Well, last night I was moving a friend and we started noticing gas smell in the cab of my 88 pickup with a 94 22re. I was got under the cab and fuel was streaming from the charcoal cannister overflow. Now, I would expect this if I have severely overfilled the gas tank but I am sitting at probably a 1/4 tank right now...

The engine would run fine for a time but the cannister it would seem, was filling up with fuel. Then the engine would start to cut out and lose power, it would idle but not rev consistantly. Once I turned it off, the fuel would drain out of the cannister for a while, then dribble to a stop 5-10 minutes later. Not good!

I haven't pulled the cannister yet, however, this doesn't seem like something that the cannister should be able to do, especially with a 1/4 tank. Any ideas?

 

im thinking that theres some kind of block in the return line to the pump...

 

Hmmm... guess I'm not sure what you mean by return line to pump. Do you mean the return line to the tank itself that relieve the vacuum pressure?

 

There are 3 lines to the tank. One from the pump, one return to the pump and one vent.
Have you done any work to it lately?

 

Gotcha, I haven't worked on the pump or fuel lines yet. But sounds like its in order. What would be the best way to test that? Just trace lines, disconnect and blow out?

 

There's no real reason for fuel to accumulate in the canister. As mentioned the tank has 3 lines to / from the front: fuel pump output, pressure regulator fuel return to tank, vent from tank to canister.
The canister is supposed to store evaporated fuel vapors until the purge VSV triggers connecting the canister purge line to the intake manifold, sucking the vapors out of the canister. The fuel return and tank vent lines are near each other, which is why you were asked if any work's been done to the engine recently. If the fuel return from the regulator was mistakenly hooked to the canister, that would cause the problem you're seeing.

 

It's also possible that the purge VSV is sticking open or there are crossed vacuum lines which are putting the canister under constant vacuum and it's sucking fuel splash from the tank into the canister. But I don't think that's likely the problem 'cause I have the purge VSV vacuum lines temporarily connected on my 91 cause the VSV is broken and I needed the truck to have an operational vapor recovery system for emissions testing. Also the purge line is ported to throttle body ahead of the throttle plate (between the throttle and air filter) so it's not under constant high-vacuum.

 

So, in continuation, no work has been done to the truck, so I can't see any line having been swapped. I pulled the charcoal cannister and tested it per the manual and blew it out with compressed air and it checked out. Now, with everything hooked back up, I drove for a while and then pulled over and shut the engine down. I opened the hood and pulled tank vent hose from the cannister and blew in it. I was met with a lot of resistance and thought it was blocked. But presently it seemed to clear and then I heard it bubbling in the tank. I have less than a quarter tank of gas and blowing in the vent hose produces bubbling in the tank? Is this normal?

 

The sending unit that line hooks up to is probably sticking into the tank a few inches, I know mine is, because my carburetor was sucking fuel from the return.

 

So, what is the easiest way to get to the sending unit? Do you have to drop the tank?
Thanks for the input!

 

perosnally, id pull the bed off rather than drop the tank... but heck, what do i know, i have a hatch built in for pulling the sending unit...

BUT i have replaced one on a half ton chevy and pulling the bed took all of 30 mins and a friend to lift it...

 

Could also be the fuel pressure regulator. there is a vacuum line from that to the charcoal canister. fuel possibly leaking by at the regulator? much easier to get to than the sending unit in the tank. I'd check that first.

 

My truck only has one charcoal cannister, the one mounted by the passenger firewall, and it only has one vacuum line going to it, and it comes from the throttle body. Maybe you are thinking about the models that have two cannisters? When the engine is above idle the cannister is definitely under vacuum, but it would seem that the vent tube from the tank to the cannister has dropped down to low into the fuel... maybe