3116 and 3126 HEUI Truck Engines Operating the Engine

Proper operation, driving techniques and maintenance are key factors in obtaining the maximum service life and economy of Caterpillar engines. Following the recommendations in this manual will lower operation costs. For more information, ask your Caterpillar dealer for LEDT2254, CAT Answers Your Questions About Truck Performance.


Idle speed is adjustable on Caterpillar electronic engines. Consult your Caterpillar dealer for information. The idle speed preset to 700 rpm.

Avoid excess idling. If the vehicle is parked for more than five minutes, STOP the engine. An engine can burn from 2.8 to 5.7 L (.7 to 1.5 US gal) of fuel per hour while idling. Excessive idling can cause excessive carbon buildup and/or slobber, which is harmful to the engine.

If extended idle time is required, control the engine speed to 1000 rpm or greater and take steps to ensure that the coolant temperature exceeds 82°C (180°F). Consult your Caterpillar dealer for assistance.

Fast idle can be programmed within the range of 700 to 1600 rpm. Fast idle requires an ON/OFF switch on the dashboard. Consult your Caterpillar dealer for assistance.

Idle Shutdown Timer

The idle shutdown timer can be programmed to shut the engine down after a specific time period of engine idling. The idle time can be programmed from 3 minutes to 1440 minutes (24 hours). If the idle shutdown timer is set to 0 minutes, the idle shutdown feature is disabled. If the timer setting is unknown, allow the engine to idle and observe how much time elapses before the engine shuts down. The following conditions must be met in order to activate the idle shutdown timer.

* The idle shutdown feature must be selected
* No vehicle speed is detected by ECM
* The engine is not under load
* The engine is at operating temperature (NOT in Cold Mode)

After the vehicle is stationary, the idle shutdown timer begins. The engine can be operating at low idle or at an idle rpm selected by the PTO governor. The CHECK ENGINE/DIAGNOSTIC (YELLOW) lamp will flash rapidly 90 seconds prior to shutdown. Movement of the vehicle automatically resets the idle shutdown timer to the programmed setting.

To override the idle shutdown timer:




The CHECK ENGINE/DIAGNOSTIC (YELLOW) lamp will flash rapidly 90 seconds prior to shutdown. Depress the service brake or the clutch pedal during the 90 seconds when the YELLOW lamp flashes.

After an idle shutdown, the engine can be restarted without turning the ignition key switch to the OFF position.

The override capability is disabled If the ALLOW IDLE SHUTDOWN OVERRIDE is programmed to NO.

Cold Mode Operation

Cold mode is initiated if the sum of the coolant temperature and the air inlet temperature is less than 35°C (95°F). In cold mode, the low idle is increased to 1000 rpm and the engine power is limited. The cold mode strategy provides reduced smoke emission and faster warm-up time.

Cold mode is deactivated when the temperature condition is met, or when the engine has been operating for 12 minutes.

After cold mode is completed, the engine should be operated at low rpm and low load until normal operating temperature is reached. The engine will reach normal operating temperature faster when the engine is operated at low rpm and low power demand than when then engine is idled with no load.

Cold mode is disabled if the throttle, the service brake, or the clutch (if equipped) is depressed. The cold mode operation rpm drops to the programmed low idle speed in order to allow the transmission to be put into gear.

Getting Started

Caterpillar electronic engines do not require long warm-up periods that needlessly waste fuel. Typically, the engine should be at normal operating temperature by the time the vehicle reaches the open road. Begin operating the engine at low load. After normal oil pressure is reached and the temperature gauges begin to rise, the engine may be operated at full load.

To get the vehicle in motion, use a gear that will result in a smooth, easy start in order to move the load without increasing the engine speed above low idle or slipping the clutch. Engage the clutch smoothly. Interrupted clutch slipping and abrupt clutch engagement put stress on the drive train and waste fuel.

Use progressive shifting techniques. Progressive shifting is using only the rpm required to make an upshift into the next gear. Progressive shifting improves fuel economy.

