XJnine

1999 Jeep Cherokee sport 4.0 AW4

So I have been getting p0304 and p0300 CELs every once in a while. It seems to go along with rough idle at times. When its under load it feels fine. I'm riding on 37" tires so its pretty slow to begin with, never noticed a significant decrease in power. I decided that after doing some research on the forums I would try a leak down test and compression test. Here are the results:

LD.............C-D.C-W
#1 - 5%....148 160
#2 - 5%... 159 170
#3 - 29%..145 156
#4 - 41%..135 151
#5 - 7%....165 170
#6 - 8%....151 170

So as we can see from the leak-down, there are problems in cylinder #3 and #4. When doing the leak down, both cylinders had leaking out of the exhaust pipe. All cylinders showed minimal leaking out of the crankcase, it was barely noticeable though. I was planning on just buying a reman head from www.headsonly.com . Comes with valves and springs preinstalled for $345 shipped. I thought that until I did the wet compression test on cylinder 3 and 4. By the way, the wet test was done warm and with a capful of oil. Now I'm not sure what to think.

What would you guys do with this engine?

salad

Toss some Mopar Combustion Chamber cleaner in it first. Chances of carbon lodged in there is pretty high. I believe there's also a TSB related to weak valve springs. I'd do both of those before bothering with a head unless you had other issues like bad lifters too.

weebur

You didn't mention how many miles you have on the vehicle, or the state of tune. I'd start with cleaning the throttle body, don't forget that back of the plate and the IAC, both of which can cause idle problems and a complete tuneup. And, check your fuel pressure at the rail. Running some strong fuel system cleaner through the tank can't hurt.

There is a process of injecting water mist into the throttle body while the engine is running that is said to help remove carbon from the valve seats and combustion chambers.

The increase from dry to wet numbers on 3&4 indicate that you may have bad/broken rings. If that's the case and you can tune away the misfires I'd just run with it.

XJnine

There is 165k on the engine. It is a 0631 head. the IAC has been cleaned, there are new spark plugs, distributor, coil, and wires. All the simple tune up stuff has been done. I have also been running fuel injection cleaner on and off for a couple months.


There is an exhaust leak on #3 and #4. Just wondering if its worth putting a new head on this engine. Keep in mind, it runs fine most of time. I just get a rough idle when sitting at a stop light or in the driveway. Not all the time but sometimes.