On my way home, minding my own business, and suddenly my 97 4.0 beast starts misfiring, badly enough I thought I had just run out of gas. Checked the gauge - half full.

Got it home and checked for codes. P300 (random misfires), 301, 303, and 304. That's cylinders 1,3, and 4 misfiring.

Checked the cap and rotor - pretty nasty. Carboned up pretty badly. I cleaned it up and put it back together to get to work tomorrow.

I don't know for sure when I changed it last - I lost my records in a phone swap. Anyway, I think it's been about 2 years, and it's at least one year. Whenever it was, I did the plugs, rotor, cap, and wires at that time.

I'll pick up new tomorrow, but here's the question:

Why so suddenly?

It hasn't been running great, but this was like flipping a switch. I really thought I'd run out of gas. I've never had that happen before.

 

When you get around to replacing the cap, rotor, wires and plugs, check to see if there excessive up and down movement on the rotor shaft. And see if there's excessive rotary motion in the rotor shaft.


Edit: The Camshaft Position Sensor is probably ate up as well. Replace it.

 

Ah, good thought!


What would be excessive? Any?

 

I think up and down and rotary should not exceed 1/8" (at least that's abut the play I have in mine.


If you search around there is a relatively current post about excessive play in the distributor shaft.


Edit: Here - https://www.cherokeeforum.com/f2/cou...p-code-211337/

 

Well, no problem with the play. A new coil, rotor, cap, wires, and plugs from NAPA and it's purring like a kitten.

Still puzzled by the suddenness of the misfire. Maybe the resistance of the cap/rotor just got to the point where a weak coil couldn't overcome it anymore.

 

 

Well, the mystery deepens. Back to running badly, again, like flipping a switch. Rather than have two threads going, I'll link to my newer one, for any who are trying to chase down similar problems.

 

Deleting message from this thread as it did not belong here.