* Keep the engine rpm to a minimum. Use a low to mid range rpm (1400 to 2000 rpm)
* Use only enough rpm to pick up the next gear

Progressive shifting also reduces acceleration time. Top gear is reached sooner because it takes less time to synchronize gears during shifting and the engine is operating at its highest torque range.

The amount of rpm required to make an upshift increases as the vehicle speed increases, unless upshifts are made on upgrades. Experience with the vehicle will show you how much rpm is required to make upshifts under various conditions.

NOTE: These engines may be programmed to encourage progressive shifting. If acceleration rates slow dramatically when certain speeds (rpm) are reached while driving in the lower gears, shift parameters have been programmed into the ECM. Shift parameters will limit rpm white driving in higher gears. These parameters are protected by customer passwords.

If the vehicle can be operated in a higher gear after the desired vehicle speed is reached, select the highest gear available that will pull the load. By following this recommendation, fuel economy can be obtained. The engine will be operating at the lowest rpm required to pull the load.

Vehicle Efficiency

An efficient vehicle performs the desired amount of work while minimizing the power demand on the engine. The following factors are major contributors to power demand.

* aerodynamic drag (wind resistance)
* rolling resistance of the tires
* gross weight of the vehicle
* losses in the drive train and the load from the engine driven accessories

For more information about vehicle efficiency, refer to LEDT2254, CAT Answers Your Questions About Truck Performance.

Fuel Economy

Fuel is the largest single operating cost of today’s on-highway vehicle engines. Improved fuel economy can have a substantial impact on operating profit. The most significant factors that influence vehicle fuel economy are:

* Driver techniques
* Vehicle efficiency
* Operating conditions
* Engine efficiency

A No.1 grade of fuel contains less energy per volume and will increase fuel consumption because a greater volume of fuel must be injected in order to yield the same amount of work as a No.2 grade of fuel. The difference in fuel economy between a No.1 grade of fuel and a No.2 grade of fuel can be as great as 0.2 to 0.3 km/L (.5 to .7 mpg).

For more information about fuel economy, refer to LEDT2254, CAT Answers Your Questions About Truck Performance.

Rolling hills provide great opportunity to reduce fuel consumption. Avoid downshifting on small hills. Even if the engine must be lugged to speeds below peak torque rpm, the vehicle should not be downshifted. When going down a hill, use gravity instead of the engine’s power to regain vehicle speed.

On grades that require more than one downshift, let the engine lug to peak torque rpm. If road speed stabilizes with the engine running at or above peak torque rpm, remain in that gear.

Long steep down grades should be anticipated. Vehicle speed should be reduced before cresting the top of a hill and proceeding down a long steep grade. Minimize the amount of braking that is used to maintain a safe speed in order to maximum fuel efficiency.

The engine’s ability to hold the vehicle back increases with engine speed. A gear should be selected that runs the engine near the high engine rpm limit for long steep hills when braking is required.

Speed reductions and future stops should be anticipated. Downshifts should be avoided and the amount of braking minimized in order to improve fuel consumption. By coasting to a stop, a considerable distance can be traveled without consuming any fuel.


The faster a vehicle is driven, the more fuel it will consume. Increasing cruising speed from 88 to 104 km/h (55 to 65 mph) will increase fuel consumption of a typical Class 8 vehicle approximately 0.4 km/L (1 mpg). Driving faster to increase stop time makes those stops very expensive. Cruising time provides the greatest opportunity to benefit from operation in the most efficient rpm range of the engine (1400 to 2000 rpm).

Cruise Control

Depending upon the vehicle manufacturer, the Cruise Control switch may be programmed to operate in one of two modes:

* The SET position may operate as SET/ACCEL or SET/DECEL
* The RESUME position may operate as RESUME/ACCEL or RESUME/DECEL

Refer to the markings on the Cruise Control switch or refer to your Truck Owners Manual.

To set the Cruise Control:


After you accelerate to the desired speed, turn the Cruise Control ON/OFF switch ON.


