So my 4.2 has run amazingly well for the year that I've had the Jeep so far until a few weeks ago and I can't figure out what's wrong.
The problem is that most times it just doesn't run smoothly anymore... when the engine is cold or I've just driven on the highway for more than 5 minutes, it idles like it's running on 5 cylinders (whole Jeep shakes). And then when I go to accelerate, it's rough until it gets above 1500 RPMs.
It's weird, in city stop-and-go traffic, it seems to run as smoothly as ever. But if I cruise at any speed, especially at say 40 MPH or more, for more than a couple minutes it will run real rough between idle and 1500 RPM afterwards, until I do more stop-and-go.
I messed with the carb mixture and regapped the plugs which seemed to help a little, but its still not gone. I don't know what else to do!!
It really seems like one cylinder won't fire sometimes, but I'm not sure why, or what to do about it. I really need this thing tip-top before I make the drive back to school in a couple weeks, so PLEASE HELP!!
'87 YJ Laredo
- 4.0L, AX-15, NP231, 4.10s: 3.5" BDS, 31" Muds
- Donated drive train to the YJ, Parted out the rest
- Buick 225 V6: Painless Wiring Harness, Warn Overdrive & Hubs, 2" Lift, 31" Muds