Part 1: The First Half Of The Throttle.
Back in early 2011 when I was a relatively inexperienced Cummins ECM programmer I did a 700-rwhp program for an owner operator who had an ISX. He told me a story about his first experience with that program that I’ll never forgot. He transported show horses for a living and the first time he hitched up to his loaded trailer, put the truck in gear, and touched the throttle the truck lurched forward so hard the horses lost their balance and got knocked over.
I learned that there’s nothing difficult about making big power but if it’s not done with care you create a heavy handed brute of a program that is hard on fuel and hard for the driver to control. I see programs every day created by inexperienced programmers that have yet to learn this lesson.
I’ve been on lots and lots of road tests. I’ve even driven a few myself. I’ll sit in the passenger seat if it’s not too cluttered but most of the time I end up sitting on the bed in the sleeper holding onto my laptop. Bobtail my old programs would get me tossed into the back of the sleeper when the driver hit the throttle. This was because I used to program throttles to be more linear and scale throttle position in line with total fuel position. So 10% throttle meant 10% total fuel 20% meant 20% fuel and if the throttle was half way to the floor the ECM would go to 50% total fuel. Factory throttle programming has the throttle as a much more dynamically proportional input device. 10% throttle is usually 3% fuel and 20% throttle is around 8% fuel and half throttle is about 35%. There is good reason for this. The first 50% or so of throttle travel is for running bobtail, cruising, and pulling a light load. If 30% throttle is 90 horsepower and 40% percent is 130 hp hitting a pothole that forces your foot to push the throttle 10% more then you intended isn’t going to cause the truck to lurch forward because that’s only a change of 40 hp. Now imagine 30% percent is 150 hp and 40% is 280 hp. Now that same pothole causes your foot to ask for an additional 130 hp and the truck lurches forward. To make things even worse some newer KWs have throttles with very little travel. Every time I’ve seen one of these throttles I told the owner I’d take it out and install a Williams throttle in its place because I like a lot of throttle travel especially when working with powerful engines. Regardless of horsepower goals the first half of the throttle should be reserved for lower stock like horsepower to maintain drivability and be very predictable. Next month I’ll talk about the second half of the throttle.
Fernando DeMoura, Diesel Control Service LLC.