tprman Posted September 4, 2014 Share Posted September 4, 2014 I need a little help. I have a 1990 MJ 4.0. It started running ruff and black smoke coming out the exhaust pipe. It back fires and it sounds like it's skipping while idling. I tune it up and change the fuel filter but that didn't help. Any ideals. This MJ has been setting for 2 years. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 4, 2014 Share Posted September 4, 2014 Check the tube from the throttle body to MAP sensor on the firewall. It must be perfect or your MJ will run pig-rich. Link to comment Share on other sites More sharing options...
tprman Posted September 5, 2014 Author Share Posted September 5, 2014 I noticed that line was not hooked up in the back of my throttle. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 5, 2014 Share Posted September 5, 2014 And? Click on my Tech Photos link and you'll find some diagrams/photos of that hose. Link to comment Share on other sites More sharing options...
Eagle Posted September 5, 2014 Share Posted September 5, 2014 How old is your oxygen sensor? Blue smoke means burning oil. Black smoke is carbon, and the usual cause of black smoke is a very rich mixture -- which can be the result of a dying oxygen sensor. Link to comment Share on other sites More sharing options...
metrictonner Posted September 6, 2014 Share Posted September 6, 2014 I got this problem when I was trying out MAT replacements. I thought I had lunched my engine. Link to comment Share on other sites More sharing options...
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