GMC Repair: 1999 GMC Jimmy, fuel pressure regulator, gmc jimmy

Question
I have had my truck (a 1999 Gmc Jimmy) to the gargae 4 times and the mechanic can't figure out whats wrong. It has had misfires, is blowing black smoke. It smells like rotten eggs and is spitting and spoutering. They have replaced the dist. cap, spark plugs, fuel pressure regulator. Any ideas? We are despreate but tired of sinking money into it with no results.  

Answer
There are so many possibilities and tests that need to be performed using special equipment that an accurate diagnosis or specific test procedure to make a diagnosis is most impossible.

could be a coolant sensor problem and or a internal computer fault.


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