Hi, I'm a newbee to this board. I have a 1993 4.0 automatic with 150k that has a constant ticking sound during and after warm up and at all times sounds like a diesel motor (I had a guy say to me "I didn't know they made a diesel wrangler" I replied "They don't"). Smoke comes out of the tailpipe under hard throttle. I don't know the color yet, but it smells like it has too much fuel in the mixture. I recently changed all the spark plugs and found that there were signs that they all had been used way past their service life. Also, during recent fill ups I did the math and found that 13.5 mpg is the average (my gas gauge doesn't work). Any help would be great.