Fuel pressure problem with tank and miss

[bradp]

I went to meet anonymous user & 88_pacifica, & 3barmopar at the Indy get together tonight and here is the problem I encountered:

Drove about 30 miles everything ok then anything off of idle runs fine, but at idle has a bad miss and lope and smells like gas. I stopped at a gas station to see if maybe I had a plug wire off or something. Went to take the gas cap off and about blew my arm off with the pressure. I tried to put gas in it and the pump kept kicking off and wouldn't take gas, only got about 2 gallons in it to take it to 1/2 tank. Met up at the meeting point and still running like $hit at idle and light throttle but at 1/2 throttle and WOT runs great. Take gas cap off and still tons of pressure but none out of the Charcoal canister. Then sounds like a huge vacuum sound coming from the tank area. Went in and had an adult beverage and dinner. Came out seemed a little better, so i drove home about 40 miles. Still the same deal at light throttle and idle. Runs fine at 75mph on cruise and the traveler showed I got 22.4 mpg. Anyone have any ideas? Line broke in tank? Check valve in gas tank bad? Please help!!!

[Captain Chaos]

This may sound stupid and I don't really know what it would solve but maybe try not tightening the cap all the way to vent it that way. If you believe its an emmissions problem that would help narrow it down.

[bradp]

Left the cap loose at idle and still seemed to do the same thing.

[Clay]

well, the only way I can think of that you can pressurize the tank is if you have the tank vent plugged up, and then you are pressurizing it with the return from the fuel pressure regulator. Now on an L-body there is a vent w/ check valve on top of the tank, and then there is the fuel canister. The fuel canister can work the same way as well. What I would try is maybe running the car with the gas cap off, OR taking the line to the canister off and making it act as the vent line. See if either of those work, then that would tell you if my half arsed theory is correct!

[bradp]

Will try tomorrow evening, thanks. I think I'll checkfuel pressure too just to see what it does. When idling, I could definately smell gas too.

[black86glhs]

Brad, if you are getting pressure like that, it will smell like gas. Not saying it can't be a small leak, but the vent on my Caprice keeps coming off....the way I know is I smell fuel at the rear of the car. I would be real suprised if you didn't smell gas.
The only way this can happen is the tank can't vent and the return fuel is pressurizing the tank....as someone already said.
Not sure this has anything to do with how it runs, though.

[Captain Chaos]

Brad, if you are getting pressure like that, it will smell like gas. Not saying it can't be a small leak, but the vent on my Caprice keeps coming off....the way I know is I smell fuel at the rear of the car. I would be real suprised if you didn't smell gas.
The only way this can happen is the tank can't vent and the return fuel is pressurizing the tank....as someone already said.
Not sure this has anything to do with how it runs, though.

I would think that maybe if you pressurize the tank and the return fuel is slow going back it would cause a rich condition. But if you are smelling raw fuel I don't think that is so much a rich condition.

[black86glhs]

I would think that maybe if you pressurize the tank and the return fuel is slow going back it would cause a rich condition. But if you are smelling raw fuel I don't think that is so much a rich condition.

Hey!!! I didn't think of that. I think you might have something with what you said. I thought I read something on here about the better 255 pump supplying so much fuel the return was too small in some cases.

[bradp]

The fuel smell was pretty strong, I'll see what I can find tonight when I have a chance to work on it.

[Captain Chaos]

Hey!!! I didn't think of that. I think you might have something with what you said. I thought I read something on here about the better 255 pump supplying so much fuel the return was too small in some cases.

My L body was like that. I did a "quick" fix by running 3/8 aluminum line as a return, problem solved. When I put the new motor in that will be my supply and my 5/16 will become my return.

[88_pacifica]

Just got off the phone with Brad and he said that it threw a CE light with a code 13(map). He reset the computer and then it seemed to have smooothed out, but it still has a really strong fuel smell and it is seemingly runing really rich. He did say it's not pressurizing the tank anymore so this is a very peculiar situation. Feel free to throw out ideas/experiences with this sort of issue. Thanks....

[Captain Chaos]

When my vacuum line has come off the MAP it ran real rough and real rich. I'm assuming he's checked for actual fuel leaks to eliminate that as the smell problem.

[black86glhs]

Possible that the map took a crap.

[bradp]

Ok, changed the gas cap after talking with Chris @ TU. Runs much better and no hissing sound from the tank. Other than checking my fuel pressure that is the only thing I touched. Now the thing boosts like mad WOT it boosts 16 psi the when it shifts it creeps up to 20-21 and even on tip in throttle it'll go up to 19-20. I tried a grainger and does the same thing. I think I'm going to re-do all the vacuum lines (even though I did all new lines stock looking)and put the vacuum block I have on it. I wanted to look stock but at this point F&*k it!!