Press the SET/RESUME switch to the SET position.

The ECM will control the vehicle speed until the clutch pedal or the service brake is depressed or the Cruise Control ON/OFF switch is turned OFF.

NOTE: You can also accelerate to desired speed and set the cruise control speed by pressing the SET/RESUME switch to the ACCEL position.

To resume speed after an after an interruption:

* Press RESUME and the vehicle will return to the “set” speed.

Momentarily pressing or “bumping” the SET/RESUME switch to the ACCEL position will increase vehicle speed by one mph. Press the switch to the DECEL position to decrease speed by one mph. The operating range of the cruise control has been programmed into the ECM.

SoftCruise Control

The Cruise Control can be programmed to operate in one of two modes, SoftCruise = YES or SoftCruise = NO.

SoftCruise provides an eight km/h (five mph) operating range around the cruise control setting. Engines are shipped from Caterpillar programmed to operate in SoftCruise = YES. SoftCruise allows the vehicle to accelerate slightly, under power, going down hills and get a “run” at the next hill. Improved fuel economy can be gained in this mode.

When SoftCruise = NO is programmed, the SET speed is maintained. Consult your Caterpillar dealer for more information.

Idle/PTO Governor Mode

The cruise control function of the electronic engine works as an engine speed governor when the vehicle is stationary or when operated at a vehicle speed below the Idle/PTO Vehicle Speed Limit. Activation and deactivation of the engine speed governor is the same as for the cruise control.

The engine speed governor will operate at any engine rpm from low idle to the maximum Idle RPM Limit (which is usually less than rated engine rpm). The maximum Idle/PTO governor speed is a Customer Specified Parameter.

To Activate Idle/PTO Governor Mode:


Set the cruise control ON/OFF switch to the ON position. The throttle can then be used to determine the desired engine rpm.


When the desired engine rpm is reached, place the SET/RESUME switch to the SET position and release the switch. The engine rpm will be maintained at this speed.

NOTE: If the SET/RESUME switch is held for more than one second in the ACCEL position, the ECM will increase the engine rpm until the SET/RESUME switch is released. The ECM will increase the engine rpm up to the Idle/PTO Engine rpm Limit, if programmed, or to Top Engine Limit (TEL).

To Disengage the Idle/PTO Governor Mode:

* Move the Cruise/Idle/PTO ON/OFF switch to the OFF position, or
* depress the clutch pedal, or
* depress the service brake pedal

To Resume the Idle/PTO Governor Mode:


Ensure that the Cruise/Idle/PTO ON/OFF switch is in the ON position.


Move the SET/RESUME switch momentarily to the RESUME position.

NOTE: If the SET/RESUME switch is held for more than one second in the DECEL position, the ECM will decrease the engine rpm until the switch is released. A new set rpm is established when the switch is released.

Uphill Operation

For optimum performance, allow the engine to lug down to peak torque speed (1440 to 1550 rpm) before downshifting. Continue to downshift in this manner until you reach a gear that maintains the desired speed. Continue to operate at a low (1440 to 1550) rpm if the vehicle will make it to the top without a downshift. Begin upshifting as the grade of the hill decreases and the engine begins to accelerate above 2000 rpm. Driving this way will provide optimum fuel economy and performance.

NOTE: Allowing the engine to lug below peak torque is permissible if the vehicle is cresting the top of a hill. However, extended operation at engine speeds below peak torque (usually 1400 rpm) will raise the exhaust temperature and the cylinder pressure. This can lead to reduced engine service life.

Downhill Operation

On a downgrade, do not coast with the clutch pedal depressed or with the transmission in NEUTRAL. If you do not want to use power, disengage the Cruise Control.

Select the correct gear that does not allow the engine speed (rpm) to exceed 2900 rpm and use the service brakes to control the speed of the vehicle. A basic rule is to select the same gear that would be required to go up the grade. Refer to the rated (full load) rpm on the engine Information Film.

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