Ford Repair: 91 Ford Ranger, blown head gaskets, mass air flow sensor

Question
Followup To
Question -
Hey, I was wondering if you could tell me whats wrong with my ford ranger. My check engine light is on, I know theres a misfire, my fuel mixture is running too rich, it idles rough (like the rpms will bounce back and forth like a wave, from 700 to 900, when in idle), there is a bad valve tap (valve tap or my headers, or something), and my gas mileage is at like 10 mpg, and my oil turns smoke black within weeks of a new oil change and its not from the old oil. I replaced the O2 senor, and put in new spark plug wires and spark plugs, and it still runs like that. Could you tell me whats up?

Answer -
what engine does it have?

Glen-
It has a v6 4.0

Answer
Hello and thanks for the reply...I'll try to help.
 I would suggest that you find out why your check engine light is on. Either by bringing it to a repair garage or renting a scan tool.
 It seems to me that you might have a MAF(mass air flow) sensor that has gone bad, or another fuel related problem.
 Another possibilty could be the trigger wheel on the crank shaft being damaged or the crank shaft sensor being bad.
 You really need the fault codes read.
 Another thing, have you checked the coolant level? If it's low, find the leak. The 4.0L has been known for having blown head gaskets, and or cracked heads.
Hope this helps,
Erik