you may have broken the 02 sensor, which controls fuel trim. this would explain rich condition, black smoke, and poor mpg. what year is your truck. the pre-cat 02 sensor is the one(s) thats important. (california has 2). post cat 02 is not important unless its specifically throwing a code. all it does is monitor the cat and does not control fuel mix.

 

X2. Definitely sounds like your front O2 sensor has gone out. When the O2 sensor goes out, the ECU doesn't know how much fuel to dump in, so it opens the floodgates on the injectors and pours the gas into the cylinders. Black smoke always (ok, so almost always) equals rich as hell.

 

Assuming you did the vac check correctly ,(which is how I do it per my OTC Genisys troubleshoot) You have a bad Plenum! Simple as that. You can also do a search for the Chrysler TSB and do it that way , slightly different but same result.

 

And BTW ! If it is done correctly you are bypassing any other vaccum controlled systems. And I would also say that it is entirely possible that more than one problem exists ,like the ones others are suggesting.

 

well I will probably check everything you people are recommending with a dvom considering I don't want to put anymore money into this thing than I have to. Zman, are you certain that's a good way to check the plenum gasket. I was thinking that was the problem when I first started having the rough idle and smoke.

 

Of course I'm certain! But you have to go through the most common and least expensive ways to troubleshoot your problem.

 

I meant to say, Of course I'm NOT certain. LOL! Yes I'm certain that is a good way to check the plenum. And NO, I'm not certain that it;s your only prob.

 

Zman, all i needed to know was if that was a for sure way to check the plenum. Thanks a lot for the info, as i am almost 100% sure it is the plenum as well. It happened right after i seafoamed it which i am sure while it was sitting down there it made the plenum leak by eating all the carbon off the leak that was already there. The before cat 02 sensor is just fine, there are no codes for it and it checked out when i tested it. After i get back from vacation and can spare the money i am going to throw a plenum gasket on there and hope that it fixes the problem.

 

Grab a can of carb or brake cleaner and start spraying around the base of the plenum and any suspect vacuum lines or components. If the idle changes noticeably, you've found your culprit.