How to Adjust a Cummins Fuel Pump

by Francis Walsh

Dodge diesel engines are well known for having outrageous torque available upon the press of the pedal. Adjust a Cummins fuel pump to get more power right from the factory. Blowing black smoke out of the tailpipe is a good thing when a Cummins engine is tuned correctly at the fuel pump. Some owners adjust a Cummins fuel pump to handle fuel requests made by after-market parts, but even more do it as an easy way to get more power from a Cummins diesel engine at no extra cost.

Locate the Cummins fuel pump located near the firewall of the cabin on the passenger side of the engine. Wipe the top of the pump and the back of the housing to remove grime and dirt from the surface.

Loosen the smoke adjustment nut on top of the fuel pump to remove the cap over the fuel load delivery plunger and spring. The plunger is offset on one side at the bottom. The plunger can be turned when the cap is removed.

Turn the plunger 180 degrees so that the opposite side of the offset plunger is now the surface the fuel delivery pin rides up and down to adjust fuel delivery. Secure the cap back over the fuel delivery plunger and tighten the smoke adjustment screw to hold the cap in place.

Remove the metal collar at the base of the fuel adjustment bolt. Underneath the diaphragm holding the fuel delivery plunger there is a power adjustment screw locked in position by a lock nut. Use a wrench to loosen the lock nut enough to unscrew the bolt from its position. When the bolt is retracted out far enough to remove the metal collar around the base of the bolt, remove the metal collar. Screw the power adjustment bolt back into position, turning the bolt one extra turn before locking it in place with the lock nut.

Test the performance of the fuel delivery adjustments you made. Adjust the Cummins fuel pump to reduce the amount of smoke at idle, and adjust the depth of the power adjustment bolt until the setting works in combination with the new position of the fuel delivery plunger. Loosening and tightening the adjustable bolts of the smoke adjustment tool and the power adjustment bolt will tune the new fuel being delivered to the engine via the fuel delivery plunger and the accelerator pedal.


  • check Mark the factory positions of every part you will be adjusting before making the adjustment. The position of the fuel delivery plunger, the smoke adjustment screw, and the power adjustment bolt should be marked on the fuel pump housing before adjustments are made to keep track of how the pieces are moved in relation to their starting position.

Items you will need

About the Author

Francis Walsh has been working as a freelance writer since 2003. He has contributed to websites such as Shave, Autogeek and Torque & Chromeas, as well as provided content for private clients. Walsh has worked as a performance part-packer and classic car show promoter, now serving as crew chief for Nitrousfitz Racing.

More Articles

Photo Credits

  • photo_camera Tankstelle image by Ewe Degiampietro from