TheNovaMan

My '00 Cherokee Sport misfires at idle when I start it hot. Throws P0300-P0306 codes, except for cylinder #1. It did this just a little bit every once in a while, but all of a sudden today it's bad. Foot to floor, and nothing changes. It usually clears up and then runs fine, but it stalled twice today. 153k miles. I'm thinking check plugs, then injectors?

DFlintstone

I'd agree that with a miss, making sure the plugs, cap, rotor and wires are all spiffy would be where to start. (even new plugs should be gaped .035) Any issues with coolant missing or overheating?
Also take note of the color of the plugs and keep track of which was which, (ie. #1 was white and #3 was black....)

TheNovaMan

It's a 2000, so it's distributorless. Are there still plug wires, or does the giant coil snap directly onto the plugs?
There hasn't been any overheating, but I haven't checked the coolant level.

DFlintstone

Oh Duh! (I knew that). Was distracted..for good reason. The 2000 has the infamous 0331 head, prone to cracking, and it's not rare to throw a mis-fire code because of it. "misery coolant loss" is a symptom. Hey you are likely fine, just check the plugs!

Guess it's a doubly good idea for those years, (00,01), to be sure you don't overheat. You really don't want to blow a hose, and for sure shut it right down if it overheats. "I drove on home because I was close..NOT!)

TheNovaMan

Holy gap erosion, Batman! I think I found the problem: the gaps opened up to about 0.070 inch! Fortunately they were nice and clean, so I squashed the ground straps down to 0.035 inch and that helped tremendously. Then I went to the parts store for some Champion coppers. Is RC12ECC the factory heat range? (They cross-reference to Autolite 985, which is what was in there.)

caronaxtr

I have the same issue, Biggest problem is that in New York, to pass your yearly inspection you can't be throwing any codes. Mine does the same exact thing. DRIVES ME NUTZ! Did gapping the plugs correctly help? Did your check engine light go off (if it was even on)?

DFlintstone

Well done! Yea, even parts with no moving parts wear out...

TheNovaMan

It turned the check engine light on, then I gapped the plugs, and it turned off. It still misfires a little after hot starts, but not enough to turn on the CEL. I plan on installing the new plugs tomorrow, and I expect the misfire will be completely gone then.

xcalibur_123

I have the same problem, but I changed spark plugs already and stopped for a couple of weeks then it's doing it again, :/

Is it true that platinum spark plugs don't need calibration??

DFlintstone

I've seen platinum's that had the outer ring as the ground electrode. I don't see how you could gap that. Any conventional type could have been dropped or set different than 35. There were 0331's on 2001 as well btw. Good to be sure missing coolant isn't in your oil causing wear that can really ruin your day.

Forum, anybody, wouldn't a small coolant leak/crack leave the porcelain on that plug clean as a baby's butt? Maybe not.

xcalibur_123

No, thank God I don't have coolant in the engine, but its really weird that shaking, btw it only does it when I have run a while and it's really hot, I live in south tx and temps here hit 100+ f.

CMAHON

my 01 does it all the time in all temps. changing plugs and injectors (784 swap) this weekend. will post if it helps or not.

TheNovaMan

According to the reading I've done, Jeeps don't like platinum plugs.

TheNovaMan

How did it go?

CMAHON

Update: got the swap done, changed plugs (.035 gap), new filter, and flashed my ECM. My idle still sucks. and no noticable difference. still runs even crappier when shut down and restarted.