Electronic fuel injection control system ­ Both the normal (L56) and heavy-duty emissions certified (L65) versions of GM's turbo diesel engine utilize an electronic fuel-injection control system. This major technological enhancement incorporates a powertrain control module (PCM) that controls both the engine and transmission, an electronic throttle control and an electronically controlled fuel-injection pump. The adaptation of electronics to the rotary injection pump yields almost complete freedom to schedule fuel quantity and timing at optimal values for every speed and load point. What does all of this mean to the customer? Increased fuel economy, the elimination of black and white exhaust, improved cold weather starting, enhanced idle quality and reduced noise levels. The electronic fuel delivery system also helps protect the engine from overheating and other abuses, and allows GM to be fully compliant with current emissions standards. GM was the first manufacturer to introduce an electronically controlled fuel injection system in diesel pickup trucks.

The fuel injection pump was upgraded in 1997 and again in 1999 for improved durability by improving the Optical Sensor Tracking Encoder (OSTE) circuit board. In addition, the steel rollers in the pump were replaced with ceramic rollers for longer life. This system also makes available three electronically controlled Power Take Off (PTO) speeds. They are 1070 RPM, 1360 RPM, and 1600 RPM. These speeds can be activated by a simple switch.

Turbocharging ­ When GM set out to design the 6.5L V8 diesel engine, the goal was to build an engine that was reliable and durable, with unparalleled performance. From the start, the 6.5L was designed specifically for turbocharging. The secret weapon behind the 6.5L turbo diesel is the GM computer controlled wastegate. This wastegate allows the turbocharger rotor speed and boost to be electronically adjusted as altitude and engine speed change, and as torque is needed. The wastegate helps the engine work harder, but only when it needs help. When you need torque, it's there; when it's not required, the wastegate does not overwork the engine. The payoff is impressive fuel mileage, smooth, quiet operation and the necessary power to complete the job. This uniquely designed wastegate turbocharger delivers quick throttle response during acceleration and reduces turbo-boost pressure after obtaining maximum torque. The wastegate is designed to prolong turbo life and help manage the overall stress on internal engine components.

On-Board Diagnostics Second Generation (OBDII) ­ As with all GM vehicles, GM's L56 and L65 turbo diesel engine is fully OBDII compliant. This required significant enhancements to the powertrain control module (PCM). The PCM, a highly sophisticated on-board computer, received a 50-percent increase in memory and improved diagnostic capabilities in 1996. The PCM, which began controlling the fuel-lift pump and air conditioner in 1996, also monitors sensor systems such as coolant temperature, fuel temperature, air temperature, barometer, exhaust gas recirculation (EGR) pressure, turbo boost pressure and the thermostat diagnostic. This technology will help GM vehicles meet the new, more stringent emissions regulations, as well as improve idle stability. Misfire detection was added to OBDII in 1998.

Turbocharging system ­ On the G-van application of the L65, a center mounted turbocharging system shortens the air and oil passages and provides direct flow from the block. This design eliminates the need for oil lines, which increases reliability, durability, and serviceability. Oil is fed and drained directly from the block mount. Fuel-manager filter system ­ Each of GM's diesel engines feature the fuel-manager filter system. This system is a double-filtration fuel filter that incorporates the filter, a water separator and a fuel heater all in one canister. The top-load vertical design and location simplify filter cartridge replacement.

Common serpentine accessory belt drive ­ The 6.5L V8 diesel engine features a single serpentine belt for all the driven components. Its automatic tension adjuster improves belt life and makes servicing easier.

Fuel economy ­ Among the many superior characteristics of the 6.5L turbo is its exceptional fuel economy. When matched against a comparably performing big-block V8 gasoline engine, this diesel has the potential for 25 to 80 percent better fuel economy. The improved fuel economy is a result of precise control of combustion and more precise transmission control, both due to electronic control.

Crankshaft bearings ­ The crankshaft bearings used in the 6.5L are made of a fatigue-resistant material that promotes a higher bearing stress life. The rear crankshaft seal is in one piece to reduce the chances of leakage.

Bulkhead ­ The 6.5L diesel engine bulkhead area is designed to handle the higher-cylinder firing pressures of a turbocharged engine. In addition, the coolant passages and the oil galleries are sized to provide the increased flow required by a turbo engine.

Combustion chamber ­ To provide smokeless performance and meet stringent emissions standards without sacrificing power, the 6.5L is designed with an optimized combustion chamber. This design provides an optimum balance of air in the prechamber, head and cylinder that ensures a more even and complete burning of fuel. For 1999 the compression ratio has been reduced to 19.5:1 and an exhaust pressure regulator system was added to eliminate white smoke.

Modulated exhaust gas recirculation system ­ In addition to having an optimized precombustion chamber, the 6.5L L56 turbo engine utilizes an electronically controlled modulated exhaust gas recirculation system. This allows for more precise control over the flow of exhaust gas and also helps to meet stringent emissions standards.

Adaptive cylinder balance ­ Adaptive cylinder balance is included on the 6.5L turbo diesel. This process measures the horsepower of each cylinder at idle and directs fuel to each cylinder accordingly. This results in smoother operation of the vehicle by minimizing the vibration of the engine.

Cylinder block ­ The cylinder block incorporates piston spray cooling for increased engine life. This is accomplished by installing spray nozzles in the bulkhead that spray of oil at the underside of the piston. An increased flow oil pump and lubrication system ensure sufficient oil pressure during all running conditions. The oil cooler lines and oil coolers have increased in size so that they provide a 100% increase in flow through the oil cooler.

Cooling system ­ The cooling system has been upgraded with an increased flow water pump and new water crossover and dual full-blocking thermostats. For 1999 the water pump bearing has been improved for greater durability.

Catalytic converter ­ The catalytic converter was removed for 1999 while continuing to meet all emission requirements.

Oil pan capacity ­ In 1999 the oil pan capacity increased to eight quarts, which reduces maintenance.