2000 XJ missing?

No, my truck isn't physically missing...

My engine on the other hand I believe is; heres why.

When my truck is running and you stand behind it, you can hear little "poofs" from the exhaust I guess you could call them. Sounds just like when and engine has a misfire...little hiccups in the exhaust.

When my trucks running (idle) and I stare at the tach...I watch the needle bounce up and down(no more than like 50-100RPM at most)

But...it doesnt throw any codes? I believe this is the key to my fuel in-efficiency(aside from the obvious, being a Jeep...) as I only get 400km/tank, half of that is highway. Seems really low. Ever since I've owned the truck it's done this, but never thrown codes. So I've decided to post about it. If I have just enough things pulling juice on, the bob of the engine RPM is enough to make the voltmeter bouce from 9 to 12 volts.

I've changed the plugs myself twice, in the 30000km I have owned it, and I dont abuse it(yet). It's still a stock XJ with 177,XXX km on it...I had NGK plugs, did some research and found Champions run 'best' in 4.0's. I now run Champions @ 0.035"

Anyone have any thoughts?

Thanks.

ps. the miss is NOT evident when driving, in fact can not feel it at all, so I'm lead to believe it's just at idle or my timing is just a tiniest bit off?

If it was actually "missing" it would throw a code, or at least store a pending code (does not make CEL come on). I do think though that the plugs come pre-gapped for cherokees if you go to the parts store and ask for them by year make model of your vehicle...which I think is 0.030 not 0.035....I doubt that's your problem, but just throwing that out there.

As far as timing...you cannot adjust it...computer controled.

As far as gas mileage...that's not that bad...I did the math and thats about 254 miles to 19 gallons which is a little over 13 miles to the gallon. Not great, but it depends on how you drive too! I know when I first got mine, I couldn't get 300 miles to a tank to save my life and it had some spark knock at lower rpm's with a heavy load....now that I run premium gas (93 octane here) I get no less than 330 miles to a tank. For those people that say Premium fuel is too expensive to run...it's really not. It's only like another $4-6 per tank and I get A LOT more mileage out of it! Actually saves money in the long run!

Check for vacumm leaks.

Even though you just changed the plugs, I'd check them again. I had a similar situation with my 2000xj. It turned out that one of the plugs that I had put in developed a crack in the ceramic coating and was likely shorting through the block. I won't use Bosch plugs again.

Also, when I added a heat shield between my intake and exhaust as shown here, my idle smoothed out substantially.
http://www.angelfire.com/my/fan/manifold.html

Here's a different approach to the same problem.
http://www.go.jeep-xj.info/HowtoIntakeShield.htm

Good luck

This is similar to my problem. 98' XJ 4.0 125k. In January I had a code for misfire, changed the plugs and wires. Thursday I noticed the same problem and it was a misfire code again on cyl. 6. Today I changed the wires and checked my plugs and put on a new distributor cap. My main problem is I just started a new job, I am supposed to pay first month's rent and move into a new apt. tommorow(Saturday) and I am having to borrow money to do that. I have a pretty good multimeter I bought on clearance but I don't know how to use it really. If there are any solid idea's, I can get to a Jeep junkyard not too far away. I have limited time and experience which makes for a bad combination.:explosion From reading the boards, it appears I need to change the distributor or fuel injectors or any # of sensors. I need the cheapest alternative or reassurance that I can make a 2 hr round trip pulling a loaded trailer. Thank you in advance for any help that can be provided.

Daniel

There is no distributor in a 2000, it's a coil-on-plug configuration.