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I have a 1986 Chevy Suburban 2500 5.7L. It runs great when it does. I had to hook up all of the emissions crap in order to register it. It ran great. Replaced the ignition coil, rubber part of fuel lines, fuel sending unit, fuel filter in the carb, and fuel pump, thinking that was the problem. When I drive it for about 20-30 minutes and turn it off everything is fine. Come back after a few and it won't pull any fuel in. The lines are not vaporizing the fuel, from what I can see. It runs great for that little bit. I can get it started with starting fuel, or just by dumping fuel into the carb, then after letting sit, it'll start. Can someone tell me what am I missing?

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Could be lots of things....

1 fuel pump, even though its new. Seen them defective out of the box.

2 fuel line, rusted line will prevent a good pump from sucking the vacuum  needed to get fuel to the pump.

I had a 70 Impala that the fuel would drain back out of the lines into the tank. Took it about 45 seconds to start every time it had sat overnight. My grandmother bought it new, I got it from her. It was like that from day 1.

Install a electric pump and see if that solves the problem.

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An electric pump is my next step. Unfortunately, it started after I owned it for a year. Then the old engine blew, and I swapped engines, and now that's all it does. I also need to rebuild the carb. Thanks for the info!

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So you can pull the line at the carb. and no fuel spits out when cranking? But once it's running, it runs and drives fine?

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So, it will start when it's cool. Even holds fuel in the line so it can start. (After a couple of days it'll drain.) I've only pulled the line after it gets warm and won't restart, or until it quits on me, and yes, no fuel spits out when cranking. When it dies, it starts chugging like it's out of fuel and then won't restart until it's cooled off. Yet the fuel lines are warm, yet touchable.

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Did you hook charcoal canister wrong?try leaving gas cap a little loose for a test

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Did that. It still died while idling with the fuel cap off, after I got it back home and waited about 20 minutes. 

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Darn,what if you took fuel feed off of pump,and lowered it,to a container,it should siphon on it's own,stuff in tank sloshing around? clogging sock?

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Tank is clean. No debris. The fuel sending unit was just replaced, then tried it again. Hasn't changed.

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I'd still wonder if you're sucking air somewhere in the system. Either at the sending unit fittings or along the fuel line. Have you checked that the fuel pump is developing the required vacuum to  bring the fuel to the engine? This burb only has one fuel tank correct? If you hadn't mentioned already replacing the fuel pump, I'd go there, but..... of course you can get a bad pump out of the box. That's why I'd suggest checking it's suction ability. As mentioned above, if you pull the tank line from the pump it should continue to drain/siphon, at least it always does when replacing them on my '79 & '80

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Yes, one tank. Okay. I'll try it. I haven't checked the pump because it was the second one. I have found a line that goes somewhere by the canister area, not sure where it gets hooked up. It looks like it might be the return line for fuel? I'm going to try following it back, if I can.

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At the pump you've got:

Fuel from tank

Fuel to carb

Fuel return to the tank

 

I re-read your first post... once you get it going it runs fine... so it would seem to be supplying fuel at that point.

I'm still wondering why seem to be lacking fuel according to your description, if that's what is happening

 

After shutting it off,  It should start and run again until the float bowl is dry, even if the pump didn't supply another drop.

 

You've got rule out fuel pump supply if that is the issue at all. When no start, try removing carb line at pump, put a hose on it run to a jar, while someone cranks it. If it's supplying a strong flow of fuel than you can move onto something else. Either carb itself or ignition

Edited by txab
sp

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Sounds like a case of vaper lock.

Hear me out.

Only time it won't start is when hot. No fuel in the line when hot.

 

When cold you have fuel in the line and it starts. So the fuel must be vaporizing when hot.

 

Stays running once started hot/cold because you have cool fuel being pumped into system.

 

We're do you have the fuel lines ran?

Edited by Mikebtte

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Yes, after restarting, it will run and burn the fuel in the bowl. Then no start until I force it with filling the bowl with fuel and pumping fuel through the lines. I thought it was vapor locking, but the lines are run along the frame, the original way I believe, and they're cool to touch when it does this. 

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What do you mean,pumping fuel thru the lines?how are you doing that?I'm wondering,if you had a can of fuel ready when it fails on you,pull off pump feed,block feed with a bolt,have suitable length of hose ready,hook it up to pump and pull out of can? 

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