Sorry, I have to correct our reply: this function can't be supported. And also no schedule to develop it at present. Sorry for the confusion.

Sorry for my mistake. I have corrected my reply above.

 08 dodge nitro no bidirectional on evap vent valve? I can't find it.

                  The atmosphere vent is located on the ESIM just cap it,pinch it whatever. Easy way to find it is pump smoke till you overcome the check valve.ESIM is normally closed engine off without excessive pressure

                    Hope you have access to All-Data if so there is a pretty good detailed explanation about ESIM operation and the two internal check valves that are normally closed engine off. It's supposed to be integral to the canister and if I remember correctly (been a few days) the electrical connection is really just a diagnostic switch much like a leak detection pump configuration but check. In my mind if I kill atmosphere at the ESIM and also purge to the intake then smoke everything gets tested tank,plumbing etc. if it's not leaking through the unplugged purge back to the intake I think your only left with a possible malfunction of the ESIM or it's diagnostic switch. Hope this helps and good luck