Fuel issue while driving

[76chevyc20454]

Ok starting from the beginning I bought this truck back in February and the guy I bought it off of said he had a problem with it vapor locking. Ive only heard of this gaping after you turn the motor off but anyway he added a electric fuel pump behind the mechanical. Yes the mechanical is still hooked up so it almost acts like a primer for the mechanical. It is hooked up on a toggle switch. He told me that if it vapor locked to flip the switch for a couple of seconds and turn it off and it should be fine. He also mention that it only happend when he pulled heavy loads. Well if I drive it more than a half hour it will go from cruzing tpm and cut out so I'll turn on the switch for a couple of seconds and it will run fine for a lil then do it again but if I leave it on while driving I have no issues with it doing that. Just confused on why he didn't put a regulator on it and get rid of mechanical. What you guys think could be going on .

 

[76chevyc20454]

@HotRodPC

 

[chengny]

I think you have an air leak in the rubber section of the gas line:

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But that's just my opinion and - without more details - is a WAG.

 

[HotRodPC]

Either what Chengny is saying or your manual fuel pump is taking a dump.

 

[76chevyc20454]

Ok i will check that and that's what i thought about the mechanical. i wanted to bypass the electrical fuel pump and see how the mechanical does but don't wanna get stranded.

 

[HotRodPC]

I had an electric pump on my 64 GMC too, for the exact same reason you did. It saved my ass once when I was 6 hours out of town. I'd leave the electric pump if I were you. They are flow through when off, so the manual pump can pull through it. The electric fuel pump can even help if you get a clogged fuel filter. It'll add pressure and be able to push the gas through all the **** in the filter. And then of course if you vapor lock, then you have it too.

I've also used the electric pump to save a buddies ass and we were out of town. We had taken his boat out skiing about 1.5 hours from home with the girls and kids. His square didn't have a fuel gauge. It was windy that day along with pulling the boat, he used more fuel than normal and ran out on the freeway. Since I was following him with my Gf and daughter, we pulled over behind him. He had an empty boat fuel can. Disconnected my fuel line at the carb, put it in the gas can, turned on the electric pump and pumped him 2 gallons out of my tank to get him to the next offramp and some fuel.

Just some reasons, I'd leave the electric pump since it's already there.

 

[Rusty Nail]

An update on the gas cap status is needed.

 

[76chevyc20454]

An update on the gas cap status is needed.

I just put a new locking one on about a week ago, problem is still there.

 

[76chevyc20454]

I had an electric pump on my 64 GMC too, for the exact same reason you did. It saved my ass once when I was 6 hours out of town. I'd leave the electric pump if I were you. They are flow through when off, so the manual pump can pull through it. The electric fuel pump can even help if you get a clogged fuel filter. It'll add pressure and be able to push the gas through all the **** in the filter. And then of course if you vapor lock, then you have it too.

I've also used the electric pump to save a buddies ass and we were out of town. We had taken his boat out skiing about 1.5 hours from home with the girls and kids. His square didn't have a fuel gauge. It was windy that day along with pulling the boat, he used more fuel than normal and ran out on the freeway. Since I was following him with my Gf and daughter, we pulled over behind him. He had an empty boat fuel can. Disconnected my fuel line at the carb, put it in the gas can, turned on the electric pump and pumped him 2 gallons out of my tank to get him to the next offramp and some fuel.

Just some reasons, I'd leave the electric pump since it's already there.

Yea, is it ok to leave it on? i have no clue what psi it runs, the only thing i no is that its a Mr. gasket pump. i got told that if its higher than 4-6 psi that the mechanical would stop it from pushing more than 4-6 psi. im sorry if i confuse you lol.

 

[Rusty Nail]

Does problem exist while running without a gas cap?

 

[Irishman999]

I had just about every fueling issue you could imagine with my 85, everything seemed like vapor lock to me. There is countless pages on here from years ago about my truck running like **** after driving around for a while, it even had trouble restarting after shut off hot. I tried 2 new fuel pumps, new carbs and even an aluminum intake with a phenolic spacer to keep the carb cool.

That turned out to be the PCV valve not being hooked up for years, I did not know it needed to be hooked up at all. My dad and I plugged one in and it ran like a top.

Another completely different problem that felt like vaporlock- If I drove my 85 on the highway it would just **** out like I ran out of gas. I would usually panic and take the next exit and suddenly everything is fine after I slowed down. It completely felt like a thermal issue.

