# Help- 1979 Chevy 4x4 Need Fuel System Help



## Luke79ChevTruc (Aug 18, 2003)

I need help. I purchased a 1979 Chevy 4x4 Truck (454ci) with dual fuel tanks. One tank is brand new the passenger side appears original. This truck had an electric fuel pump that the previous owner said was causing vapor lock and engine shut off. I replaced electric fuel pump with original manual fuel pump and steel line from carb to fuel pump. This truck will only run for about ten minutes and then shuts off. The truck will start up again after cooling down but will only run for about ten minutes.

Can anybody tell me what is wrong and where I can start to troubleshoot the tanks and lines. I know there is a fuel or vapor lock occurring somewhere but do not know where to start. Is there anyway I can make this truck run on 1 tank? Please send any info or advise who I could speak to on this. Thanks Luke.


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## wyldman (Jan 18, 2001)

Welcome to Plowsite.:waving: 

Are you sure it is a fuel problem,and not ignition or electrical ?

When it dies,if you look down the primary side ofthe carb,can you see the accelerator pump squirt fuel when you open the throttle ? Do you have spark ?

If you have spark,and no fuel,then maybe it is a vapour lock,or a tank venting problem.Try it with the fuel cap off the tanks,and make sure you have sufficient fuel in both tanks.

You could also run it off a small jerry can plumbed directly to the fuel pump inlet.If it runs fine,then you have a fuel tank or switching problem.

Try that stuff first to narrow it down,then report back and I'll help you through the rest of the diagnosis and repair.


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## 79Chevy (Jun 21, 2003)

*Hey Luke79ChevTruc*

I also have a 79 Chevy pickup Longbed... I only have a 350 in mine but I did just install the passanger side fuel tank... I had to change out the switching mechanism.. and hoses.. I also have an electric fuel pump.... 
If you wanna ask any questions "Wyldman" is an good person to ask...
but I might be able to help too....
not trying to step on any toes or anything... its just that this site has helped me out a lot and I just want to put back in....

Anyway, look forward to hearing your posts....

Thanks


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## CT18fireman (Nov 30, 2000)

I have heard quite a few problems regarding dual tanks. Most of them in the older trucks. I would think that only changing one tank could be a problem. Did you blow out all the lines between the two tanks and the carb? What about all the vents and breather lines for the tanks?


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## Pusher Joe (Nov 30, 2005)

*fuel problem*

when you installed the pump did you install it properly. there is an ajustment after installation.


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## Detroitdan (Aug 15, 2005)

My 81 had dual tanks, when my switch eventually failed I was stranded on a freezing Christmas eve. Had a full tank on the other side but the switch wouldn't let me get to it. After trying to think of a way to transfer fuel from one tank to the working one, I had a bright idea. I took both fuel lines off the switch and swapped them. From that day on I had to remember that my switch was labeled backwards. Maybe the tank you are working off of is not the tank you think it is, and/or maybe it has something in it that the pump is pulling into the pickup. It seems more likely to me that it is vapor lock. Have you tried checking the whole line to make sure it doesn't come close enough to the exhaust or motor to be getting hot? I saw that before, somebody had run the fuel line up the front of the motor and it was touching the underside of the upper radiator hose, as soon as the thermostat opened it would heat up that one little section of line and vapor lock it.


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## derekbroerse (Mar 6, 2004)

Yeeouch! I hope this guy got that problem cleared up 2 1/2 years ago....


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## Jpocket (Nov 7, 2005)

Why old threads come back like that?


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## rgg687 (Apr 29, 2014)

*trying to figure out my fuel tank solinoid*

any help it is a one wire configuration on the fuel solinoid I have a 1979 chevy 4x4 with a 400 engine 400 transmission I can only get gas out of one tank no vapor lock issues


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## dieselss (Jan 3, 2008)

I'm sure its in the scrap yard by now. how old is the thread?


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## derekbroerse (Mar 6, 2004)

I'm sure rgg687 did a search and this came up. He needs help obv.

Is your solenoid valve switching? You should hear a definite 'thunk' from it when someone moves the switch. Also, moving the switch should also swap your fuel gauge over to the other tank--is that happening? Switches are known to go bad and are only around $20 new. The solenoid valve is a whole lot more money, though I found a generic but functional replacement for a '75 K25 I worked on years and years ago from the local tractor-trailer parts supplier for much cheaper.

Make sure the valve is clean and rust free where it touches the frame (make sure the frame is too). The one-wire setup requires the frame of the truck as its ground in order to operate.

FWIW, my '78 K30's valve was messed up, yet it made the thunk sound switching... BUT it would take fuel from both tanks at the same time!


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