I have a 1999 5.9 with 94000 miles. Sometimes it has full power then it will get weak for a while. I took the chip off and changed the filter and no change. It use to show extra fuel in smoke but not now. Pump is two years old surely not again. What is it?????

 

If you have no trouble codes and are experiencing erratic power problems it is most likely the VP44 injection pump. But, before you panic do a complete scan for trouble codes.

Trouble codes will help you identify where to do additional diagnostics. No trouble codes and it is just about a guarantee that it is the injection pump.

If it is an automatic, it could be as simple as a failing throttle position sensor, but there will be one or more codes to point you in the right direction.