Hi-psi

I'm having the common slow to fill the fuel tank problem, likely caused by the previous owner(s) regularly overfilling the tank. I'm going to be replacing the EVAP canister soon, and although the recommended practice is to use some compressed air to blow out all the charcoal pellets that may have accumulated in the EVAP lines I'm also considering just to be sure simply replacing the lines all together.

For the 2008 model year, I've come up with two part numbers and I'm looking for some help/insight in determining which I need.

Part # 25860206 (or 25801698) is listed as fitting 2007 and 2008 vehicles with "fuel tank with external vent inboard of MRA".

Part # 25914595 is listed as fitting 2008 and 2009 vehicles with OUT "fuel tank with external vent inboard of MRA".

So, it appears it could be either for a 2008 model year, with the determining factor being whether the fuel tank has or doesn't have an "external vent inboard of MRA". Any clue what that means? As best I've come up with is "MRA" stands for Module Reservoir Assembly, so I'm thinking they are referencing the fuel pump assembly and whether or not it has an external vent? If so, how do I determine that?

Part I'm referencing is item # 1 in the attached diagram.

Thanks in advance for any help, insight, or information.

tech2

the dealer parts department gotta know which line is for your build. try more than one dealership.

that is a pretty short line to blow out. That is what i would do if I found pellets. did you find pellets in that line? Anythings possible but I would think that would get drawn up the purge line; not flow against purge flow into the tank line.

if the purge line was blocked you would be getting purge flow codes....are any set?

the tank has to vent out the tank vent to the canister, out the vent valve and out the vent filter....make sure all those line and filter are clear.

Hi-psi

Well, to provide a bit more info...

Just picked up this Denali about 2 months ago. It had a little bit of a miss at idle and below 2000rpm which I figured was just plugs/wires. Also occasionally would get the "Tighten Gas Cap" message in the DIC and a P0455 code.

So, I threw a new set of plugs and wires on it, discovered the PCV tube from the top of the intake to the back of the driver's valve cover was leaking, replaced that, threw a new OEM gas cap on it, replaced the EVAP vent valve with the updated style, and also threw a new Bosch fuel pump in it as a few similar problems found on various forums indicated the top of the fuel pump assembly as a potential problem/leak area. Plus, figured not a bad idea anyways to replace the pump given the miles on it. Thought that had fixed it, but a day or two later it went back to setting the code/message and the stumble. Also, the hard to fill issue didn't really manifest until the fuel pump replacement. I'm pretty sure the fuel pump assembly/lines were leaking (there was some corrosion on the top and metal 90* lines), so maybe it was leaking enough that the tank pressure wasn't building to the point of keeping fuel from filling. Now that there's less of a leak, I'm having the hard to fill issue. So, I have a new EVAP canister and purge solenoid (up behind the alternator) ready to install. I'm limited on where I can work on the vehicle and don't really have access to compressed air to blow the lines out, so I was thinking maybe the better fool proof approach was just to replace all the lines in the EVAP system (not just the ones I'm asking about) to ensure everything is covered.

The lines I asked about are the only ones I couldn't nail down a for sure PN on.

In parallel with this all, I'm also lining up trying to borrow a friend of a friend's smoke machine to do a smoke test on the vehicle to see if that gives any idea to the source of any potential leaks.

tech2

clear the code and see if it resets. p0455 sets when the sysem leak test and can't achieve or maintain vacuum. if the code resets, check the fuel tank pressure sensor. it should read 0"h20 with the engine not running and the fuel cap removed. Running, cap on with the system purging...you should see a pressure drop as the system draws vacuum.

2007LTZ

Thank you for the information you provided about the 0"h20 in the gas tank and less when it is idling. I have a scan tool, both see -2" h20 but I still have a dumb P0455 code. Thank you for providing that information, now I know what the reading means.