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

​DDEC Timing shifts

By Fernando DeMoura

April, 2016

There are tens of thousands of parameters in an ECM program but at the end of the day those calculations boil down to two basic things, injection timing and pulse width. In other words, how much fuel to fire and when to fire it? I’ve been tuning ECMs since around 2008 and for most of that time I knew a job was a success because the truck would put down more power to the road or a dynamometer. The basic idea was increasing engine output by increasing fuel quantity. At light and medium loads timing was almost always left alone because even with access to a dynamometer DDEC timing shifts were difficult to predict and control. It wasn’t until I constructed the ECM lab and electronically controlled every variable that I realized the true nature of these timing shifts. 

This all started by accident in March when I was running a 98 DDECIV 12.7 model TK for a customer. I took his DDEC IV to 1200 rpm and started charting out the injection timing and pulse width of his stock 500 program at 20 percent throttle. I worked my way up to 100 percent then I brought it back down to 20 percent. When I compared my numbers I thought I had done something wrong. The timing was completely different. After a while I realized that after being held at 1200 rpm for more than 26 seconds the timing would shift from 3 degrees BTDC to 24 degrees BTDC. No temperature or pressure changed, no change in throttle position, no change in rpm, only the fact that nothing changed for 26 seconds triggered the shift. I figured what I was seeing was either an old TK defeat device or an error in the programming. As it turns out TK programs have been mostly wiped out by dealer reflashes and what I was seeing was a defeat device. A program that was original from the factory from 1998. Since that first test I have also found that memory errors in an ECM program can also cause a timing shift to happen randomly, mostly in a way that makes the truck run and smoke worse.

So why do timing shifts matter? Injection timing determines how much heat your engine absorbs and how much heat ends up in the exhaust. A shift in timing can be heard and can make your water temperature rise and your exhaust gas temperature drop. Proper injection timing makes the difference between an ECM program that gets good mileage and one that gets bad mileage. So if you believe your engine has good days and bad days and sometimes it just sounds different…you might not crazy. It may be a problem with your ECM programming.

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