2 DTC Codes - related?

All:

Got these to ODBII Codes on Saturday...

P0302 Cylinder 2 Misfire Detected

P1494 (M)
Leak Detection Pump Sw or Mechanical Fault

Started Misfiring next day.

2000. 4.0. New Plugs 3 months ago. 147K. Only change recently was putting on a Dynomax Catback. Replaced Gas Cap hoping to correct Leak Detection error code - no luck. Any thoughts?

Z

:us:

"Dynomax Catback" the plastic vacuum vent runs close to the cat, did you melt it?

Checked it out. All is fine underneath...

The first code is a misfire. It takes several detected misfires to trigger the error code, so something is definitely wrong there. Pull all the plugs and have a look just to be sure. Could also be a problem with the coil rail, valvetrain, etc. This requires more diagnostic time.

The second code is probably a bad leak detection pump. Check all the wires around it (I don't know offhand where they are on Cherokees), might be a good idea to get a FSM and go through the diagnostic procedure to be sure it's a pump problem and not a wiring problem, but it's probably the pump. 99.9% of the time a new gas cap will NOT fix an EVAP code.