For those of you who came to our 2021 Victory Road Truck Show, we’d like to thank you. We had 93 trucks and a very healthy spectator turnout. It was nice to have the Pittsburgh Power team together talking trucks and catching up with friends. This year we improved the live dyno runs with two large screen TVs displaying horsepower and torque figures. We also had activities for the whole family, including a petting zoo and balloon twisting. Thanks to Long Haul Custom Detailing, our neighbors across the street, for organizing the event. This will be an ongoing event the first weekend of October every year from now on, so mark your calendar for 2022 now!
Let’s talk about cruising speed. Cruising speed is determined with the gears in the differential, not the transmission. When overdrive was invented, it was considered a “go home empty” gear or “bobtail” gear – diesel engines were not intended to pull loads in overdrive. As the diesel engine gained in horsepower and torque, the manufacturers should have raised the gear ratio, however they stayed with the lower gears such as 4.11, which was the most popular gear in the mid-1970s and 1980s. Even in 1986, when the NTC Twin Turbo 475 Big Cam Cummins was popular, most trucks still had the 4.11 gear ratio.
Back then, tall 24.5 tires were the standard, so the 4.11 gear was about the same as a 3.70 gear using the low pro 22.5 tires we have today. The very first truck we re-geared to run the single overdrive 13-speed transmission in 12th gear direct was a 359 Peterbilt powered by an NTC 475 with twin turbos that we rebuilt to 800 horsepower. We removed the 4.11 gears and installed 3.08 gears, but the owner was concerned that he would lose pulling power. I reassured him that he would gain power on the hills because overdrive lost power. Direct gear is always the best gear to pull a hill or mountain.
This owner operator lived on Martha’s Vineyard, an island south of Cape Cod in the Atlantic Ocean, but the rig stayed in Massachusetts. On his first trip, the owner called me and said he loved how the engine ran and how it pulled in 12th direct gear. Most of today’s 13- and 18-speed transmissions are double overdrive, so 11th is the direct gear in a 13-speed and its 16th in an 18-speed. With today’s automatics, you need to call the manufacturer of the transmission and ask them for the gear ratio splits to determine which gear is 1 to 1, which is direct. The general rule is taking your current gear ratio, subtract the number by 90, and that will put you close to the gear to run the transmission in direct gear. For example, 3.55-90=2.64, 3.36-90=2.47, etc. I know it’s not exactly minus 90, but we can only work with the gear ratios Eaton and Meritor manufacture.
3.08 is a great gear for the X15 Cummins, as 70 mph is 1,360 RPM in double overdrive, so to be in direct gear, you would need a 2.21 (or something close). Unfortunately, Paccar (Kenworth and Peterbilt) will not install a 2.21 gear, saying nobody needs a 120-mph truck. They don’t understand that running in direct gear at highway speeds gives you a .5 mpg improvement, along with a quieter and cooler engine and transmission. Volvo, Mack and Freightliner are building trucks to run in direct gear, so I don’t understand why Paccar is not doing the same. We love their trucks and the Cummins X15, but they need to realize the advantages of pulling in direct gear.
For those of you with a newer emissions truck, here is some technical information regarding inducement strategies. The EPA requires engine manufacturers to enforce an engine derate when there are issues with the EGR or SCR system. While there are derates for the DPF and engine protection, we will be focusing on the SCR system here. Numerous questions around this topic have emerged since the shortage of Urea Quality Sensors. Most people want to know what exactly “SCR Inducement” is and how long they can run with this light on. A message on the dash will appear when the ECM has detected a fault with the system. This message may read differently based on the truck you have. It may read “SCR System Fault Engine Will Derate in 1 hour” or “SCR System Altered or Fault Detected” – if you see a message like this, you could experience an engine derate.
There are multiple levels of engine power derates, known as inducements, that are enforced when a fault condition exists. For a Urea Quality Sensor (UQS) fault, the steps are: warning, torque derate 1, torque derate 2, then severe derate. The first step, warning, will turn on a check engine light and/or a MIL light. Torque derate 1 reduces engine power by 25%, while torque derate 2 reduces engine power by 40%. A fault that has not been addressed will result in a severe derate that will eventually reduce vehicle speed to 5 mph.
The 5-mph limit will not be applied until the ECM finds it safe to restrict vehicle speed. The truck will not immediately reduce speed to 5 mph on the highway, even if the timer threshold has been met. The ECM would need to see an extended idle time, a key cycle, or a fuel refill to apply the 5-mph limit. With an EGR or SCR system fault that is not a UQS or non-circuit error SCR system fault, only torque derate 1 will be enforced. A circuit error such as a disconnected tank sensor, def pump, NOx sensor, tank heater, or dosing valve will result in an SCR system tampering condition. A tampering condition will follow the warning, derate 1, derate 2, and severe derate process.
For a failed UQS sensor, the ECM will impose the following inducement strategy. When the ECM recognizes the issue with the sensor the check engine light will illuminate for one hour with no engine power derate. After one hour, a 25% derate will be applied for four hours, unless the issue is resolved. In that case, engine power will be immediately restored. If the issue is not resolved within 5 hours of the check engine light coming on, a 40% power derate will be ramped in until the ECM determines it is safe to limit the truck to 5 mph. At this stage, if the fault goes inactive, the ECM will be “sensitive” to SCR faults. For the next 40 hours, after vehicle speed has been restored, any SCR tampering fault will send the truck immediately back to a 25% derate and starts the cycle over again. However, after 40 hours of no active faults, the timer will be reset, and all will be good.
For Cummins engines, there is now a software update that will allow the truck to run at full power with a damaged UQS sensor. The UQS sensor is a 3-in-1 sensor that is comprised of a urea temperature, level, and quality sensor. You can get this calibration at any Cummins dealer or at any of our remote tuning locations. Call (724) 360-4080 or visit www.pittsburghpower.com to find a location in your area, or stop by our shop in Saxonburg, PA. We are always here to help!
