My wife's Cherokee is running badly.........well....sometimes. That's the pain of it. It doesn't do it all of the time. It doesn't seem to have anything to do with the temperature of the engine either. I have checked several forums and have come to the conclusion that first, I should check the pressure at the fuel rail. If that checks to be o.k. and it's not the fuel pump I plan to start changing out sensors. Can someone tell me where to start in this process, or, perhaps, give me insight as to how to fix this? It has a 4.0 in-line six cy. Auto trans.
I am not a mechanic, but I'm not afraid to attempt the work, except the CPS. I hear it's a real pain in the .........

Thanks for any and all help. tommy

How many miles? How long since last tune up (plugs, cap, rotor)?

When you say running badly, can you describe more fully? Does the engine run rough, sputter, or cut out entirely?

CPS isn't too tough, just a hard reach/fit for your hands. There are numerous threads about it

Thanks, Fred, for your quick response.

She has about 135,000 miles on her. We changed the plugs about six months ago, but not the cap or rotor.

The miss we are experiencing is not consistant. Sometimes it's like only 5 cylinders are firing, sometimes it is just a little sputter, sometimes it runs like new. We have not experienced a complete stall yet, but it seems like the miss is happening more often than before. The check engine code procedure only gives us a 55.

I'd definitely throw a cap and rotor, and check the condition of the plug wires.

But your occasional miss sounds a lot like the crankshaft position sensor.

Here's a thread about replacing the CPS: Click me (http://www.automotiveforums.com/vbulletin/showthread.php?t=579517)

I mean it could be fuel delivery or another electrical part, but the CPS definitely does go out eventually....

Thanks,

I'll do the cap and rotor thing first and then move on to the CPS. I'll let y'all know if it works. Thanks again.