Hello, I have a 1996 K3500 6.5 liter diesel w/157k miles. I was driving with the cruise control set at approx. 70 mph. I was not pulling or hauling anything. When i would start up just a slight incline, black smoke would start coming out the exhaust. as soon as the pull was over the smoke would stop. I replaced the fuel filter a month ago along with the air filter. what could be causing this?
What type fuel additive should I be using??
Any suggestions would be helpful.:grd:

Most likely turbo problems. Lack of boost with lots of fuel will cause lots of black smoke on high load. Check the turbo wastegate function. If the vacuum system that runs the wastegate has a problem, the wastegate will stay open, and you'll have little or no boost and plenty of black smoke.

Howdy Lewis,

Welcome to the site

WG is most probable suspect as 454 suggests, go through the vacuum system make sure it is there then look for electrical problems for WG sol command.

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