Originally Posted by hog

The new PCM is roughly the same size as the PCM it replaces and is installed in the same place as the previous PCM in various applications—in all applications on the firewall or inner fender, depending on the vehicle. There is no visible difference in the engine bay.

IMPROVED DENSO OXYGEN (O2) SENSORS
The Vortec 8100 has new oxygen (O2) sensors. These O2 sensors have the same 6.6-volt heat rating as the parts they replace, allowing them to achieve closed loop operation—and maximum exhaust emissions reduction--in minimum time. The new sensors allowed engineers to implement the current monitoring function provided by the new PCM, and they are common to other truck gasoline V8s.

SOLID STATE OIL-PRESSURE SENSOR
The 8.1L now has a fully electronic, solid-state oil pressure sensor, replacing an analog/mechanical sensor. The solid-state sensor is installed in the same location in the engine block, but it has no mechanical parts, increasing reliability. Its introduction coincides with a new electronic instrument package in some applications.

REVISED ELECTRONIC THROTTLE BODY
The Electronic Throttle Control (ETC) system on the 8.1L uses a new throttle body and Throttle Actuator Control (TAC) module. The throttle body’s diameter (75 millimeter) has not changed, but the new part features a ``wrap around’’ throttle motor. The electric motor that operates the throttle plate is literally built around the throttle body and responds more quickly to commands from the TAC. The new throttle body is now common to all gasoline-powered GM truck V8s.

Before the Vortec 8100, ETC was largely reserved for premium passenger car engines and some heavy duty trucks. There is no mechanical link between the accelerator pedal and the throttle. Besides throttle pedal angle, the PCM measures other data, including the transmission's shift points, in determining how far to open the throttle. ETC delivers outstanding throttle response and can be calibrated to match demands in different applications.

COOLANT FLOW FROM HEATER CORE REVISED ON SILVERADO AND SIERRA
In the 8.1L applications, the flow pattern for engine coolant has been revised to heat the cab more quickly during cold temperature operation.

The heater core is a small radiator inside the vehicle’s instrument panel, behind the engine firewall. Hot coolant from the engine flows through the heater core, where the ventilation fan forces heat through ductwork to the dash vents and into the cab. In extremely cold temperatures, large displacement engines such as the 8.1L can take some time to reach a temperature sufficient to heat the cab. GM engineers have developed a simple, effective method to increase customer comfort by shortening the time it takes to heat the cab.

On Silverados and Sierras, the heater return hose is now routed into the radiator return hose rather than the radiator itself. That means the coolant flowing in and out of the heater core bypasses the radiator, where coolant is at its coldest temperature anywhere in the cooling system. Coolant flowing to the heater core stays out of the radiator until the engine reaches full operating temperature and the thermostat opens. This allows the cab to heat more quickly, meeting GM’s stringent time standard, without reducing cooling capacity during high-temperature operation.

2004
LOW PERMEABILITY INTAKE MANIFOLD AND THROTTLE BODY GASKETS
The Vortec 8100 has new intake manifold sealing gaskets manufactured from a fluorocarbon material. These fluorocarbon gaskets represent the best sealing technology available. The gaskets are resistant to most chemicals, for maximum durability, and particularly impermeable to small hydrocarbon molecules. Gasoline vapor cannot penetrate the fluorocarbon. Moreover, the gaskets are designed to improve sealing for the life of the engine. They are molded with slight protrusions, or ``snouts,’’ that fit into counter-bores milled in the cylinder heads. The snouts more positively locate the gaskets and virtually eliminate the possibility of movement during assembly or after repeated thermal cycling over the life of the engine.

IMPROVED ONBOARD REFUELING VAPOR RECOVERY (ORVR) SYSTEM FOR CHEVROLET AVALANCHE AND SILVERADO, GMC SIERRA AND YUKON XL
The ORVR system on these Vortec 8100-equipped vehicles uses a new evaporative emissions canister and purge-control solenoid. ORVR reduces evaporative emissions by preventing gasoline vapor from escaping into the atmosphere during refueling. These new ORVR components take full advantage of advanced technology built into the Vortec 8100's P59 Powertrain Control Module (PCM). The PCM and new components more efficiently manage ORVR, and improve the accuracy and robustness of the OBDII (On-Board Diagnostics) system. This precision will reduce the number of false alarms – OBDII ``service engine’’ warning lights – that require dealer intervention.

With improvements to ORVR, the returnless fuel injection and low-permeability gaskets, the Vortec 8100 meets new, near-zero evaporative emissions standards mandated for 2004.

EXHAUST GAS RECIRCULATION (EGR) ELIMINATED
The EGR control valve and plumbing have been removed from all Vortec 8100s. The EGR system was used to recycle some exhaust gas back into the intake stream to cool combustion and reduce oxides of nitrogen (NOx) emissions. Data from development and durability test vehicles indicates that software refinements in the P59 PCM, and the engine’s overall efficiency, allow the Vortec 8100 to meet all 2004 North American exhaust emissions standards without EGR. Removing EGR reduces cost, complexity and potential warranty claims, improving both assembly efficiency and reliability.

IMPROVED CRANK AND CAM TIMING SENSORS
Vortec 8100s are equipped with new crankshaft and camshaft timing sensors. The sensors continue to operate on the Magnetic Reluctance (MR) or “mirror image” ignition timing principle, ensuring precise measurement over the life of the engine without adjustment. These sensors are now common with those used on other Vortec V-8s, helping streamline purchasing requirements, reducing inventory requirements and increasing efficiency at engine assembly plants.

IMPROVED CRANKSHAFT SEAL
The Vortec 8100 has a new front engine cover with a redesigned crankshaft seal. The seal requires no particular orientation during installation. It reduces engine assembly time and virtually eliminates the possibility of misalignment.

ADJUSTABLE THROTTLE PEDAL FOR WORKHORSE CUSTOM CHASSIS
WCC commercial vehicles will be offered with a throttle pedal that can be moved to accommodate different drivers. Vortec 8100s built for this application require PCM software recalibration to manage the electronic throttle control. There are no hardware changes.

REVISED CYLINDER HEADS FOR INDUSTRIAL APPLICATIONS
Vortec 8100s built for industrial use have new valve and valve seat material and new springs. Industrial engines typically operate at relatively low, steady rpm (1800-2000), creating different demands than the typical truck duty cycle. The valve seats in industrial Vortec 8100s have been metallurgically improved with induction hardening, and valve-spring tension has been reduced to soften valve interaction with the seats during low speed operation. Finally, industrial engines are now equipped with the same Silcrome 1 valves used in Vortec 8100s built for trucks. This material includes tungsten, vanadium, manganese and silicone, with higher chromium content than conventional iron valve alloy. The Silicrome 1 valves ensure long-term durability in industrial engines and increase efficiency at the engine plant by reducing inventory.