I have a 2001 5.9L 4x4 Extended Cab, it has had a check engine light saying "Large Emission leak" since the first time I took it off roading. I've been diagnosing everything I can and I think I finally found the problem: I crawled up under my driver side fender where I can see the top of the gas tank and I noticed a little hose (about 1/4" thick) disconnected from the tank. According to my Hanes manual it is the rollover valve connection where the fuel pump is. I reconnected it but it is kinda just hanging there. All it is a hose with a plastic piece that doesn't even seal up against the connection. Its really lose and I can jiggle it off. Is this how it is built to be? or does it need to be replaced? I can smell gas when I turn off my truck in the afternoon and the local shop quoted me $80 just to look at it so I would like to fix it myself. Any help or links to buy a new one will be greatly appreciated. Thank you!

 

i've been chasing a P0455 for a long time. i've cut the split ends off numerous hoses at the purge solenoid on the passenger side front fender. also replaced some split hoses at the evap canister under passenger side.

i've not looked at my rollover valve, but it sounds like it should be my next contortion. the hose should fit tightly over the nipple, and its job is to route evap vapors to the canister. inspect the end of the hose for being split, and if so, either cut off the split end or replace the vent hose. its just vacuum line.

 

I'll tell you how the evap system works so you can better trouble shoot. A large leak is generally a bad gas cap,but not always.

The Evap system is for vapor recovery,but the system check is done by the computer by acctually pressurizing the gas tank to 1psi. This first checks to see if there are any leaks,hence the gas cap being bad won't hold the pressure if the check valve is bad.

The way the computer knows if there is a leak or not is by counting the number of pump pulses it takes to pressurize the tank at a given fuel level off of the fuel level sender. A bad fuel level sender or one that reads incorrectly at a couple spots will cause a leak code also.

 

I can second this every time I get gas when i take the cap off it lets out the pressure.

 

This has perked my interest because I think this is the code I keep getting from time to time. Do you guys have symptoms when you drive because of this problem?

 

no ill effects nor symptoms to the engine or driving.

its just an emissions check, also a safety check to contain gasoline vapors which could explode in an enclosed space such as a basement or garage with a gas furnace or hot water heater.

 

By the time you get the code, it's happened three consecutive times. The main time for the computer to run the check is within 2 mins of start-up. This is when vaccum is applied to the vapor canistor to remove the collected vapors from the last run time,which is not uncommon for it to give a rough idle right after start up,although slight for a few seconds.

Then the pump will kick on. This with the purge solenoid is located on the passenger inner fender. It has the little filter with in it to keep the air clean being pumped into the gas tank for the EVAP test.

Like red said,if it had just checked and you pulled the cap it could have pressure. If it has vaccum at the cap,that means the gas cap isn't allowing air in,which isn't good either.

As far as driving issues with the code,it will over time make a noticeable downgrade in performance,as any MIL will, just to make sure that you get it fixed.

I say that, because I've been metering when a computer goes from mid level emission ready to a full green, and it makes a very noticeable gain in performance.

 

its weird I have only gotten the CEL with that code a few times, and everytime it came on when I punched the gas hard. It light up right as I did that.

So when should I have pressure at the gas cap? Right after I shut it off from running it? Should there be pressure after the truck has sat for awile?

 

The only time you would notice it is if you happen to pull the cap as the self test was being done, or say parking in a lot in the morning when it was cool and then pulling the cap in the afternoon when it got hot out. Like a gas can that sits in the sun.

The tank heats during the day, vapors build, the gas cap will only allow air into the tank and not out. You start the truck and the computer purges the vapor canister and relieves the pressure in the tank.

The self test will only perform after there is no pressure in the tank. As you burn gas and the level drops, the gas cap allows the air in so as not to cause a vacuum which could cause fuel pump issues.

 

well i think i found the problem. The nipple that extends off of the rollover valve was cracked and inside of the connector. Took the guy at bennet auto a glance to figure that out.