Hello all,

So this issue of mine has started about 2 months ago. truck is an 07 NNBS 5.3 LY5

I turn the truck off and remove the gas cap. I proceed to pump fuel into the tank and then put the gas cap back on, get in and first attempt the truck fires then turns right off not even getting 2 revolutions. Try to start again and it tries to turn over but after 5 sec of the starter turning and intermittent fires it finally fires up and runs fine.

The truck acts like theres a vacuum leak but once it creates vacuum it works just fine.

I have no codes when this happens and no pending either. Last year I got a P0442 which is a small evap leak. I replaced the solenoid under the truck and the valve at the engine. I still randomly get the small evap leak code but it can be a few weeks between the times i get it and there is no repetitive code set after getting gas. It also does not matter if I fill up, or get half a tank.

My only other thought is the map/pressure sensor on the tank not functioning right and not telling the ECM that the tank has been recently vented and when I go to start the truck, the engine pulls a vacuum on the tank and all that air not being regulated by the maf cause the truck to act like a vacuum leak is occuring. I replaced the gas cap when I did the solenoid under the truck.

Last March I replaced solenoid/gas cap under the truck. I replaced the hoses that go from the canister to the solenoid under the truck as well and those clamps are tight and not leaking. June I replaced the valve at the engine. Mid July I got the small evap leak code again and maybe once a month i got the code. Mid November is when the truck started acting up after removing the gas cap.

Sorry for the long post. Anyone have an idea? Am I on the right track or perhaps maybe one of the valves i replaced is malfunctioning again.

I have an Autel (which is like a tech2) i can borrow whenever so if theres a procedure known to run so I can test the evap system, let me know. I used the autel to tell me what airbag sensor was bad, among many more fun things.

Thanks in advance for any advice.

 

Does it do it only when you get gas or can you just remove the cap in your driveway and it still does it?

 

Try turning off all your evap codes and see if it continues

 

Anytime i remove the cap it does it.

Ive cleared codes everytime they have come up. Code sets dont appear to be linked to the issue on a time base. As in, the code set is random. Anytime i open the gas cap is when i have the hesitation