Still trying to figure out this issue with my jeep. recently ran a diagnostic and three codes popped up. Large evap leak, lean fuel, and no mic/bus. i know what the no mic/bus is. it's the gauge cluster easy enough fix but the least of my worries. runs rich because black sut comes out of the tail pipe at start up and when I gas it. Horrible gas mileage. I am doing the smoke test next week. but the thing that throws me off is the lean fuel code. why would it do that if it's running so rich? Also idles really low almost misses but not hard enough to through a check engine light. OH here's the kicker. While all this is going on, the check engine light does not come on. I had to run a diagnostic machine (snap on solus) to figure it out.

 

large vacuum leak is leaning out the mixture causing the ecm to dump extra fuel in causing bad gas mileage

 

What about the no check engine light?

 

some systems will not show a light for a soft code these are smalll issues that arrise major codes or hard codes will throw a light

 

Thanks I'll work on the evap leak and hopefully that solves all my problems