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#1 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Fuel pump, vapor lock? My truck died on the hi-way.
Yesterday after a long three days of new car shopping I was headed home, about an 80 mile trip and my 72 GMC started cutting out and finally died on the side of the road. It's a 72 4X4 with 350/350. It was a hot day, about 106, truck was running cool but suddenly would run out of fuel and die. The fuel filter was empty, no gas. After a while I tried to start it and it fired right up, ran fine. I had a tow truck on the way so I decided to take the tow home just in case it happened again. When we took the truck of the tow truck I could smell gas really bad in the cab, I occasionally got a wiff of gas in the past but this was like someone dumped a cup of gas in there. I let it air out and the truck started right up, there was no gas on the bed of the tow truck or anywhere in the cab that I could find , nothing dripping under the truck, I'm at a loss. Any ideas what and where I should start looking?
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#2 | |
Registered User
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Location: Winnipeg, Mb
Posts: 1,115
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
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#3 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,628
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Do you have a vented gas cap?
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#4 |
Senior Member
![]() Join Date: Apr 2013
Location: Houston,Tx
Posts: 784
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
To me ..it sounds like you may have some sort of vapor lock going on...your truck has (should have) the vent line for the gas tank that runs up the passenger side of the cab..I would start there
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#5 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Thanks, I actually pulled the tank out when I painted my truck, cleaned the pickup tube screen too. The fuel pump is only a couple years old and seems to be working fine. I took the filter out of the carb years ago and replaced it with an inline filter which is clean. Seems odd that I had such a strong smell of gas in the cab but nothing's leaking. I'm really hoping I find the problem, it's running fine now but I don't want to get stuck on the side of the road again. Thanks again.
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#6 |
Senior Member
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Location: Harrison, Arkansas
Posts: 9,815
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Check the fuel line from the pump to the carb. If its touching anything, even slightly it can cause a vapor lock in hot weather, especially with ethanol gas.
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#7 |
Registered User
Join Date: Oct 2013
Location: New Jersey
Posts: 1,305
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
What kind of carb to intake gasket are you using? Had a problem with heat transfer from the intake to the carb and it caused vapor lock. A thick insulating spacer type carb gasket solved the problem.
Paul
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#8 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
It's a quadrajet, thick gasket underneath. The fuel filter was bone dry, no fuel coming through at all. Can a vapor locked carb stop fuel from flowing from the pump to the filter and carb? I have a transparent filter and after awhile could see tiny amounts of gas getting "sucked" through it but wouldn't fill up. I just got back from driving it and it's running fine. The gas smell in the cab is also gone.
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#9 |
The Older Generation
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Location: Montezuma, Iowa
Posts: 25,518
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
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Did you check the rubber fuel line under the cab? It may be cracked or have a hole in it. There is also a vent line in the cab that loops up on the passengers side by the rear window. That may be where the gas smell is coming from. LockDoc
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#10 |
Registered User
Join Date: Feb 2011
Location: Modesto, CA
Posts: 2,188
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Yeah, you shouldn't be able to smell any fuel in the cab. I swapped my 71 tank for the 69 tank to get rid of that vented hose as it's one more thing to deteriorate. That is a good place to start.
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#11 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
They looked in good shape when I put the tank back in but that was five years ago so I imagine they could be bad now. Do you see any reason that would prevent fuel from getting to the carb but not leak any noticeable fuel anywhere, other than the smell? Could the venting system allow air into the gas line but not allow fuel to leak out somehow? I've looked at a schematic of the vent and fuel line routing and can't picture how that could happen but I'm exhausted and might not be thinking straight! Thanks for the suggestion!
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#12 |
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Join Date: Jul 2007
Location: Fall River California
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
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#13 | |
The Older Generation
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Location: Montezuma, Iowa
Posts: 25,518
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Quote:
A hole or crack in the fuel line under the floor could suck air and prevent the fuel from reaching the pump, and a crack in the rubber line on the vent tube could leak fumes into the cab but neither one would affect the other.... LockDoc
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#14 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
I'll check them out in the morning, probably replace them anyway as I'm sure they're the originals. Now I have to drain 20 gallons of gas out of my tank! Hope I have enough gas cans.
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#15 |
member #16
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Location: Yuba City Ca.
Posts: 3,618
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Just unscrew the line from the tank sender and break the suction.
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#16 | |
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Join Date: Jun 2010
Location: San Diego Co.
Posts: 1,167
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Quote:
Can't see that causing fuel starvation though. Fuel pump going intermittent??
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#17 | |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Quote:
Thanks!
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#18 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
I'm going to replace my rubber fuel lines in the cab and under my truck today, I'm seeing a lot of black particles in my filter, I'm assuming it's deteriorated rubber breaking away inside the gas line, I can't think of anything else that would be black in there, anyone know what size line was used on these trucks in 1972? I drove my truck about twenty miles yesterday, ran perfect till I got two miles from home then it died again, luckily it was downhill all the way to my driveway.
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#19 |
Junior Member
Join Date: Mar 2007
Location: Hideaway, TX
Posts: 4,950
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
My guess is fuel pump.
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#20 |
Registered User
Join Date: Dec 2013
Location: Mustang ok
Posts: 24
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
the tank can pressure up due to heat and if your vent is clogged it wont depresurize until the pressure gets high enough then its probably blowing the pressure out of your vent line into your cab then the truck starts because the pressures gone
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#21 |
Registered User
Join Date: Jul 2011
Location: strausstown pa
Posts: 3,394
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
it sure does sound like the rubber fuel hose collapsing under suction.
the ethenol in the gas nowadays destroys the rubber quickly from the inside out. also use a flashlight and check inside your tank for crud or the source of your black particals
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#22 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Well I pulled my tank, dumped it out, found the screen on the pickup tube had deteriorated, the lines were full of little pieces of it. I replaced all the gas line with new, added a big filter inline under the truck where the gas line comes through the floor, changed the filter and line on the carb and the fuel pump. I didn't see any real issues with the gas line other than it being old and starting to crack but it's all new now. After all that I fired the truck up, it ran for about 40 seconds and died. No gas getting to the carb filter. All I can do now is replace the fuel pump, of course my local NAPA didn't have one in stock so I won't know if it's the ultimate problem or not until tomorrow when it arrives! Any ideas what I could have missed? I'm hoping it's the fuel pump and if so I hope the new one last more than 10 months!
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#23 | |
The Older Generation
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Location: Montezuma, Iowa
Posts: 25,518
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Quote:
Did you blow all of the lines out with air pressure while you had it apart? Mine had a lot of solid gunk in the steel lines. I used an old speedometer cable (the inner part) and rodded my lines out then used the air hose and blew them out good. I got a lot of junk out of them.... LockDoc
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#24 | |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Quote:
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#25 | |
The Older Generation
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Location: Montezuma, Iowa
Posts: 25,518
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Re: Fuel pump, vapor lock? My truck died on the hi-way.
Quote:
No problem. Keep us informed on the outcome for future reference. LockDoc
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