Hello everyone
I am having some problems with a 2011 Yukon 6.2L
Issue:
Finding gas in evap vent lines not tied to overfilling. Cleaned/cleared and it returns
very low fuel tank pressure readings (up to -4112pa)
p0451 code EVAP pressure range performance
difficulty filling tank
MID/TID test: $3d $c6 Purge flow monitor (min0 max60s actual 60.1s)
MID/TID test: $3c $c9 EVAP monitor (0.020") (min0ratio max0.727ratio actual 0.73ratio)
Things i have done:
New purge valve, checked closed with engine off and purge valve routing clear
New vent valve, checked open with engine off and vent valve routing clear, at least from can to filler neck
fuel pressure good
Charcoal can new, no clogs
I have not been able to check the routing from the fuel pump vent so its possible that its clogged.
Before i drop the tank is there any guidance on what is going on or what i should check?
Why would I be getting very low negative tank pressure? Why would fuel be getting into the vent lines even after i clear the lines and no gas has been added to the tank?
I got the updated version that has the outlet stuffed up near the filler neck opening. Not sure about a sock in terms of fabric. Might have had black plasitc mesh on the inside of the plastic cage.
Exactly which lines are you finding liquid fuel in?
Do you have the ability to get live sensor data? Can you hook up to the data link, key on engine off, remove the gas cap, and get a live voltage reading or pressure reading from the fuel tank pressure sensor?
I believe that the vent lines are co-joined at some point in the evap routing. The line that runs from the tank (fuel pump?) to the fill neck has a disconnect where it changes from plastic to rubber before terminating at the fill neck. That had fuel dripping out of it when I disconnected it. The plastic tube that goes from the back side of the tank into the mess of tubes and terminates at charcoal canister was wet with fuel when I removed it from the can. I can blow air into one of the mentioned tubes and a few mLs of fuel comes out the other.
I also believe that the fuel tank pressure senor might be bad. I am not sure if it is a wiring issue as I dont have any pressure versus voltage info. Any details on that would be great. Opening the gas tank with KOEO or engine running didnt seem to change the value. I also tried removing the tube right before the purge valve, no change in pressure. Some days its a dead line at -2k to -4k Pa, other days i do see it move with change in RPM and in positive values.
Just to clarify, -4112 pa seems like a lot of vacuum, but is actually less than one psi. No experience w/a 11 Yukon but my knucklhead diy’er ideas if my Corolla had these symptoms:
I’d remove the canister for look-see. I’d focus on the finding why the gas pump keeps turning off during refueling. In order to make room for fuel to enter the gas tank, the canister’s vent output path has to allow flow. Something may be restricting that path. Vent valve, vent pathway filter clogged, vent pathway piping pinched or clogged. It’s also possible the purge function isn’t doing enough purging, so the canister is clogged w/gasoline. Don’t know about yours, but on my car it is fairly easy to remove the canister, if very heavy, probably full of gasoline.
An HC tailpipe emissions test might be helpful too.
Do you have trouble filling the tank? Does the nozzle repeatedly click off before the tank is full?
KOEO and gas cap off, fuel tank pressure should be 0 or neutral–no pressure and no vacuum since the system is open to ambient are. The fuel tank pressure sensor reading should reflect this. Are you able to confirm this?
Yes
It is impossible to fill the tank. Gotta go super slow to keep the pump from clicking off. I suspect that if fuel is in the vent lines then maybe thats why i cant fill as it or something else is blocking the flow of air out of the tank and onto the fuel nozzle. Again the vent valve is open with key off. Hell, i can push air all the way from the back side of the hose right before the purge valve out the vent valve which goes through the charcoal can.
Charcoal can is new. The old one that i took off at the advice of my mechanic was fine. No clogs. New one is fine too, no clogs. Purge valve is new as is the vent valve.
Blasted out carbon bits from the vent tubing a long time ago so i dont understand the problems.
I can also confirm that i have negative pressure in tank with KOEO and running, gas cap on/off. The intermittent function makes me think it or the wiring is toast but it does not explain the other issues.
What is your definition of KOEO? Are the O’s on or off.
Fuel will vaporize and get into the vent lines and condense, even with a low fuel level in the tank. Have you replaced that rubber hose section that goes from the tank to the fill tube. They can get hard and no longer seal at the ends which will cause all your problems. When you replace it, make sure that the connections are clear and not clogged.
The hose from the vent valve just lays on top of your fuel tank, open to air. It is easy to pull down and check but it should not be the source of your issues.
You may need a new gas cap but that is not causing the hard to fill issue.
The Fuel Limit Vent Valve on the top of the tank is stuck or the FLVV line is blocked or pinched.
The fuel limit vent valve must remain open until the fuel tank is full, it closes to prevent overfilling.
Loose vapor canister particles can cause the fuel limit vent valve to stick.
Tell me more about this FLVV. It looks alot like the rear fitting on my gas tank. Do you know for the GMT900 if it is removable and replaceable? Would be great if i could swap it out with out having to drop the tank.