So back in November I bought a 1996 Cherokee 2 door at a city auction, previously owned and maintained by the city of Houston. 117,8xx miles and in great shape for the most part. I know the head was replaced back in 2002, from a note in the manual and I see a handful of aftermarket parts here and there that likely wore out over the last 20 years or so.

two months ago it started to idle very rough, and over time the issue got worse and worse until it gave a misfire code on cyl 1 and 3 (P0301, P0303) and it became harder to start. I changed the distributor cap, rotor, spark plugs (they looked bad, especially 1 and 3) and the cables. and a week later got a P0300, random misfire. Last week I gave it the seafoam treatment (in the throttle body and the tank) and today its giving a P0300, P0301, P0303, P0305. I'm starting to run out of ideas as to the cause of the issue.

Didn't pay much attention to it at first but my front and rear PCV valves have a lot of black crud around the grommets, even though I cleaned them up not too long ago. The front one fits very loose and has a slight gap. The entire valve cover has a layer of baked on crud so it didn't seem particularly special if the grommets were too. Could this be the cause of a larger issue leading to a misfire? I don't have the cash to take it to a mechanic but I'm handy with a socket wrench. Any DIY fix would be a lifesaver!

 

Rodents have a go at the injector harness?

 

Check the fuel pressure.