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Old 04-01-2012, 09:53 AM   #1
LowOnGas
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Thumbs down 5.7L cutting out while driving

I have a 1984 Chevy k10 SCLB 4x4 with the dual tank setup. It's got a 350, 600cfm edelbrock carb, edelbrock intake, and vortec heads. TH350, stock exhaust manifolds, true duals and flowmaster 40's. 12 inch lift and 39.5x15x15's. I think that about covers it.

Here is my problem, The truck drives fine on a typical trip in town, but under heavy acceleration or high speeds it cuts out. The truck simply is not getting enough gas. When I originaly bought the truck the guy thought something under the hood was messed up because it would always die on him. I played with it some and found out it had a pinched fuel line above the as tank. However, it was not getting enough gas and it seems to be doing the same thing again. The fuel line is not pinched as I have followed it from tank to carb. The fuel pump seems to be working fine as I have an inline pressure tester attached to it. I bypassed the fuel tank select solenoid under the suspicion that gas was being restricted too much when it's going through the valves and such inside this selector.

When I am driving, I can punch it and it will run fine until it pulls the bowls dry. Once the bowls run dry the fuel delivery system doesn't seem to be able to keep up with the carb and the motor starts cutting out. If I back off the accelerator and drive at a reduced speed for a couple miles I can then attempt to speed back up.

I am beginning to wonder if the stock fuel lines and/or stock fuel pump may be unable to keep up with this setup? Many many people put similar upgrades on their rides and I am wondering if anyone else has had this problem, or if someone can offer any advice or suggestions.


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Old 04-01-2012, 10:08 AM   #2
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Default Re: 5.7L cutting out while driving

carb jets set to lean maybeye.

the ome pump and lines should be fine on a 600 cfm
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Old 04-02-2012, 01:08 PM   #3
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Default Re: 5.7L cutting out while driving

Good stuff, I will keep that in mind. I reconnected everything the way that it would be stock (in reference to me bypassing the tank selector solenoid). I also dropped the passengers side fuel tank. It had about half a wheelbarrow full of dirt caked inside the shroud, ontop of he tank and all around it. My wife even found a 16g shotgun shell in the mix. But either way, I am going to repair/replace this fuel tank and switch back and forth to see if I can further isolate this problem. I have been distrusting of all the rubber/metal connections that run through the frame as they make their way to the hood, as I feel even one loose connector could be causing it to pull air through the connection as the demand for fuel increases, causing the cutting out issue.

As a side question, I have looked all through my Haynes maual and I can't quite seem to find an answer. Question is..What are the 3 hoses on my fuel pickup assembly(in tank) for? One I know is fuel as I have tested them, but what are the other two for? They seemed to be inert, which could potentially be part of my problem.
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Old 04-02-2012, 06:03 PM   #4
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Default Re: 5.7L cutting out while driving

should have one that is a vent if im not mistaken. im not sure on all that.

it shouldnt pull air unless there is a hole in the line and if so it would leak gas too. diphram in carb could be bad too the 2bb on my 350 buick has that issue it quits after it runs for about 20 mins.
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Old 04-02-2012, 10:06 PM   #5
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Default Re: 5.7L cutting out while driving

Exactly, I have rolled it back and forth in my head trying to speculate on those two other lines. But it just isn't making sense..the pressure bleedoff I assumed was done through the gas cap, but that would certainly explain it.

And the issue with the gas leaking out of any holes..I thought of that same thing but after some deeper thought into the workings of it, I confused myself. I'll explain it to you and see if my resoning make sense. I figure it like this..When the truck is sitting without running, you have no pressure anywhere in the system. With key on it pressurizes from the fuel pump to the carb to 9lbs positive pressure. As I accelerate the pressure infront of the fuel pump remains 9 or slightly below..However between the tank and the fuel pump, there will be negative pressure (maybe no more than 5 lbs?) because of the vaccuum from the carb/intake manifold. Meaning there really wont be any positive pressure to push gas out, but negative pressure to pull air in..so unfortunately I stand a low likely hood of a leak betraying itself.

