Mechanical fuel pump

BJedi76

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4x4 86’ GMC sierra classic 1500 w/305”

Had a fuel leak down near the pump. I decided to just have the fuel pump and the steel line going to the carburetor replaced.

I pick the truck up from the shop, drove 7 miles to the gas station, and then 8 miles home.

15 minutes later I went out to the truck, with the intent to dial the carburetor in a bit better. I started the truck and 15 seconds later I heard a pop and the truck stopped running.

Spraying starter fluid in the carburetor, the truck ran fine until I stop spraying. I removed the steel fuel line from the carburetor and crank the truck over. No fuel...

I had the truck towed back to the shop and I walked home. Within an hour, the shop called me back saying the truck just started when they turn the key, and they were able to simply drive the truck into the shop.

I am currently waiting to hear back.

does anybody have any educated suggestions, on how this is even possible..?!?
 

Swearbody

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Possibly vapor lock. The truck sat and the intake/carb was hot and without pressure or cooling so fuel vaporized. Would be my first thought. The pop may have been a lean backfire.
 

Swearbody

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Then it sat there and cooled/condensed during the tow and fired up fine
 

fast68chevy

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still got the EST/ESC E4ME carb and disributor on it? could be malfunction of knock sensor ignition timing retard function of the ignition module even.. as well.. and the carb could be stuck in VERY lean fuel mixture mode. theres going to be a ton of things to check and that it coulkd be. and no way to help without being there to diagnose it.. if it still has the ESC system intact on it and it was mine i would have swapped non ESC carb and distrib on it long ago. the fuel mix solenoid and TPS in these E4ME carbs eventally fail and quit working and cause issues problems of all kinds.. well over 40 years old, it is a miracle that it even runs at all... look at the spark plug tips are they gray or white or black or? thi wil tell you exactly whats been going on how its been running and what it needs etc.
 

Rusty Nail

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Uh huh.

If it were me I would take the gas cap off and try to duplicate the symptoms BUT ! it begs a question about what brought about your desire to "dial in the carburetor better"?

You have stated this was AFTER the fuel pump AND feed line replacement but how was it running before hand?

What kind of gas do you buy? Ethanol or real gas? Is this truck new to you or have you had it for a while?

Y u no haz pix? :mad:

When was the last time you changed the oil?
What brand/weight do you use?

How much air pressure do you run in the tires?

Let's go back to the gas leak...where was it coming from? - does it still leak? What brand of fuel pump did you buy? Does it have a return line?

:pedobear:

Change the filter in the carburetor..
 
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BJedi76

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This truck is a project. I’ve been slowly rebuilding it. Freshly rebuilt Carburetor is a 4M4C 17066559 thermostatic choke w/electric choke conversion.

rebuild kit from Cliff’s High Performance.

Midas replaced the fuel pump. Pump was purchased from O’Reillys.

They plugged the 3rd line from fuel pump. Said it wasn’t necessary.

I questioned that, but they assured me that it was not necessary.

Wouldn’t that mean that the vapor recovery line to the gas tank is vented straight to atmosphere? That seems, wrong to me.

Truck started and ran fine. Idled just over 800 RPMs (no high idle for some reason Revs great. Even drove it around the block. After about 20-30 minutes of idling, it just dies, lack of fuel & Will not start again. If I spray starter fluid of pour gas down the throat, it starts right up and runs until I stop.
 

BJedi76

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BJedi76

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bedwards

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The line is a return to keep the pressure regulated at the carb and send the extra to the tank. I would hook it back up.
 

BJedi76

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Now it won’t run at all unless I pour gas down the carburetor.

I took off the fuel line at the carburetor, and almost no fuel came out.

i’ve taken many fuel lines off of many carburetors and whenever I did, tons of fuel poured out. Always needed a rag under it to catch it. This time just a dribble.

All I can think, is that I have a partial &/or intermittent blockage between the fuel tank and the fuel pump.
 

82sbshortbed

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Id change the paper filter in the carb where the fuel line connects to carb in front. Where it says filter.
 

82sbshortbed

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Plus I'd swap that fuel pump for one that just has input and output rather than pluging the return line if your truck doesn't have that line.
 

bedwards

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Mine doesn't have but a dribble in it when I change the filter and it runs just fine. I have had to drop both my tanks and rinse them out. The little filter in the carb will stop up real quick if you don't have clean fuel. I had to cut the filters I have changed open to see what was stopping them up. It would go from running just fine to coasting dead in no time. All is well after dropping the tanks. There was a powdery substance in the driver side tank that would drop out of suspension if left to sit, but would mix first time you moved the truck and go right to the filter and stop it up.
 

Nonstop

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Two things come to mind -

Check your gas cap - it may not be venting, causing a vacuum

I believe the extra port from the pump was supposed to help prevent vapor lock. Check to see if your truck originally had a return to the tank. If it did, I would hook it back up.
 

75gmck25

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The return line lets fuel return to the tank when the float closes and the carburetor dead-heads the fuel flow , and it helps keep the fuel cooler. Without a return you get hot fuel trapped in the line and it increases the chance of vapor lock.

If your truck has a 3 port sender, then you should use all 3 ports connections at the fuel pump. The metal return line connection should be strapped to the frame very close to the 3/8" fuel line input to the pump.

Bruce
 

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