Broken hearted kid and fuel system

[Mossyman]

A truck that runs on no fuel? Sign me up…

 

[Vetal4]

Any possibility there is a venting issue?

This. You seem to have eliminated the fuel line as a problem, could still be an air leak, but it starting up when you took the hose off…that sounds like the pump can only slowly pull fuel and when you disconnected the line the pump was able to pull what fuel that was in the line to the float bowl….if I’m reading all this right.

 

[RaisedK5]

Only other thing I can think of that hasn't been mentioned is if the return and supply hoses got switched accidentally it couldn't pull from the tank. Might want to retrace the routing.

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[Travlr]

@medic503 stay with it. Y’all are so close! I say electric fuel pump lol suggested above. Cheap and easy fix.

On a side note.. don’t quit! Easton bought his square with his money at 14.. we worked on it for 2 years to get it where it is today and I can’t tell you the number of times I wanted to quit and sell that thing. The folks here saved me more times than I can count and in the process, made me look a lot smarter to my kid than I actually am! Now at 17, he has his badass daily driver! It still has things here and there to work on.. but the life skills he learned by doing it (with everyone here!) you can’t put a price tag on any of it. It was (still is) something we as a father and son will never forget!

I’m following this thread .. please keep us posted.

Randy and Easton

Best thing I ever did with my son was to build a '70 Chevy p-up. We both learned a lot from that experience. Including the frustrations...

 

[75gmck25]

First - I want to make sure this is how it’s plumbed
- you have the fuel inlet hose from the tank connected to the 3/8” Barb/push-on fitting and it has a clamp. It should be a short hose that runs over to a 3/8” line on the frame rail, with a clamp on that end.
- small barbed fitting should also have a short hose running over to a metal line on the frame rail. This is the fuel return line.
- square fitting is threaded, and there should a metal line connected. This line runs up to the carburetor inlet. The line may have been cut near the carburetor to add an external fuel filter.
I’ll post a picture of my fuel pump as soon I have one. Added the picture of the 3 port fuel pump .

Now crawl under the truck by the electric fuel solenoid and find the other end of the metal fuel supply line, and disconnect it from the solenoid. If you only have one tank you don’t need the solenoid and it just complicated the troubleshooting.
- first possible test - use a barbed fitting and/or 3/8” hose to extend this line to the fuel pump and drop it into your gas can. If it properly supplies fuel and the engine runs off the gas can, you are one step closer.
Go back to the solenoid and disconnect the other 3/8” line, which should run back to the tank sending unit.
- now connect this sending unit line from the tank directly to the metal line fo the pump, and check to see if it runs.

If it now works, then do the same (bypass the solenoid) with the return line to the tank.

There should also be a metal tank vent line that you haven’t mentioned. There will be one hose from each tank, then a T fitting, and then a connection to the metal vent line that runs up to the canister under the hood.
Don’t be surprised if some confused owner who thought it was just “emissions crap” disconnected the vent line and/or removed the vapor canister. You definitely need venting for the tanks, either a proper vent to the canister, or vented gas caps.

 

[Grit dog]

^Thats a good possibility too.
At this point you’ve verified everything from the inlet to the fuel pump through the carb is fine.
On to the lines, tank selector and fuel pickups.
And agree, although you’ve done some work there, it is likely easiest to pull the bed and just give yourself good access to everything all at once.
If the bed bolts are frozen up don’t waste your time trying to free them up. You can get to every nut on the bottom with a **** wheel. Cut them off. New bed bolt kits are $15.
1 ground strap
Rear diff vent
Tail lights and grounds
Wire loom attachment at the license plate lights
Fuel filler hoses
That’s all that needs to come apart to pull the bed.
And a couple buddies and a couple saw horses if you don’t have a cherry picker or chain hoist etc.

And it’s the perfect opportunity to do whatever else it is you may want to do to the back half of the truck.

