1984 GMC2500 6.2 diesel light blue smoke
 

I have a 1984 GMC 6.2 diesel
when i hit bout 50mph to 65mph light blue smoke is pooring out the passanger tail pipe and i know its running rich cuz i can smell it and it acts like it has no power and it spits and spudders and i would like to know if anyone has any idea on what could be the cause of this and iv owned this truck for about 4 weeks and this is the first time it has done this and on another note this is the frist diesel i have ever owned and its been a great truck any ideas on what this could be would be really helpful

What could be the cause of this and iv owned this truck for about 4 weeks and this is the first time it has done this and on another note this is the frist diesel i have ever owned.

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