Jeep Coil Pack being cooked?

On my 2000 Jeep Cherokee 4.0 liter 6 cylinder, my vehicle was spewing black smoke out of the back when under power, and all except one of the cylinders were suffering from random misses. Also, the car was sluggish.

I just replaced the coil pack (this model is all electronic; no distributor or plug wires), and the car ran beautifully… It was powerful, the black smoke only happened once and never again, the engine light turned itself off, and the vibration it had was gone. That only lasted 20 miles or so.

When I was about to pull over and declare victory, the car started losing power rapidly, was vibrating horribly, and the engine light started flashing (though, still no black smoke thank god). I let it sit and cool down, then I removed the coil pack and cleaned it again (it was used when I bought it), I pulled my spark plugs (the first is in good shape, the others had dry black deposits on the electrodes) and replaced them.

Here is my question: Considering how beautifully it ran for 20 miles before crapping out, could something be causing damage to my coil pack?

The coil problem is more than likely a symptom, not the cause, of your vehicle’s problems.

Maybe you have a failing fuel pressure regulator. A failing regulator allows raw fuel into the intake which causes an excessively rich fuel/air ratio which kills the spark plugs which can kill a coil if it continues.

Disconnect the vacuum line from the fuel pressure regulator and see if there’s gas in it. If so, the FP reg. diaphragm has ruptured.

The engine is running very rich. You need a mechanic to check those things which can cause this: Fuel pressure regulator; engine coolant temperature sensor; intake air temperature sensor; MAP or MAF sensor; front oxygen sensors; idle air control valve. One can do these checks with a multimeter and the repair manual.