Fuel problem

[MitchThor14]

Hello everybody

I have a 1984 C20 and when i try to start it it dies right away. It only starts if i pour fuel down the carb because it is not getting fuel. I have a brand new fuel pump, the lines are clear and i have cleaned out the tank and the sock on the spending unit is clear. Im not sure why it is not getting fuel so if anybody has some answers that would be great.

Thanks!

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[Pike1915]

Sounds like either the lines are backwards or wiring might be backwards..

[blazer74]

Quadrajet? Fuel filter in the carb changed?

[MitchThor14]

Quadrajet? Fuel filter in the carb changed?

Yes its the quadrajet and no i havent changed the filter but the fuel isnt even getting to the carb


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[MitchThor14]

Sounds like either the lines are backwards or wiring might be backwards..

How would the lines be backwards? And wiring for what?

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[Pike1915]

Did you put a new fuel pump in or did you buy the truck with a new fuel pump?  Sometimes people forget that the black wire is actually the positive and red is the negetive..

[bd]

Hello everybody

I have a 1984 C20 and when i try to start it it dies right away. It only starts if i pour fuel down the carb because it is not getting fuel. I have a brand new fuel pump, the lines are clear and i have cleaned out the tank and the sock on the spending unit is clear. Im not sure why it is not getting fuel so if anybody has some answers that would be great.

Thanks!

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What's the history on the fuel pump - why is it new?  Did the symptoms develop before or after replacing the pump?  Does loosening or removing the fuel tank cap make any difference?

Pick up a pressure-vacuum gauge (such as imaged below) and connect it to the 3/8" nipple on the fuel pump that normally connects to the tank.  Crank the engine for 20+ seconds and measure how much vacuum the new pump draws.  When stabbing the new pump, the installer may have missed the push rod with the pump arm so that the rod and arm are side-by-side instead of end-to-end.

[MitchThor14]

Hello everybody

I have a 1984 C20 and when i try to start it it dies right away. It only starts if i pour fuel down the carb because it is not getting fuel. I have a brand new fuel pump, the lines are clear and i have cleaned out the tank and the sock on the spending unit is clear. Im not sure why it is not getting fuel so if anybody has some answers that would be great.

Thanks!

Sent from my LG-H636 using Tapatalk

What's the history on the fuel pump - why is it new?  Did the symptoms develop before or after replacing the pump?  Does loosening or removing the fuel tank cap make any difference?

Pick up a pressure-vacuum gauge (such as imaged below) and connect it to the 3/8" nipple on the fuel pump that normally connects to the tank.  Crank the engine for 20+ seconds and measure how much vacuum the new pump draws.  When stabbing the new pump, the installer may have missed the push rod with the pump arm so that the rod and arm are side-by-side instead of end-to-end.

It was doing it before i changed the pump as well. I will check tomorrow with the gas cap open and if the pump was installed incorrectly. Do i have to prime the pump in any way after I have had all the lines off? Thanks for the reply!

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[blazer74]

No priming needed,

Check  your rubber hoses from the tank sender to the metal lines and the short pieces between the metal lines. 

The rubber can become restricted when they get old.

The bigger line is the fuel feed 3/8. The 5/16 line is the vapor canister and runs to the drivers side.
Pump outlet is hard lined to carb.
Pretty hard to mix them up.

Do the pump test like bd suggested.

Make sure you can draw fuel from the tank to the pump.

[bd]

I surmised from your initial post that you already inspected/replaced the fuel hoses using clear lines.  If that was incorrect, then checking the hoses as blazer74 recommended is fundamental to the tasks I suggested. 

Mechanical fuel pumps are self-priming as long as internal check valves seal as they should.  If you intend to remove the fuel pump again, you can have an assistant bump the starter two complete engine revolutions while you hold the pushrod against the camshaft and watch how far the pushrod travels in and out.  IIRC, the pushrod should travel proud of 5/16".  But, be careful!  Disconnect the primary power lead from the distributor cap to ensure the engine cannot start, avoid entanglement with the fan belts and pulleys, and make sure you don't trap your finger between the end of the pushrod and the fuel pump adapter plate or you'll risk serious injury.

Referring to the attached image, the silver bolt that protrudes from the front of the block threads into a hole that is drilled through into the fuel pump pushrod bore.  The hole is there so that a "long" bolt can be temporarily inserted and lightly retain the pushrod in the up position to help facilitate fuel pump replacement.  Any bolt threaded into that hole from the factory is surprisingly "short," penetrating no deeper than ~3/8" - 7/16".  A bolt penetrating that particular hole any deeper will bind the pushrod.  Under the circumstances, it would be prudent to verify that someone did not previously thread a 'long' bolt into this hole and inadvertently lock the pushrod in its extended position.  Be advised that the hole requires a bolt to seal against "mystery" oil leaks.

[Irish_Alley]

im sure bd is spot on about the fuel pump but you never did mention if its mechanical or electric

[MitchThor14]

I surmised from your initial post that you already inspected/replaced the fuel hoses using clear lines.  If that was incorrect, then checking the hoses as blazer74 recommended is fundamental to the tasks I suggested. 

Mechanical fuel pumps are self-priming as long as internal check valves seal as they should.  If you intend to remove the fuel pump again, you can have an assistant bump the starter two complete engine revolutions while you hold the pushrod against the camshaft and watch how far the pushrod travels in and out.  IIRC, the pushrod should travel proud of 5/16".  But, be careful!  Disconnect the primary power lead from the distributor cap to ensure the engine cannot start, avoid entanglement with the fan belts and pulleys, and make sure you don't trap your finger between the end of the pushrod and the fuel pump adapter plate or you'll risk serious injury.

Referring to the attached image, the silver bolt that protrudes from the front of the block threads into a hole that is drilled through into the fuel pump pushrod bore.  The hole is there so that a "long" bolt can be temporarily inserted and lightly retain the pushrod in the up position to help facilitate fuel pump replacement.  Any bolt threaded into that hole from the factory is surprisingly "short," penetrating no deeper than ~3/8" - 7/16".  A bolt penetrating that particular hole any deeper will bind the pushrod.  Under the circumstances, it would be prudent to verify that someone did not previously thread a 'long' bolt into this hole and inadvertently lock the pushrod in its extended position.  Be advised that the hole requires a bolt to seal against "mystery" oil leaks.

The pushrod should be fine, and i don't think that there is a long bolt in there because my grandpa was the only other owner of the truck and the reason he parked it was because of bad valve seals not a fuel problem. Ill check it out though, thanks for the help!

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[MitchThor14]

No priming needed,

Check  your rubber hoses from the tank sender to the metal lines and the short pieces between the metal lines. 

The rubber can become restricted when they get old.

The bigger line is the fuel feed 3/8. The 5/16 line is the vapor canister and runs to the drivers side.
Pump outlet is hard lined to carb.
Pretty hard to mix them up.

Do the pump test like bd suggested.

Make sure you can draw fuel from the tank to the pump.

Yeah ill probably rip everything apart, before i just blew air through the lines and it went through so i assumed it was clear. Thanks!   

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[MitchThor14]

im sure bd is spot on about the fuel pump but you never did mention if its mechanical or electric

Its mechanical

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[MitchThor14]

Did you put a new fuel pump in or did you buy the truck with a new fuel pump?  Sometimes people forget that the black wire is actually the positive and red is the negetive..

Its a mechanical pump

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