Usage:
Several components have been changed for the 1991 model 3176 Engines. The 1991 engine has a 7LG serial number prefix for 3176 Truck Engines and a 43Z serial number prefix for engines in Challenger 75 Tractors. This article explains the major component differences only. Resultant component changes such as gaskets, O-ring seals, etc. are located in the Parts Manuals: SEBP1954 for 7LG1-Up 3176 Truck Engines and SEBP1941 for Challenger 75 Tractor Engines.
Installation of a 1991 3176...7LG Truck Engine into a chassis wired for an earlier 3176 ...2YG Truck Engine requires a 4P5880 Adapter Wiring Harness. If equipped with a Jake Brake ®, a solid state relay control is also required.
Unit Injectors
The 1991 electronic unit injectors have an eight-hole spray pattern compared to the earlier 2YG injector six-hole spray pattern The 4P1410 Injector is used on the 250 hp, 275 hp, and 300 hp 7LG engines. The 4P1420 Injector is used on the 325 hp 7LG, 43Z engines. Injectors are not interchangeable between 1991 7LG, 43Z and earlier 2YG engines.
Camshaft Assembly
The 1991 7E8426 Camshaft Assembly has a modified injector lobe ramp angle, a 7E8428 Solid Camshaft Drive Gear (earlier 2YG engines have a spring-dampened drive system), and requires a different 7E8430 Timing Ring and 7E8431 Idler Gear. The same camshaft assembly components are used on all 1991 7LG, 43Z engines. The camshaft assembly components are not interchangeable between 1991 7LG, 43Z and earlier 2YG engines.
Water Pump
The 1991 7E8554 (0R3195) Water Pump has a larger impeller and increased flow rate. The same water pump is used on all 1991 7LG, 43Z engines. The 0R3195 Water Pump is a service replacement for all engine models.
Coolant Manifold
The 1991 7E7909 Coolant Manifold is a one-piece aluminum manifold with improved flow rate capability and additional sensor/test ports. The 7E7909 Manifold requires a 7E7910 Regulator Housing Assembly, 7E8619 Bypass Tube, and miscellaneous gaskets. The 8N4485 Air Bleed Check Valve used on earlier 2YG engines has been removed from the 7E7909 Manifold. This requires all 1991 7LG, 43Z engines to have an OEM-installed vent line to the radiator top tank.
Oil Pump
The 1991 9Y8073 (0R3196) Engine Oil Pump has wider internal pump gears and increased flow rate. The 0R3196 Engine Oil Pump is a service replacement for the earlier 2YG 0R2826 Engine Oil Pump when used with a 9Y8071 Elbow.
Oil Cooler
The 1991 7LG, 43Z engines use three different sizes of oil coolers. The 250 hp, 275 hp, and 300 hp engines use a 7E6597 Oil Cooler (3.0 inch diameter tube and bundle). The 325 hp engine uses a 9Y3898 Oil Cooler (plate type) that is used on all earlier 2YG engines. The 325 hp 43Z engine uses a 4P3754 Oil Cooler (3.8 inch diameter tube and bundle). The oil coolers from the high horsepower engines may be installed on the lower horsepower engines for special applications when used with the correct end bonnets.
Piston Rings
The 1991 7LG, 43Z engines have an improved top piston ring and oil control piston ring. The 9Y8093 top ring has reduced face pressure at the ring ends. The 4P1659 oil control ring conforms better to the liner and has a stiffer oil control spring; improving oil control. The 1991 7LG, 43Z piston rings are service replacements for the earlier 2YG piston rings.
Turbochargers
The 1991 7LG, 43Z engines have a different turbocharger design. The major difference includes dual bearings, compressor wheel geometry, and turbine housing geometry. Several turbochargers are used on the 1991 7LG engine. Refer to the 3176 (7LG, 43Z) Parts Manuals for correct turbocharger part numbers. Turbochargers are not interchangeable between 1991 7LG, 43Z and earlier 2YG engines.
Electronic Control Module
The 1991 9X7154 (0R6127) Electronic Control Module (ECM) supplies a 12V signal to apply the engine compression brake (Jake Brake). The earlier 2YG 0R6149 ECM supplies a pulse width modulated signal to control the engine compression brake. The ECM's are not interchangeable between 1991 7LG, 43Z and earlier 2YG engines. The same ECM is used on all 1991 7LG, 43Z engines.
Personality Modules
The 1991 personality modules contain new control maps, diagnostic codes, and strategies. Diagnostic codes 01 "Override Of Idle Shutdown Timer", 28 "Check Throttle Sensor Adjustment ", and 51 "Intermittent Battery Power To ECM" have been introduced. Engines equipped with an inlet air temperature sensor have a diagnostic code 38 "Inlet Air Temperature Sensor Fault" and do not have diagnostic codes 37 "Fuel Pressure Sensor Fault" and 63 "Low Fuel Pressure Warning ", due to the removal of the fuel pressure sensor. The ECAP will display a warning "NOTICE" until the June 1991 NEXG4522 SPM is available.
There is a different personality module for 250 hp, 275 hp, 300 hp, 325 hp, 43Z 325 hp, and urban bus engines. Refer to the engine valve cover specification plate for correct personality module part numbers. Personality modules are not interchangeable between 1991 7LG, 43Z and earlier 2YG engines.
Engine Wiring Harness
The 1991 4P0498 Engine Wiring Harness has a 40-pin OEM connector (J7), a designated ECAP, DDT connector (P8), and supplies 5V to the coolant temperature sensor and inlet air temperature sensor (replaces fuel pressure sensor) through ECM connector P4 wire 10. The earlier 2YG engine wiring harness supplied 8V to the coolant temperature sensor through ECM connector P4 wire 30. The ECAP/DDT designated connector (P8) allows connection of an ECAP/DDT while the engine is running. The same engine wiring harness is used on all 1991 7LG, 43Z engines. The engine wiring harness is not interchangeable between 1991 7LG, 43Z engines and earlier 2YG engines.
Inlet Air Temperature Sensor
The 1991 7LG engine has an inlet air temperature sensor effective with engine serial number 7LG02259 (7X6182 Fuel Pressure Sensor has been removed). The 9X5370 Inlet Air Temperature Sensor is the same sensor used for coolant temperature. The senor controls fuel injection timing during cold inlet air/warm inlet air operation. The 9X5370 Inlet Air Temperature Sensor/Coolant Temperature Sensor is protected against electromagnetic interference. The 9X5370 Sensor is a service replacement for the earlier 2YG engine coolant temperature sensor.
Speed/Timing Sensors
The 1991 3E0487 Speed/Timing Sensor is more tolerant of timing ring runout and is protected against electromagnetic interference. The 3E0487 Sensor is a service replacement for earlier 2YG engine speed/timing sensors.
Jake Brake®
The 1991 7LG Jake brake has a new adjustment specification for the slave piston lash and a solid state relay control. The slave piston lash adjustment for 1991 7LG engines is increased to 1.27 mm (.050 in) to allow for correct valve-to-piston clearances due to the camshaft changes. The solid state relay control receives a 12V signal from the ECM to activate the Jake Brake. The earlier 2YG engines equipped with Jake Brakes use a pulse width modulated (PWM) electronic control system and optional dash control module. The Jacobs electronic control system and dash module are not interchangeable between 1991 7LG and earlier 2YG engines. The Jacobs part number 017596 Solid State Relay Group includes all electronic components to install the new control system.
