#4 Misfire

I have a 2000 Cherokee (4.0 with the coil pack) with 127K and i notice sometimes it idles a little rough and does not seem to have the good power that my brothers jeep has. i cleaned the throttle body, put new plugs in a little while ago and it still acts the same. I checked the codes with my buddys super expensive scanner (the check engine light was not on by the way) and it said i have a #4 misfire once in a while (that i believe causes it to idle roughter). i dont think it kicks the check engine light on because it is not a constant misfire. I was driving it the other day and i it started skipping very bad and did kick the check engine light on. I got it home and it had the #4 misfire code. I changed the plugs with champions rc12ecc plugs (or whatever it said under the hood on the catylist) so i know it has the correct plug that jeep put in. before i had some other champion plug in there that advance auto gave me that said it fit my jeep. so that got rid of the skip with the new plugs, but it still lacks on the power and dosnt idle smooth. here is a quick run down of what i have... K&N filter, compression check turned out good numbers, tried 3 different coil packs (one i have on there from the junk yard now looks real good), put the correct plugs in it, cleaned the throttle body, tried different brands of fuel and grades, swapped in a different junk yard computer. my question is what else can make this #4 misfire happen? crank position sensor? injector? fuel pressure?

If it's #4 cyl misfire, there is a good chance that is is something that only affects #4 cyl. Fuel pressure and CKP should be related to all the cylinders. Injector is only that cyl. Seems like injector is likely candidate. I see you checked compression, which should help eliminate internal engine problems, but sometimes it takes a cyl leakdown test to really show all issues. I assume your are aware of the problem '00's seem prone to of having microcracks in the head between the #3 & #4 cylinder. Symptoms of this are steady consumption of coolant and a milky residue on the bottom of the oil fill cap. To find out more search "0331 head". To check out your specific issue, why not swap the #4 and #1 injector and see if the code moves?

winterbeater said:

To check out your specific issue, why not swap the #4 and #1 injector and see if the code moves?

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x2. start it, pull the fuel pump relay to bleed off fuel rail pressure, drain the rest from the schrader valve and then swap injectors.

As for plugs I would recommend NGK. I found that my 2000 ran better with them then the champions and the FSM specs them too.

i just fixed a #4 cyl miss fire in my moms cavelier. it turned out the spark plugs were toast. make sure you are using the plain jane champion plugs. my 99 dodge ram had a rough idle caused by corrosion in the spark plug boot on two cyls. how did the plugs look when you replaced them? any excessive or unusual deposits?

Does the #4 Misfire come up after a Hot start?
If yes check this out.
http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf

I ended up wrapping #3-4-5 injectors & the problem is gone.

garr said:

Does the #4 Misfire come up after a Hot start?
If yes check this out.
http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf

I ended up wrapping #3-4-5 injectors & the problem is gone.

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That TSB is actually for a #3 misfire. I think he is chasing something different.

All the champion spark plugs i took out looked the same, a slight tan to the porcilin, nothing out of the ordinary. I did not have it pluged into the scanner when the engine was cold, but you can still feel it skip when i start it up cold. i feel the skip just sitting in the seat in park, and its not running 100% smooth. Maybe i should swap injectors or get some from the junk yard and only replace the #4 injector. My theroy is, if its not a constant misfire, maybe the computer is just dealing with it and the O2 sensor is messing with the mixture and yada yada not giving me full power. Another observation i have is the shift points seem wierd. I could be under light acceleration on flat road and it does not shift as soon as it should and at a slightly higher RPM than normal. And yet another observation, when i pull my trailer up my hill, the engine does not seem to want to rev higher than 3000 rpm. It will if it kicks down into second, but it should still be fine in 3rd with the converter unlocked. I dont have an O2 sensor downstream, so im not sure what shape the converter is in either, it dosnt sound plugged or anything. What are the chances it could be my TPS or MAP sensor or the thing that in the distributer hole?....sorry, i dont know what that does...obviously timing like a resolver or something. I know there is a way to test them but i havent done anything with them. my gas milage has been decent. I have been getting about 21.5 on the highway driving 55mph. I dont drive fast, its a jeep not a race car P About the cylinder head, i knew there was a less desirable head out there but wasnt sure if it was my year or not. Where is the casting number? I appriecate ya'll helpin me out on this!!

The not shifting correctly seems like a TPS.

oh i forgot to elaborate more on the shift points....im thinkingif i had a misfire that is causing me to lose power that is going to affect the the engine vacuum and maybe the transmission shift points are based on vacuum as well as speed. Kinda like a Turbo 350 Tranny. Maybe ill try swapping in a different injector and see what happens. I know i have a misfire problem and ill fix that first. There have been some rare times where it seems to run real good like its supposed to, but that hasnt been lately and the shift points then were good.

Wildchild467 said:

maybe the transmission shift points are based on vacuum as well as speed.

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Not on the AW4