 

[Craig Nedrow]

James, lots of good advice here, but lots of jumping around. Start at the source, the tank first. Disconnect the fuel line at the selector valve under the truck, gas should run out, lots of gas. If not, there is the problem, it's plugged. Just try that first and see what happens. If lots of gas runs out, good, that tells you it is not the tank or the components inside. Bypass the under bed selector valve previously mentioned, go straight to the fuel pump. Disconnect the line that goes to the carb in the engine compartment. Use a can to catch potential gas, and crank the engine over, you should get lots of gas, shooting out every time the pump pumps, it should shoot out. This will tell you everything you need to know. I believe from what you have said, it is most likely a fuel delivery problem. Once you do this, it will tell you where the problem lies, plugged tank, bad fuel delivery which is the pump, cam lobe, or cam fuel pump pushrod. Cam lobe/push rod can be checked, but try the above first. It is NOT, spark, carb, carb filter or air, as it runs.

 

[andybflo]

I'd tend to agree with the folks above; you are either routed to a vent/return on the selector instead of the fuel pickup (my '86 uses the same size for return and suction.) Or you have a pinhole.

No need to replace the Carb, it's working enough to get the motor to run. No need to replace the pump. It'll suck fuel.

My advice? Pull the rubber jumper off the selector valve, on the tank side. Apply vacuum. See if you get fuel. Even from a cheap electric pump, your lungs (don't inhale fuel, please), a hand vacuum pump, etc.

You get gas, that section of line is correct.

Next, fuel pump to the other side of the selector valve. Pull it off the valve and plug it. See if you can draw/hold vacuum. Slightest pinhole, any pump will happily suck air over liquid. Pumps like to push, not suck.

I'm betting there's a dryrotted rubber jumper somewhere, or a pinhole. If you live like me, in the north, those lines were rotten sometime in the mid-90s, at the latest... Pol lock (It's one word, but it's censored here.) still makes the valves. If you get/can maintain suction on both sides, I'd look at the valve itself. There are tiny pieces of rubber inside the valve that create a seal. If one tore or dryrotted when it sat it won't allow you to build vacuum and suck the fuel forward. Heck, bypass the valve with a few feet of rubber hose temporarily from your full fuel tank; I wouldn't run it down the road like that forever, but in your garage/around the block, it'll be fine if it's kept away from heat and spinny things under the truck.

Just my opinion, and my 2c. You've spent enough time eliminating stuff on the top-side of the truck. I'm betting it's underneath.

As a guy with Q-Jets and 4150s... On a street truck, the Rochester is a better carb. They're just more complex, so people toss them before they learn how they work. They blame the carb as the problem, instead of their lack of knowledge. GM shipped millions of Q-Jets; from Corvettes to pickups, they worked well, and can be tuned easily. And mechanical pumps worked forever in production vehicles; solve the problem, it'll work fine here, too. Only think an electric pump will give you is an easy way to find the leak... (look for the wet spot.)

 

[flyboys]

Ok yall, Ive got a situation and I cannot figure it out. I am not a mechanic by no means but hoping someone here can point me in the right direction. My son was gifted a 1984 Chevy K10 with a 350 motor by his grandfather. For those that work at a parts store, yes its four wheel drive. It has the regular quadrajet carburetor on it. The problem is, we cannot get gas into the carburetor and I cannot figure out why. We have been working on this thing for months and each time we discover something new, he gets excited because we finally think we have found the problem. We fix the issue, and it still doesnt work. Last night we worked for three hours just to try to start it til the battery died. He just hung his head and started crying and its killing me. I love working with him on it to help him restore it but im also tired of throwing time and money at something and getting nowhere. Fuel is not getting into the carburetor and i cannot figure out why. His grandfather said it ran before, it just needed the carburetor cleaned because it had been sitting for about 7 years and the fuel tank selector switch needed replacing. Here is a list of everything we have done.

