Junior Member

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    Lol I feel similar tbh
     
  7. leviwatson

    leviwatson Junior Member

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    ok, so I was confused about that I guess, I thought that there was a pump in the tank and an additional one on the block. That not being the case clears up some confusion hah. Wiring diagrams are everywhere, I just don't really know how to read them well.
     
  8. leviwatson

    leviwatson Junior Member

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    Ok, thanks for the clarification, I wasn't thinking I had a pump in the tank, and then someone told me I did so that's what I went with. When I pulled the other engine (305) the pump worked. I can get a new one for pretty cheap, but I'm curious what the lobe is. I cranked for a long while, with no fuel coming through. I'll test the pump and see if it needs replaced.

    The hot wire is coming from the bulkhead wiring, I just didn't know of anything that needed power constantly.
     
  9. leviwatson

    leviwatson Junior Member

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    I will take some better ones and post them up.
     
  10. Frankenchevy

    Frankenchevy Supporting Member Supporting Member

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    What engine did you replace the 305 with?

    You’ll have 12v going into the cab. The line side of certain switches will have 12v present such as your light switch and ignition switch. You can check around on your fuse panel to explore what some of these circuits may be.
     
  11. leviwatson

    leviwatson Junior Member

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    I am putting a 350 it in it... Bought it used off craigslist and can't remember what it came out of. Getting in a little over my head with all the work haha, but I'm all for learning about it and I'm having a good time working on it. Thanks for the info.
     
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  12. bucket

    bucket Super Moderator Staff Member

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    If it's a very late 350, the cam might not have the lobe that operates the pump. Do you know if the engine has roller lifters? That would be a sign that it's a later block.

    Also, sometimes the average mechanical pump isn't strong enough to prime the fuel system at cranking speeds. It's best to fill the carb with fuel through the bowl vent, then start the engine. If it fires off and runs, the pump should continue to supply the carb with fuel.
     
  13. leviwatson

    leviwatson Junior Member

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    I think it's a late 70's 350. It came with a mech pump on it. Ok, that makes sense. I'll give that a shot. Thanks!
     
  14. chengny

    chengny Full Access Member

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    If the new engine uses a carburated fuel system - with a mechanical fuel pump - the wiring required to make it run is really simple. But before you get into the wiring, you need to confirm an adequate fuel supply into and out of the carburetor along with a proper spark. Do it like this:

    1. Release the supply line from the pump at the carb inlet and separate

    Copy of HPIM2351.jpg

    2. Attach a rubber hose to the end of the steel tubing

    3. Lead the other end of the hose to a container (12 oz. beer bottle is fine)

    4. Disable the ignition system by disconnecting the power to the coil primary. This will prevent a fire.

    Copy of HPIM1247.jpg

    5. While you hold the rubber hose in the container, have an assistant crank the engine.

    Fuel pump should supply 1/2 pint (8 oz.) or more in 15 seconds.



    If fuel supply to the carburetor proves sufficient, reconnect the power to the coil primary.

    The next check is that the carb is supplying fuel to the cylinders.

    1. Get a can of ether (starting fluid).

    2. Then while your assistant cranks the motor over, shoot a few short blasts of starting fluid directly down the carburetor throat.

    3. If the engine fires up, and then quickly dies out, it would suggest that the carb is not supplying gas to the cylinders.

    4. If it doesn't even kick over, that would point to a problem with the ignition system (i.e. a lack of spark)
     
  15. Honky Kong jr

    Honky Kong jr Super Sarcastic Man

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    Informative as always.:happy160:
     
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