check engine light flashing in 2002 jeep liberty, now black smoke from tail pipe, low mileage, runs rough

sounds like it's running rich. flashing means CAT converter is under duress and may be ruined. It sounds like you have an injector that is stuck on. I would remove each one and run this test on it.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Please run down this guide and report back

Cheers

This car doesn't flash codes.

OBTAINING DTC'S USING IGNITION KEY

Cycle the ignition key ON - OFF - ON - OFF - ON within 5 seconds .
The odometer will show the P-code for the DTC code number. Refer to the DTC chart for a detailed explanation of the DTC codes.
If no DTC's are present, the cluster will display one of two texts: "P1684" and "done" or only "done".

"P1684" is only a status and indicates that the PCM memory has been cleared within the last 50 ignition cycles and does not indicate a problem.
"done" indicates that NO DTCs are present and the procedure is complete.

@Wrenchtech, I did as you requested, display reads "P0306" what does it mean?

That means you have a misfire on cylinder number six (rear one on pass side)and you need to find out why. I woulds check the fuel injector.

Thank you. You don't know how helpful you have been. Do you think I need a tune up, I last had one in Oct, 2010?

Oh BTW is that what caused the "duress" with the CAT converter?

The misfire is what damages the converter. The engine needs to be examined to determine the cause of the problem.

Thank you, the # 6 injector was stuck full on allowing fuel get to enter the engine. I got a new new cost me $78.00 the engine is ruining great thanks for helping me I love this site.

Use 2CarPros anytime, we are here to help. Please tell a friend.

Cheers