Rough Idle and CEL at Quarter tank of gas, every time!

I have 2000 Cherokee Classic 4.0, Automatic. With 122k miles.

This is what happens, the CEL will be on, then I will fill the gas tank up and drive it, the CEL light goes off and the engine will run pretty smooth. When the tank gets to about a quarter of a tank, the CEL light comes on and it starts to run a little rough.

I have had it checked and it pulls the code for cylinder misfire 1 and 3, off and on.

I don't have any idea what is wrong with it. I just finally figured out that it is doing it only when it gets to a quarter of a tank of gas.

If you have any ideas I would appreciate the help. I have searched around and got too many hits that didn't pertain to the problem.

Thanks.

from BASIC stoner diagnostics, i would bet it has something to do with your fuel pickup being bent up....
maybe get it down to a 1/4 tank, attach a fuel pressure guage to your fuel rail, and start it... you should see a pretty constant fuel pressure.. if its erratic, either your pump is sucking air, or your pumps going out?

I don't know how the later (after 1996) tanks are made, but the earlier metal tanks with internal fuel pump often had a "dam" around the fuel pick-up and float that keeps the fuel from sloshing around, There are small gaps under the "dam" that lets the fuel level stay even throughout the tank.
Try this. Next time the CEL light comes on, stop the Jeep, get out and rock it back and forth and try to slosh the gas back to the pick-up point. If that works, you've narrowed it down a bit. If the light is still on, the pick-up could be bent up, OR ? ?

Good luck!

I'd guess you've got crap in the bottom of your tank that's making the engine miss, which in turn is triggering your CEL

What year is your vehicle?

2000


here's another shot in the dark:
Fuel pump maybe on it's way out.When your tank starts to get low the pump runs hotter because there isn't alot of gas to keep it cool.....

I tend to go with there might be some crap in the bottom of my tank. It could be a fuel pump on the way out, but it just doesn't make sense why it would be throwing a cylinder misfire code....Maybe I just don't understand it completely.
I will take a look at the FSM when I get home and find out a little bit about the fuel pump.

Thanks.

yep could be either or both!!

2000 take it to Autozone and have them tell you what the codes are next time

I guess i will have to wait a little while. I went to drive the jeep today and light was off, i have about an eighth of a tank left so, we will see if it comes back on. When I drove it last on saturday the light was on and I could tell it was running a little rougher than normal.
I will still check out the fuel pump as a potential problem and crap in the tank.
When I filled the current tank of gas that is currently at 1/8 of a tank, i put fuel additive in it so see if that would improve the problem, chevron techron.