Mack MP7, MP8 & MP10 Running Rough / Misfire


Several things could be causing rough running or a misfire in your Mack Semi:

Problem: Stiction

Problem: Mechanically failing injector(s)


A condition of running rough can be one of many factors. If the truck runs rough when it’s cold but clears up when the engine is warm, you have a stiction issue in your injectors. Treating with Diesel Extreme will clear out the debris in your injectors.
If the truck runs roughly only at idle, a stiction issue is likely, so treat this the same way.

If the truck is running rough all of the time, it can be a little more complicated. An injector may have gotten beyond the point of our product cleaning it. An injection pump may be failing, or a pump may have gotten out of time.

An electrical issue, such as sensor failure, can affect your truck in a similar way. You will need a scan tool to properly diagnose this.

The hardest to diagnose is an intermittent miss. It may be best to take the vehicle to a professional, depending on how good you are with your vehicles electrical system.

If you have any questions, feel free to contact one of our diesel experts.

The contents of, such as text, graphics, images, and other material contained on the Diagnose Your Diesel section are for informational purposes only. Always seek the advice of your mechanic or other qualified professional with any questions you may have regarding your vehicle’s condition.