DDEC VI Driving Tips

Accelerating the Vehicle

The accelerator pedal was designed to communicate “percentage” of accelerator pedal travel to the engine MCM. A throttle characteristic you may need time to get used to, is the DDEC limiting speed governor. This allows the driver to command total engine response between idle and rated speed, such as accelerating at half throttle—an advantage when driving under slippery conditions. To obtain 100 percent fueling at any speed, the accelerator pedal must be depressed to the fully pressed position.

Shifting

Depending on your transmission model, the gear split may vary from 400 to 500 rpm. The electronic governor provides almost no overrun capability; if the transmission is downshifted too early, you will experience a temporary loss of pulling power until the engine speed falls below rated speed. In general, when using a 9-speed transmission, you should always downshift between 1000 and 1100 rpm. This is true even on steep grades with heavy loads. When using an 18-, 15-, or 13-speed transmission, you will need to downshift at an rpm that allows “less than rated” rpm, before throttle application in the next gear down. You may want to limit engine speed to 1900 rpm in all gears.

The DD15 engine provides horsepower through 2100 rpm, but fuel economy is not as efficient above 1800 rpm. If you decide to drive at lower rpm for improved fuel economy, don't let different engine noises throw you off guard. The DD15 engine sounds quiet at 1400 rpm, almost as if it had quit pulling. If you had a boost gauge to look at while driving, you would notice the turbocharger maintaining steady intake manifold pressure, even as rpm falls. Depending on the air intake arrangement, you may also hear a “chuffing” sound as the engine starts to pull hard at lower rpm. This is normal, and caused by the velocity changes of the air flow within the air intake plumbing. Electronic engines can actually deliver more fuel at lower engine speeds than at rated speed.

The DD15 engine has been designed for a very quiet operation, but the air flow may be noticeable to the tuned attentive ear. The turbocharger operates at higher boost pressure, forcing exhaust to flow through the exhaust gas recirculation plumbing. In some situations the driver may believe they have experienced a charge air cooler system leak. Even while connecting trailer lights and air hoses, the driver may hear a different tone (exhaust and under hood with the engine idling). If equipped with a turbo boost gauge, the driver may occasionally note the intake manifold pressure exceeds 35 psi (241 kPa).

Idling

The common belief that idling a diesel engine causes no engine damage is wrong. Idling produces sulfuric acid, that is absorbed by the lubricating oil, and eats into bearings, rings, valve stems, and engine surfaces. If you must idle the engine for cab heat or cooling, the high idle function of the cruise control switches should be used. An idle speed of 900 rpm should be enough to provide cab heat in above freezing ambient temperatures.

Cold-Weather Operation

Precautions must be taken during cold weather to protect your engine. Special cold-weather handling is required for fuel, engine oil, coolant, and batteries. The engine does not require starting aids down to 50°F (10°C). A grid heater is included for temperatures between 50°F (10°C) and –4°F (–20°C). Temperatures below –4°F (–20°C), will require a grid heater, block heater, and oil pan heater.

A winterfront may be used to improve cab heating. At least 25 percent of the grill opening should remain open in sectioned stripes that run perpendicular to the charge air cooler tube flow direction. This assures even cooling across each tube, and reduces header-to-tube stress and possible failure. Winterfronts should only be used when the ambient temperature remains below 10°F (–12°C).

Driving on Flat, Dry Pavement

Use the following guidelines when driving on flat, dry pavement.

• If driving on flat, dry, open stretches, with a light load, place the progressive braking switch in the LOW position.

• If you find you are still using the service brakes, move the switch to a higher position until you do not need to use the service brakes to slow the vehicle.

• If you are carrying a heavier load and road traction is good, move the progressive braking switch to the HIGH position.

• Check your progressive braking switch often for proper position, since road conditions can change quickly. Never skip a step when operating the progressive braking switch. Always go from OFF to LOW, and then to a higher position.

Descending a Long, Steep Grade

An explanation of “control speed” may be helpful in understanding how to use the engine brake system while descending a grade. Control speed is the constant speed at which the forces pushing the vehicle forward on a grade, are equal to the forces holding it back, without using the vehicle service brakes. In other words, this is the speed the vehicle will maintain without using the service brakes or throttle.

Use the following guidelines when descending a long, steep grade.

• Before beginning the descent, determine if your engine brake system is operating properly, by lifting your foot briefly off the accelerator pedal. You should feel the system activate.

• Ensure the progressive braking switch is in the appropriate power position. Check your progressive braking switch often for proper position, since road conditions can change quickly. Never skip a step when operating the progressive braking switch. Always go from OFF to LOW and then to a higher position when on slippery roads.

• Do not exceed the safe control speed of your vehicle. Example: You could descend a 6 percent grade, under control at 10 mph (16 km/h) without an engine brake, but at 25 mph (40 km/h) it requires an engine brake. You could not descend that same hill at 50 mph (80 km/h) and still expect to remain under control. Know how much slowing power your engine brake can provide before descending hills, and do not exceed a safe control speed.

Driving on Wet or Slippery Pavement

On wet or slippery pavement, start with the main switch in the OFF position and use the gear you would normally use under these conditions. If the vehicle is maintaining traction, place the selective braking switch in the LOW position and turn ON the engine brake system. If the drive wheels are maintaining traction and you desire greater slowing power, move the braking switch to the next higher position. However, if the tractor drive-wheels begin to lock, or there is a fishtail motion, turn the engine brake system OFF immediately and do not activate it until road conditions improve.

Check your progressive engine braking switch often for proper position, since road conditions can change quickly. Never skip a step when operating the progressive braking system. Always go from OFF to LOW and then to a higher position. See General Information for the proper operation of the engine brake.