Recently, after fueling up my 2004 Suburban, it would not start. After trying it only once, I took off the gas cap and it started (although quite weakly). Since then, I have had to do this after every fill-up. All the starts between fill-ups are fine. I tried fueling up and not quite filling it (probably a little more than 3/4 full) and it did the same thing. About 2 months ago, I installed new plugs, wires, air filter and one oxygen sensor, but no work recently. The engine light has been on for some time, but I figured this might be something with emissions. I do not have a code reader.

Any assistance would be greatly appreciated.

 

Welcome to the forum.

Most auto parts stores will scan for free. Be aware that the DTC(s) will not necessarily tell you what part is bad but will point to the area of the problem. There are extensive troubleshooting fault trees in the factory service manual.

 

Remove the gas cap, look down the filling tube and see if that little metal flapper is gone. If it is, that's your problem. If it's not there, it's sitting in the bottom of your gas tank. When you fuel up, it's getting flushed down to where the fuel pump draws your fuel from. Same thing going on with my 07 Hoe. Check engine light is on and every now and then I'll get a TIGHTEN GAS CAP message. It'll show up as an emissions code because with that flapper gone, excess fumes are escaping. Let me know if you find it gone.

 

Working away so it took me a couple of days to see your suggestion. Thank you.

I went out just now to check and the flap is still there. Unfortunatley I had it in and the mechanic replaced a vapour selenoid and a filter canister of some sort to the tune of $500. When I went to fuel up it still wouldn't start until I took off the cap. I called him and he's going to look at it again.

Puzzling - thanks for taking the time to reply. Any other ideas welcome.

 

Check the fuel pressure also... I wonder if some kind of vapor lock is happening keeping the fuel from being siphoned from the tank....
I'm thinking there is something up with the fuel pump....

 

Is there any p[ressure in the tank when you remove the cap?

 

DO NOT change fuel pump. Tried that and problem still there. We need answer too!

 

We also tried small amounts of fuel without issue but over $50' problem is back. Backfired and won't catch. Then eventually, weakly, it does catch but it doesn't want to.

 

I have had the same problem with my 2004 suburban on the last 3 fill ups. The fuel pump is less than one year old although that doesn't really mean anything. It seems like it must be a vacuum issue or fuel cap. It seems worse if I remove my cap though.

 

remove the purge solenoid evap line and see if you can blow through the purge solenoid. You should not be able to.


If you can blow through it, every time you fill up, fuel vapours from the tank will flow through the evap canister into the throttle body and enrichen the fuel mixture creating a flood condition.


You could also remove the evap line at the purge solenoid before filling up. If its starts normally, this is the problem. this fault should set a evap leak dtc and turn on the ses light.