Trouble with fuel system, I think..

[Josh1989]

Hi all, I'm new to this site but figured it might be a good place to look for answers. I have a 2015 Chevy 1500 LT Z71 w/ the 5.3L non-flexfuel. Recently my truck has been giving me trouble. When I remove the gas cap the engine dies along with what seems to me an excessive amount of vacuam. Also when I fill up I have to try to start it 3-4 times and even then I have to feather the throttle and keep the RPMs hi for about 30 seconds. It only happens when I fill up other than that it runs perfect. No engine codes. Any help would be greatly appreciated. Thanks.

[Supreme Pizza]

Uh..... No idea man. Maybe something to do with the fuel pump / fuel vapor system? The only thing I can suggest, is to replace the gas cap and see if that helps.

[Supreme Pizza]

I guess you could put a fuel pressure gauge on the fuel rail, and monitor fuel pressures during the trouble event. The port is near your injectors.

[Josh1989]

Appreciate the info.

[txab]

First step is to have have any stored codes read. Most parts stores will do this free of charge

[Josh1989]

No codes to read

[x219c]

A complete guess... but it sounds like the valve is getting stuck and not allowing air into your tank. No air to replace the fuel makes the pump work harder.

 

Though, my theory goes down the crapper if you’re filling while it’s running. That should be an infinite supply of air.

 

 

Sent from my iPad using Tapatalk

[Supreme Pizza]

Any update?

[Pearl2017]

Are you sure it is vacuum in the tank and not pressure? if the cap doesn't hold pressure in the tank you will get a code. Every now and then the wife's G8 gets a CEL/code and I go out and tighten the cap. But it is Pressure that needs to be in the tank.

 

If it is pressure then the loss when you pull the cap is having some effect on maybe a weak pump of a clogged filter? As was said a pressure gauge on the fuel rail will answer that question.

[Supreme Pizza]

Alight .. here goes.....

 

 

 

One way to verify that it is a fuel problem:

 

Have a buddy remove the fuel cap while you assist the engine with starting fluid. If it will stay running, at least you know for sure that its a fuel issue. Next, you could "vent" the fuel system through the service port on the fuel rail to see if removing the gas cap causes a drop in fuel pressure. Then you could put a volt meter on the fuel pump lead wire and remove the cap to see if the loss of fuel pressure is a result of voltage drop, if not- then perhaps its the fuel pressure regulator somehow being effected by the pressure in the EVAP system. The next steps would be dependent on the results of those tests.