​Injector Trim Codes: What They’re For And How They’re Abused

Fernando DeMoura
January 2017

First let’s look at what trim code is and how they help your engine run smoother.

When an injector is built, or rebuilt it’s flow tested. Depending on the result of the flow test the injector is given a trim number. That code represents the flow characteristics of that injector. The purpose of trim codes are to compensate for the differences in fuel flow between all six cylinders and once they are properly set in the ECM the low flowing injectors stay on for longer and the high flowing injectors stay on for shorter. When the injector trims are correct is each cylinder gets the same amount of fuel.

When all these numbers are set to the max value the ecm no longer compensates for the mechanical differences between the injectors so some cylinders are getting more fuel and some are getting less. Some cylinders work harder and run hotter and some cylinders run colder. When you push the engine hard your temperature gauges are showing you average temperatures between all six cylinders. If your trim codes are all set the same we know some cylinders are working harder and burning hotter than others but we don’t know how much hotter when we can only see combined EGTs and water temps from all six cylinders. The way I look at it…why make a weak link if you don’t have to?

The two-digit number you see in the photo indicates the injector trim number. These should be programmed into the ECM any time an injector is replaced.

Written by Fernando DeMoura, Diesel Control Service LLC. www.dieselcontrolservice.com Phone 412-327-9400.