- When he first got the truck, the carburetor was taken off and given to a mechanic to clean. He cleaned it and did a few other things to it and we got it back. Wouldn't work.
- bought and installed a new fuel tank selector switch, didnt work.
- dropped the passengers side tank and cleaned it out, put in a new fuel sending unit. didnt work
- Bought a new mechanical fuel pump for it and put it on, it ran for 4 minutes and then didnt work. There was fuel in the pump when we removed it.
- Bought new spark plugs and wires, didnt work.
- Found out my son didnt get all of the water out of the gas tank before the tank was put back on so we dropped it again cleaned it again and got ALL water out. It was dry as a bone. Replaced everything and filled with gas, ran for 2 minutes, wouldnt start.
- Bought a new mechanical fuel pump just in case water messed up the first one, still didnt work. There was a little fuel in the pump when I removed it.
- Ran a line from the carb to a bottle of fuel, works fine.
- Blew air through all the lines and there was no fuel anywhere. I couldn't hear any leaks, but there was no fuel when I moved my finger off the hose and I felt the air.
- just in case, all rubber fuel lines were replaced. still didnt work.
- Tried the bottle thing again, ran fine. However, no fuel in the lines that I could see.
- Replaced the tank selector valve, no gas anywhere, still wouldnt start
- Checked the rotor cap and its clean and replaced just as it was. Ran fine off a bottle.
- Found out about a push rod that makes the fuel pump work (had never heard of this before) but went and bought a new one. When we pulled the fuel pump off, I there was one already in there and I could tell that at the bottom of the arm on the back where the rod had been hitting it at the tip. So Im assuming that is working properly.
- Last night we replaced the metal fuel line with a rubber one on the front of the motor. That is literally the only part of the fuel system left that had no been replaced (except for the metal lines) on the passengers side. Still wont start.

Just for ***** and giggles last night, I read about priming the carb. We poured a total of an entire 20 ounce bottle of gas down the carb choke side and it would run until the gas was burned and then cut off. We tried starting it until the battery died and when it died, so did our ambition.

So, what else could it be that is causing the fuel not to get into the carburetor. I did pull the fuel filter last night and it was pretty clean, there were some black dust looking things on it but otherwise it was clean. It had fuel on it but not as much as I imagined it should be. The check valve was installed on the nut side of the carb. Is that backwards? What am I missing? Just an FYI, all of the work was done on the passengers side. We have not touched the drivers side. We wanted to get one tank working and then focus on the other one. Could that be the problem? I am so tired of throwing time and money into this thing and not getting any results. I only have 3 months until he gets his license and I dont have a lot of time to work on it. Someone please help!!!!

Hope I don’t make myself out to be a complete idiot here… but would strongly recommend you go back to the fuel tank and check you connections. I had to replace one of my tanks due to a leak. Bought everything new. Dropped the tank from underneath- took pictures to make sure I put new stuff back together correctly. Added about five gallons of gas and hit the switch. Ran perfectly! So I go up to gas station and top her off (another 11 gallons or so). Switch back to old tank and drive down the road to the interstate- switched to new tank and went about 1/2 mile and truck shut off! Back to old tank and head home. Dropped the new tank (full of gas now ) and figured out my new hoses were to long and was getting pinched closed when the tank was mounted. So all that to say - check the hose lengths and make sure you are not having the same issue I did. I couldn’t see the pinched hose because I was working from underneath-

 

[Oldguy]

I struggled with the same issue. The fix for mine, (not saying it’s the problem with yours) was that the short section of rubber fuel line from the sending unit to the metal fuel line was kinked after I replaced the tank. I fixed that and it ran like a top.

 

[seniorbear69]

hi had same troble with an 84 c20 i purchsed. went through whot you going through
so i started at the carb with bottle all good .tghen same bottle other side of pump. all good end of metall fuel pipe wear selector valve was joind bottle all good.so completly removed valve put fule in tank all good .replaced valve .would not start .turnd out to be the switch its self was constantly on lh tank which had not been looked at .remove the valve conect directly to chassis lines it should run .then you can mess with the rest whilst the lad can drive it .good luck .steve

 

[bookit]

All right team lets quit over thinking this problem!!
Won't run in factory configuration of fuel system!!
Runs like a baby when it is bottle fed.
You have changed the fuel pump how many times??
Did you bother to check to see if the fuel pump push rod was moving, perhaps the push rod is seized or stuck in the block bore or possibly the camshaft eccentric is worn excessively.
I had a 86 K5 Blazer that would not allow any oil to flow past the push rod and the pump would fail a few months later, I finally ground a small spiral groove into the push rad and it the pump never failed again.
The easy answer is to bypass the original pump with an electric pump and drive it like you stole it.

 

[CountKrunk]

Hey man, you make any more progress?

 

[SquareRoot]

Hey man, you make any more progress?

^^^^^^^Define progress. lol

 

[squaredeal91]

I've been curious myself. I know this truck is going to run soon! I wonder if it's flooding when he hooks it up to fuel and runs when it's unhooked on what's it. I've actually had that scenario before.