Good info g8 gt part 3 of 4
Originally introduced on the Gen III Vortec V8s, returnless fuel injection represented a paradigm shift for GM, developed to improve performance and decrease evaporative emissions. Previously, Vortec 6.0Ls used a return line between the engine and the fuel tank to manage fuel pressure by bleeding off excess fuel at the fuel rail and returning the excess to the tank. The new system eliminates the return lines and moves the fuel pressure regulator from the fuel rail on the engine to the fuel tank. Because it delivers only the amount of fuel needed by the injectors, and returns no fuel to the gas tank, the returnless system essentially eliminates heat transfer from the engine to tank. This reduces the amount of vapor generated in the tank and captured by the vehicle’s Onboard Refueling Vapor Recovery (ORVR) system.
With the returnless system, the 6.0L (L76) uses a fuel rail manufactured of stainless steel. Previous versions used a nylon rail. The stainless steel rail allows installation of baffles that manage fuel pulses in the returnless system and reduce noise.
Advanced Electronic Throttle Control
GM Powertrain has led the industry in applying electronic throttle control (ETC) to its V8s, and all applications of the Gen IV are now equipped with ETC. The Gen IV 6.0L (L76) introduces the next generation ETC.
With ETC, there is no mechanical link between the accelerator pedal and the throttle body. A sensor at the pedal measures pedal angle and sends a signal to the engine control module (ECM), which in turn directs an electric motor to open the throttle at the appropriate rate and angle. ETC delivers a number of benefits to the customer. Besides throttle pedal angle, the ECM measures other data, including the transmission’s shift patterns and traction at the drive wheels, in determining how far to open the throttle. ETC delivers outstanding throttle response and greater reliability than a mechanical connection, which typically uses a cable that requires adjustment—and sometimes breaks. Cruise control electronics are integrated into the system, further improving reliability and simplifying engine assembly.
The Gen IV 6.0L (L76) takes ETC to the next level by taking advantage of capability built into its advanced E38 ECM (below) and further streamlining the system. Its up-integrated ETC system eliminates a Throttle Actuator Control (TAC) module. The previous TAC takes commands from the ECM and then operates the electric motor that opens and closes the throttle. The E38 manages the throttle directly, without a TAC. Eliminating the TAC reduces cost and improves reliability. The direct link between the ECM and the throttle motor improves throttle response time (albeit in millisecond increments that are not apparent to the driver) and improves system security by removing a device (the TAC) that must be monitored for malfunction
E38 Engine Control Module
An advanced controller manages the multitude of operations that occur within the 6.0L (L76) every split second. The E38 is the mid-line controller in GM Powertrain’s family of engine control modules (ECM), which direct nearly all the engines in Powertrain’s line-up. In combination with advanced sensor technology, the E38 includes the ability to control and synchronize advanced technologies such as Active Fuel Management.
The E38 features 32-bit processing, compared to the conventional 16-bit processing in previous V8 engines. The E38 operates at 59 MHz, with 32 megabytes of flash memory, 128 kilobytes of RAM and a high-speed CAN bus, and it synchronizes more than 100 functions, from spark timing to cruise control operation to traction control calculations. The E38 works roughly 50 times faster than the first computers used on internal combustion engines in the late 1970s, which managed five or six functions.
The family strategy behind GM’s new ECMs allows engineers to apply standard manufacturing and service procedures to all powertrains, and quickly upgrade certain engine technologies while leaving others alone. It creates both assembly and procurement efficiencies, as well as volume sourcing. In short, it creates a solid, flexible, efficient engine-control foundation, allowing engineers to focus on innovations and get them to market more quickly. The family of controllers means the ECM and corresponding connectors can be packaged and mounted identically in virtually every GM vehicle. Powertrain creates all the software for the three ECMs, which share a common language and hardware interface that’s tailored to each vehicle.
The E38 also applies a rate-based monitoring protocol sometimes known as run-at-rate diagnostics. Rate-based diagnostics improve the robustness of the Onboard Diagnostics System (OBD II) and ensure optimal performance of emissions control systems. The new software increases the frequency at which the ECM checks various 6.0L (L76) systems, and particularly emissions-control systems such as the catalytic converter and oxygen sensors. Rate-based diagnostics more reliably monitor real-word operation of these systems, and allow regulatory agencies to more easily measure and certify emissions compliance.
58X Ignition System
The 6.0L (L76) has an advanced 58X crankshaft position encoder to ensure that ignition timing is accurate throughout its operating range. The new 58X crankshaft ring and sensor provide more immediate, accurate information on the crankshaft’s position during rotation. This allows the E38 ECM to adjust ignition timing with greater precision, which optimizes performance and economy. Engine starting is also more consistent in all operating conditions.
In conjunction with 58X crankshaft timing, the Gen IV V8s apply the latest digital cam-timing technology. The cam sensor is now located in the front engine cover, and it reads a 4X sensor target on the cam sprocket. The target ring has four equally spaced segments that communicate the camshaft’s position more quickly and accurately than previous systems with a single segment. It provides precise control required for variable valve timing.
The dual 58X/4X measurement ensures extremely accurate timing for the life of the engine. Moreover, it provides an effective back-up system in the event one sensor fails.
Enhanced Noise, Vibration and Harshness Control
The Gen IV V8s were developed for quieter operation, with virtually every system or component reviewed in an effort to reduce noise, vibration and harshness. Quiet features built into the engines are complemented by improved engine cradles and mounting systems. These help reduce vibrations transmitted through the chassis and into the passenger compartment.
The NVH enhancements include floating pin pistons, which reduce noise and increase durability. These pistons have wrist pins that “float” inside the rod bushing and the pin bores in the piston barrel. Compared to a conventional fixed pin assembly, in which the connecting rod is fixed to the piston’s wrist pin and the pin rotates in the pin bore, the floating pins reduce stress on the pin. They allow tighter pin to pin-bore tolerances and reduce noise generated as the piston moves through the cylinder. To further reduce wear, the pistons are coated with a polymer material, which limits bore scuffing, or abrasion of the cylinder wall over time from the piston’s up-down motion. The polymer coating also dampens noise generated by the piston’s movement. The result for the customer is less engine wear, improved durability and quieter operation.
The Gen IV V8s also feature a new heavy-duty timing chain developed expressly for quiet operation. The chain, which connects the cam and crankshaft, is validated for 200,000 miles of operation and fitted with a new leaf-spring dampener. Even the most durable chains stretch with time. In many engines they must be adjusted or replaced at scheduled intervals. The chain dampener on the 6.0L (L76) maintains optimal chain tension for the life of the engine and eliminates any flapping motion that might develop as the chain stretches with mileage. It ensures that the timing chain operates as smoothly and quietly as new, even as the engine accumulates high mileage.