I may be WAY off and overthinking this stuff so point me in a direction here, haha. My mechanical experience is limited to putting a pushmower on the curb when it wont start so any advice is helpful!
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Old 04-07-2012, 10:50 PM   #6
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Default Re: 5.7L cutting out while driving

Wow ok, to fill in on some of the recent findings. I had reconnected everything and to my awesome discovery I noticed a fuel line with a hole in it about the same diameter as a spaghetti noodle. I noticed this out on a swimming trip on the Sabine River. Thankfully I had everything still in the truck to make the repair, so I replaced the section of line and had complete confidence in the truck. So much confidence infact that I drove it all the way from Fort Polk Louisiana to Fort Hood Texas(I drove slowly so it took about 10 hours)! And although I was easy on it, I made it without a hitch..until about a mile and a half from home;when it started cutting out again.

I've been tooling away, exploring random options and possibilities and I've come to a decision. I know nothing about carburetors but I can understand pipes and wires. So since the carb is at the front I decided to start at the back and eliminate everything else.

The three lines from the in-tank fuel pickup? One ties into the other tank with a simple "T" fitting and runs to the front of the vehicle. The other two lines run through the fuel tank select unit. The two lines on the fuel tank select are apparently pickup and return lines. Pickup of course runs straight from the select valve to the fuel pump. The return line runs all the way up the frame rail right to the engine bay...then has a bolt and a pipe clamp securing it closed. The other with the "T" fitting runs to what looks like a big vaccuum(charcoal?) canister with numerous other lines that all dead-end or just loop back into themselves right there in the front driver-side engine bay. I disconnected it and blew on it to see if it was stopped up, I experienced no real resistance. I also went to each tank and blew on the same hose at these ends to make sure all three ends of the hose could allow air travel. So the three-line theory got shot in the foot.

I considered the notion that the fuel tank wasn't able to get air into the tank to replace the fuel that was leaving..so I took the gas cap off and drove around, it continued to cut-out.

I changed the fuel pump as it was another possibility, but to no avail...changed it several times and made no progress..it is also mounted in the correct location within the engine bay and keeps pressure (as I had installed an in-line pressure gauge).

Since I still have the tank on the ground and some fuel pumps..I plan on hooking up a fuel pump at the tank end (with a hose coming from it into a gas can). I plan to pressurize the entire system with gasoline in the hopes that any possible leak will show up. If this doesn't give me any results I intend on bypassing the ENTIRE series of pipes and hoses so that I have a single fuel line running from the tank straight to the fuel pump then to the carb so as to eliminate the possibility of any obstructions existing in the lines.

If anyone knows anything or can give me any advice on this I'm open to any possibilites. Ideas, theories, speculation, I'm running out of steam on this project. I feel that fuel isn't reaching this carb like it should. When it cuts out and dies, a couple times I have disconnected the fuel line at the carb and I find a large section of air in the line. When there is fuel in the line the pump keeps pressure on the carb even after the pump is off. This truck is older than I am and it certainly seems wiser because I've learned alot so far and this ain't over yet..but it ain't gunna win this fight.
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Old 04-15-2012, 02:00 PM   #7
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Default Re: 5.7L cutting out while driving

For anyone that was following this post the final conclusion is that the carb was soaking up a bunch of heat off the engine and cooking all the fuel out. My fuel pump was an electric pump mounted under the hood as well it was soaking up a crap ton of heat. I moved the fuel pump to the frame rail (right between the fuel tank select soldenoid and the frame rail). I intend on ordering an insulating carburetor gasket/spacer. Seems like an awesome idea. As well, I realized I had some mild issues with the truck trying to overheat;I found a 165 degree thermostat in it. The truck calls for a 195, the manager at advance told me the 195 would make the truck overheat way worse and wanted to argue with me about my reasoning behind heat exchange. That motor ran about 175 with that 165 degree thermostat but when I ran it hard the temp shot through the roof until it cooked the carb and fuel line. I figure if idling it runs at 175 thats almost the same as having no thermostat if the thermostat stays all the way open all the time anyway. I dropped the 195 in it and it loves it, the cooling system can keep up and I dont have water dripping out of my exhaust. If anyone else has any advice for me please dont hesistate, I've learned pretty much everything off of the internet and telephone so I've got alot to learn still.

Last edited by LowOnGas; 04-15-2012 at 02:06 PM.
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