QuestionWhenever I fill up my fuel tank, I have to nurse it. The fule pump continually clicks off like the tank is full. This happens when I first start filling, so I have to gently hold the nozzle handle. This happens at every fuel station I go to, so I know it is not the nozzle. Is there an air line or filter that can be clogged and how do I correct this?
Thanks much
AnswerPresuming your car is model year 1998 or newer, you likely have a blockage in the venting/vapor management system for your fuel tank. The problems could be:
1. twisted or crimped hose or pipe
2. damaged fuel tank preventing proper fuel flow into tank
3. stuck shut fuel cut valve
4. faulty or fuel-soaked charcoal canister
5. clogged canister filter
6. stuck shut canister close valve.
If you're not familiar with this system, it may be best to have it professionally diagnosed, but I'll give information below on how I typically locate the problem causing the issue you describe.
Is your check engine lamp on? If so and you have trouble code P0446 or P0449, the problem is less likely to be issue #2 or #3.
First, check visually to make sure all the vapor plumbing is in place, in good condition, and not crimped or kinked.
I typically diagnose this issue with a scan tool reading the fuel tank pressure, or if that data value isn't available, just a voltmeter measuring the voltage signal at the fuel tank pressure sensor signal wire. Then, while the purge control valve is cycling, I'll start at the canister filter and begin disconnecting items up the line until I disconnect the one that releases the vacuum in the fuel tank. Next after the canister filter would be the canister close valve and then the canister. If disconnecting one of the items releases the vacuum, then that's the item that's causing your issue.
If the purge valve doesn't cycle enough or doesn't draw enough vacuum, you can bypass it and just attach the purge line to the manifold, but be careful if you do this. Manifold vacuum can suck the fuel tank shut to the point where it's damaged.
