Having Misfire

i recently swapped out the 4.0l for another 4.0l with less miles after the swap i put new plugs, wires, cap, and rotor in started just fine and ran just fine.....

i later that week took it in the woods and started to get a misfire...on the drive home a check engine light came up.....the misfire only seemed to occur at low RPMs and take off....once i hit about 3500RPMs it seem to fire just fine......

do the XJs 4.0 motor require any special kinda of plugs the ones i put in were copper....im thinkin it might be the plugs cuz i checked the cap and cleaned it out for water and nothing...... any idea wut this problem could be.....

The 4.0L is happiest with plain Champion or NGK plugs.

MJR said:

The 4.0L is happiest with plain Champion or NGK plugs.

Click to expand...

Do you think the plugs are the reason i might be having a misfire

MJR said:

The 4.0L is happiest with plain Champion or NGK plugs.

Click to expand...

my '99 loves Bosch plugs

tomcat said:

my '99 loves Bosch plugs

Click to expand...

are they copper plugs, iridium plugs or what

I have the Bosch Platinum +2 plugs in mine, they were installed in the general tune-up done by the dealer I bought the Jeep from before I took ownership. Seem to work fine, I get good gas mileage. I'll probably change them to regular copper plugs at some point in the future just to see if there is anything I'm missing out on. My jeep does dog a bit when accelerating in the lower RPM range, maybe it's the plugs, maybe it's normal or maybe there is something else wrong?

ColoradoRaptor said:

The likely hood of the plugs being the culprit is slim!! I would check to see if the wires are secure, then make sure the distributor is tight! If that is not it then I would check all sensors. This is where I would start!

Click to expand...

i checked the wires they are all on secure to the plugs and to the cap....i do have a check engine light on so ill hook up a sensor and see wut comes back....im thinking its an O2 sensor

Check the sensor wire connections, especially the O2 sensor connection as it is a low lying target for brush to grab onto. The TPS hates water, it has ruined many a good TPS from what I have heard, did you get the TPS wet or any of the sensor connections?

Check and post that CEL code!