What it actually turned out to be was a completely clogged up carburetor. I had a clear filter mounted right before the the carb inlet because I was changing it so often. The filter looked fine and was flowing fuel but when I removed the top of the carb everything was packed full of what looked like black sand.

It was decomposed rubber hose and it can get past fuel filters apparantly, I cleaned out the carb and replaced some lines on the selector valve under the truck and its been fine since.

 

[76chevyc20454]

I had just about every fueling issue you could imagine with my 85, everything seemed like vapor lock to me. There is countless pages on here from years ago about my truck running like **** after driving around for a while, it even had trouble restarting after shut off hot. I tried 2 new fuel pumps, new carbs and even an aluminum intake with a phenolic spacer to keep the carb cool.

That turned out to be the PCV valve not being hooked up for years, I did not know it needed to be hooked up at all. My dad and I plugged one in and it ran like a top.

Another completely different problem that felt like vaporlock- If I drove my 85 on the highway it would just **** out like I ran out of gas. I would usually panic and take the next exit and suddenly everything is fine after I slowed down. It completely felt like a thermal issue.

What it actually turned out to be was a completely clogged up carburetor. I had a clear filter mounted right before the the carb inlet because I was changing it so often. The filter looked fine and was flowing fuel but when I removed the top of the carb everything was packed full of what looked like black sand.

It was decomposed rubber hose and it can get past fuel filters apparantly, I cleaned out the carb and replaced some lines on the selector valve under the truck and its been fine since.

My PCV valve is hooked up and i just cleaned the carb on it and that didn't help. The carb didn't look to bad when i pulled it apart. It almost did the same thing you describe.

 

[Irishman999]

My PCV valve is hooked up and i just cleaned the carb on it and that didn't help. The carb didn't look to bad when i pulled it apart. It almost did the same thing you describe.

You can solve it the wrong way like I always do and just start replacing everything it could be until you stumble on one single problem that fixes it for almost no money or just rule out problems.

Hotrod makes good points with the electric fuel pump but I would eliminate it right from the get go only because the truck did not need one originally and it does not sound like you need to pump a ton of fuel. Its just adding another variable to the list of things that could be wrong, fuel could pass through it no problem who knows for sure?

Next I would replace all rubber fuel lines you find in the system all the way from the tank to the Carb. You will find a nice little cluster at the fuel tank selector valve.

Once thats out of the way I would just order a new mechanical fuel pump from summit, they have a cheap unit that flows fuel like crazy. You can also check your pump without a gauge using a small container to catch fuel and someone to crank the engine. You will have to google that one because I cant remember how its done exactly.

The original setup to a q-jet is a metal hard line going behind the water pump up to the carb but like every other square on the planet someone probly chopped the hard line and ran some rubber hose. Thats fine, it works no problem. To be double sure your fuel is not getting hot in the engine compartment put some thermo sleve around the fuel line all the way to the carb and zip tie it out of the way of anything giving off heat.

If none of that works I would suspect other problems.

 

[HotRodPC]

Yea, is it ok to leave it on? i have no clue what psi it runs, the only thing i no is that its a Mr. gasket pump. i got told that if its higher than 4-6 psi that the mechanical would stop it from pushing more than 4-6 psi. im sorry if i confuse you lol.

If it's a low pressure pump like for carbed motors you can leave it on. Even if it's up to 8psi you're OK. Just want to make sure it's not a fuel injection strength pump. You'll know pretty quick if it's to much pressure. With to much pressure, the pressure will overcome the needle and seat in the carb and push fuel through anyway then flood the motor big time. In most cases, a low pressure fuel pump doesn't have to be regulated. It's nice to, but not required. You could always google the specs on your E pump and find out what it's supposed to be putting out.

 

[76chevyc20454]

If it's a low pressure pump like for carbed motors you can leave it on. Even if it's up to 8psi you're OK. Just want to make sure it's not a fuel injection strength pump. You'll know pretty quick if it's to much pressure. With to much pressure, the pressure will overcome the needle and seat in the carb and push fuel through anyway then flood the motor big time. In most cases, a low pressure fuel pump doesn't have to be regulated. It's nice to, but not required. You could always google the specs on your E pump and find out what it's supposed to be putting out.

i looked at mrgasket.com and the same pump i have is rated for 4-7 psi so i should be fine. i would think anyway. i heard around 4-6 but with the mechanical in the way i dont think it would push 7. Are some pumps adjustable, just curious? another thing he mounted the pump on the inside of frame really close to exhaust with some star foam tubing around it, i guess to keep heat off of it. should i try moving it to outside of frame away from exhaust or leave it alone?