fuel tank over pressurized

[mack]

ok, I've got a weird problem I've read a few posts relating to it but none seem to be exactly the same problem? I just purchased a 1994 f350 idi turbo and im getting an absurd amount of pressure in the rear tank. when I remove the fuel cap it expels a high volume of air and some diesel, I was driving it home and filled the rear tank and it pushed fuel out of the filler neck the pressure built up enuff that it blew an injector return line off and the fuel continued to come out of the return line even after the truck was turned off untill I undid the fuel cap and relieved the pressure in the tank what could possibly be the cause of this the front tank is empty so it can't be taking from one tank and returning to the other also the pressure builds up as soon as the truck is started no matter how much fuel is in the rear tank ? any help would be appreciated

 

[79jasper]

You have a injector stuck open.

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[mack]

thank you, ill check the injectors didn't realize that an injector could do that but at the pressure they are running it makes sense now that I think about it

 

[OLDBULL8]

Check the vent on top of the tank, it has a rollover valve on it, the hose should be a couple of feet long.

Change the fuel tank cap to a vented cap.

 

[mack]

i will check that aswell thank you

 

[madpogue]

Which tank did you have selected when this happened? Does it happen when you select the rear tank?

 

[mack]

yes i was runing on the rear tank the front tank is empty

 

[Agnem]

You have a injector stuck open.

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If you are implying that exhaust gasses are getting into the tank through a stuck injector, I'd have to say that I don't think that is possible. For one, the hot gasses would melt the return line and cap. Two, the injection line would burn the paint off of it, and lastly there is clearly a tank vent problem, as you should never have an issue with venting pressure when removing the cap if the tank is properly vented. The fact that the return line blew off, and there was fuel coming out of it while the engine wasn't running, seems to indicate that you have a cross over situation in the tank selector switch combined with an improperly vented tank. In order to build that kind of pressure in the tank, more fuel would have to be returning, then is leaving, and the only way I know that could happen is if the tank selector is plumbed incorrectly, or the FSV valveing is broken.

 

[79jasper]

Could be. But for that much pressure.....
I don't know. Was just the first thought that came to mind. Lol

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[madpogue]

Put some fuel in the front tank and switch to it, and see if the problem happens on the front tank as well. If it does, then it may inded be something going on "up front", with the fuel return or whatever. If not, most likely it's a tank selector issue, where it's drawing from the front tank and returning to the rear.

Are you certain there's no fuel in the front tank, or are you just going by the gauge?

 

[mack]

The front tank was completely empty verified by tapping on the tank and the truck wouldn't run on the front tank so I checked the injectors previous owner said he thought the passenger side rear was bad so I pulled it out and it came apart in two pieces obviously it was no good lol I replaced the injector with a spare I had and it seems to have fixed the problem so far, I will fill both tanks to be sure but so far so good thank you all for your help