High Performance Diesel Engines

Bruce Mallinson, Andrew Wilson, & Leroy Pershing
November 2021

For those of you who came to our 2021 Victory Road Truck show, we’d like to thank you. We had 93 trucks this year and a very healthy spectator turnout. It was nice to have the Pittsburgh Power team together talking trucks and catching up with old 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. We would like to thank Long Haul Custom Detailing, our neighbors across the street, for organizing the event this year. If you missed it, this will be an ongoing event the first weekend of October every year from now on. So, mark your calendar now for next year!

CRUISING SPEED should be determined with the gears in the differential, NOT the transmission.  When overdrive was invented, it was considered a go home empty gear or a bobtail gear, diesel engines were NOT intended to pull a loaded trailer 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 during the mid-1970’s and 1980’s.  Even in 1986 when the NTC Twin Turbo 475 Big Cam Cummins engine was popular, most of the trucks had the 4.11 gear ratio.  Tall 24.5 tires were the standard, so the 4.11 gear was about the same as a 3.70 gear using a low pro 22.5 tire that 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 twin turbo that we rebuilt to 800 horsepower.  We removed 4.11 gears and installed 3.08 gears; the owner operator 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 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, however, the Peterbilt stayed in Massachusetts.  His first trip he 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 a double overdrive, so the direct gear in a 13 speed is 11th gear, and 16th gear in an 18-speed manual transmission.  With today's automatics you need to call the manufacturer of the transmission and ask them for the gear ratio splits so you can 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.  Example: 3.55- 90 = 2.64, 3.36 – 90 = 2.47 gear.   Yes, I know it’s not exactly 90 minus, however, we can only work with the gear ratios Eaton and Meritor manufactures.  3.08 is a great gear for the new X-15 Cummins, 70 miles per hour is 1360 RPM in double overdrive, so to be in direct gear you would need a 2.21 or something close to that.  The trouble is Paccar, Kenworth and Peterbilt will not install a 2.21 gear, they say you don’t need a 120 miles per hour truck, they just don’t understand that running in direct gear at highway speeds is about ½ mile per gallon improvement in fuel mileage, the engine runs quieter and cooler, the transmission is also quieter and cooler.   Volvo, Mack, Freightliner are building trucks to run in direct gear, I don’t understand why the Peterbilt, and Kenworth engineers are not doing the same.  We love their trucks, love the Cummins X-15 engine, but they need to realize the advantages of pulling in direct gear.

For those of you with a new emissions truck, here is some technical information regarding inducement strategies by one of our engineers, Leroy.  The EPA requires engine manufactures 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 in this article. Numerous questions around this topic have emerged since the shortage of Urea Quality Sensors. The main question is: What is an SCR Inducement and how long can I 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 your dash reads something 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 fault, the steps are: warning, torque derate 1, torque derate 2 and 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 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 5mph 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. When a 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, dosing valve will result in an SCR system tampering condition. A tampering condition will follow the warning, torque derate 1, torque derate 2 and severe derate process.

For a failed urea level/temperature/quality 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 5 hours after the check engine light illuminates 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 in-active 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% that starts the cycle over again. However, after 40 hours of no active faults the timer will reset, and a severe inducement will not be applied until 5 hours of an active tampering fault.

For Cummins engines there is now a software update that will allow the truck to run at full power with a damaged UQS sensor. A UQS sensor is a 3 in 1 sensor, that was mentioned previously, that comprises a urea temperature, level, and quality sensor. You can receive this calibration at any Cummins dealer or at any of our remote tuning locations. Visit pittsburghpower.com to find a location in your area. 

Written by; Bruce Mallinson, Andrew Wilson, & Leroy Pershing; Pittsburgh Power Inc.; 3600 S. Noah Dr., Saxonburg, Pa. 16056  Website: PittsburghPower.com. Phone 724-360-4080