Blazer gas tank plugged vent tube at the tank.
 

We completely rebuilt a '72 Jimmy for my son. Original tank. It was flushed out and looks good inside. Now that the truck is on the road we have found the vent tube going into the tank is plugged. I can put 100psi of air pressure on it and it just blows back out the vent opening. If you hold the rubber nozzle on it tight enough after you stop adding air and let off, it vents pressure back out. So NOTHING goes into the tank.

Anybody had one of these tanks cut apart? Is there some sort of one way valve inside the tank? Trying to push a coat hanger through it forcibly contacts something, and that does not happen in the smaller charcoal cannister fittings. I have an air vacuum pump I may try to hook and and see if it might pop a valve loose.

Re: Blazer gas tank plugged vent tube at the tank.
 

There is only a valve at the vapor canister that opens when vacuum hits it- when the truck is running. There should be nothing blocking the flow of fuel vapors to the canister. It probably has some crud in the line. The line runs up the back of the cab on the passenger's side before going to the canister.

Re: Blazer gas tank plugged vent tube at the tank.
 

Put a vented cap on it and forget about it.

Re: Blazer gas tank plugged vent tube at the tank.
 

Could be you are a victim of a mud dauber wasp.

Re: Blazer gas tank plugged vent tube at the tank.
 

I completely flushed the tank when we took the truck apart. The two 5/16 lines for the charcoal cannister are clear. The 1/2" vent to the filler is not... I could not push a coat hanger through it. I put a vacuum on it and nothing. I sealed up everything else on the tank and put 90 psi of air on one of the 5/16 lines. It caused the tank to expand and then pushed fuel out the filler neck. I soaked it in Seafoam before this.

It is completely and perfectly 100 % blocked. In the mean time I have routed the filler neck vent to one of the 5/16 nipples. My brand new fuel sender failed after the first full tank of fuel so the tank has to come out again. I will investigate more at that point. If I cannot get that one to vent I will tee the two 5/16 into the 1/2 vent line.

Re: Blazer gas tank plugged vent tube at the tank.
 

You can't fill it up with the filler neck vent blocked. After about a gallon of gas, it burps the next 1/2 gallon down the side of the truck.

Re: Blazer gas tank plugged vent tube at the tank.
 

Does the fuel filler neck match this one piece style? The vent at that end of the tank should just be an open tube no valve.

Re: Blazer gas tank plugged vent tube at the tank.
 

It looks just like that. But there is something in the tank vent. It is COMPLETELY blocked inside the tank. Cannot force a coat hanger in it and pressurizing it with my air compressor doesn't put any air into the tank.

Re: Blazer gas tank plugged vent tube at the tank.
 

SheepDip has your solution.

Re: Blazer gas tank plugged vent tube at the tank.
 

Maybe your gas station nozzles in TX are different than Kalifornia's but we have the vapor recovery type that vents your tank as it fills.

My avatar has no tank vent except the vented cap and I can fill it as fast as the pump will pump.