Proudly Serving The American Truck Driver Since 1975     Contact    Advertise    Digital Print    Archives

​How The Wrong Injector Trim Codes Can Damage A Cylinder

By Fernando DeMoura

July, 2019

Those of you who’ve read my old articles know I’ve written about injector trims before but the short of it is this. When a 1994-2006 Detroit injector is flow tested a 2-digit trim code is stamped on the injector. This code needs set in the ECM so the computer can compensate for how far above or below spec the injector flow rate is. We want each cylinder to get the same amount of fuel. When the trims are all set to the same number some cylinders are going to get more fuel, run hotter and see more pressure than the others. The hottest cylinder becomes a weak link and here is the worst part…the coolant, oil, and pyro temp are all reading the combined heat from all 6 cylinders so those values can only be looked at as the averages of all 6. 

why am I bringing up this old subject? Well…about two weeks ago I finished repairing and programing a DDEC IV for an owner operator we’ll call Johnny. Johnny had an early BK60 and this engine is known to be a strong and capable 12.7 Series 60. A few days ago, Johnny called me back. Although I’m used to getting feedback about successful repairs, good power and better mileage that doesn’t mean I don’t enjoy hearing about it but that’s not what happened this time. Johnny asked me how much I would charge him to restore his old 430hp program. “I wouldn’t charge you anything besides the return shipping. What happened?” Johnny replied: “I was pulling a hill and I smelled something burning. Checked my oil and it was low. Drove a little more and my oil got lower. Got it into a shop and they said I lost the #4 cylinder. I never got it hot”. While I was listening to Johnny’s story, I was looking through my notes on Johnny’s original program. I pulled up the injector trim codes that were in the ECM when I first checked it in. All six injectors were set to 07. That’s a problem and when I see all the same injector trim from cylinder 1 to 6, I call or text the owner and let him know. If we know the real trims, I put them in otherwise I set the injector trim password to 0000 and tell them to update the trims when they can. Unfortunately, in the two weeks Johnny had been running he was unable to get his trims updated. 

I’d say about 1 in 5 DDECs I see have “01” or “75” set for all the injector trims. Some techs set all the injector trims the same when they don’t know the trim values and are too lazy to pull the valve cover and look. Other times they don’t realize the trims need set when a blank ECM gets flashed or when the injectors are changed. 

Trim code 75 is what most of these parking lot programmers are using to get a little more power out of a Series 60 engine. A few mouse clicks and a few dozen keystrokes and the engine makes on average about 8 percent more power at full load than it would if the trims were set at 01. I ran some tests on the bench last night and found that trim code 01 and 00 are NOT the lowest trim code flow values. The trim number values don’t follow a pattern and don’t scale. For example, 12 gives more fuel then 75 and 25 gives less fuel than 01. Trim code 07 is one of the stronger trims and if Johnny’s #4 injector has a higher flow rate the #4 cylinder could have been getting as much as 22 percent more fuel than the other cylinders. Johnny’s water, oil, and pyro temps never got hot and in this case they wouldn’t because when the #4 cylinder works that much harder the other cylinders can back off and don’t generate as much heat.  

If you send in your DDEC for service I will not change your trim codes unless you tell me to. If your trims are wrong and you send that information along with your DDEC I’ll gladly update them no charge. If you’re not sure send the correct trim codes anyways and I’ll check them. 

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