CClememsom

just gonna throw that picture out for the crowd, im sure theres millions of thread about these exact same issues but I can't find anything that quite matches up and fixes my problem.. so let me give yall the run down

This is a 2001 jeep cheroke 4.0 I6
​​​​​​recently bought, came with the check engine light, checked it when I got it home misfire blah what ever free jeep is a free jeep. So far I've changed the coil pack, there are no spark plug wires.. spark plugs, I've been down the whole spark plug rabbit hole I'm running ngk coppers gapped to 0.035 I've did a compression test and I believe the 6th cylinder was kinda low I don't recall the exact reading.. ive been chasing the evap leak can't find that, figured it may be the cause of all evil may be unrelated may not be evap leaks tend to cause trouble... daily drive this hog everyday doesn't seem to miss when I've got some rpms, doesn't go into limp mode, it will miss if I'm slowing down sometimes, sometime the cel blinks sometimes it doesn't it has no consistently. Decide to bring this topic to thousands of other people who are most likely smarter than me and know what's up with the 4.0s... lmk on a slim budget 😂 arnt we all?

tech

Did you check the plug that goes to the coil packs ? and for the evap system I had to remove and clean all the hoses where they hook up to the evap and then put some clamps on the hoses and that fixed it .

bluejeep2001

Sadly your misfires could be almost anything...have you checked fuel pressure. If you have a graph mode, how is the o2 sensors sign wave. A crack in the exhaust manifold above the sensors could be an issue but you usually cant see it without removing the intake. . For your gross leak issue...on your drivers floor where the floor ends and turns unto the engine bay firewall there several 1/2 ish hoses that make the bend as a combination of hoses and plastic tubes. These hoses swell with age and then dont make good connections with the tubes. Not easily accessible and usually very dirty and greasy. A couple of tywraps on them fixed the long time leak issue on my 01.

gkucera

I'd do a leak down test. Will tell you if you have burned exhaust or intake valve(s), or bad piston rings.

BruceB

P0455...maybe a new gas cap?

third coast

Yes, definitely give that a try. The large o-ring on the gas cap will often get hard or crack and not seal properly. Otherwise if there is much rust in general check gas filler metal pipe (often exposed to rear tire kick up debris), gas tank, and emission lines as previously mentioned.