I got a rough idle and codes P0300, P0301, P0302, P0455, and P1491. I'm trying to figure out what I need to do to fix it. my head casting # is 0331 but never had any problems. already done a combustion test and cylinder 2 had 59psi. already replaced spark plugs and coil pack. any advice is appreciated 🙏

 

P0455

The P0455 diagnostic trouble code appears when there's a leak in the Evaporative Emission Control (EVAP) system, and the system can't maintain pressure. The EVAP system usually consists of five main components: the fuel tank, fuel cap, vent valve, purge valve, and the evaporative canister (or charcoal canister).

p1491

https://www.google.com/search?q=jeep...t=gws-wiz-serp

 

The compression spec for the 4.0 liter engine is 120-150 psi with no more than a 30 psi variation between cylinders.

Cylinder 2 is very low and out of spec at 59 psi, if you have confirmed this with a second compression test, (you need to do this) you have an internal engine problem.

What are the compression readings for the other cylinders?