849838 Mercury SCREW, (.375-24 x 1.250)

Electronic Controls
The 3508 EUI Engine Electronic Control Module (ECM) consists of two main components: the control computer and the Personality Module. The Personality Module is the software for the control computer and also stores operating maps that define horsepower and torque curves. The two work together [along with sensors to "see" and injectors (EUI) to "act"] to control the engine. Neither one can do anything by itself.The ECM determines a "desired engine speed" based on the throttle switch and decelator signal and certain diagnostic codes. The ECM maintains the desired engine speed by sensing actual engine speed using the Speed/Timing sensor, then deciding how much fuel to inject in order to achieve the desired engine speed.Fuel Injection
The ECM controls the amount of fuel injected by varying signals to the injectors. The injectors will inject fuel ONLY if the injector solenoid is energized. The ECM sends a 105 volt signal to the solenoid to energize it. By controlling the timing and duration of the 105 volt signal, the ECM can control injection timing and amount of fuel injected.The ECM sets certain limits on the amount of fuel that can be injected. "FRC Fuel Pos" is a limit based on Fuel-Air Ratio, for smoke control purposes. When the ECM senses a higher turbo compressor outlet pressure (more air into cylinder), it increases the "FRC Fuel Pos" limit (allows more fuel into cylinder). "Rated Fuel Pos" is a limit based on the horsepower rating of the engine. It is similar to the rack stops and torque spring on a mechanically-governed engine. It provides horsepower and torque curves for a specific engine family and rating. All of these limits are programmed by the factory into the Personality Module, and are not programmable in the field.Injection timing depends on engine speed, load, and other operation factors. The ECM knows where top center of cylinder number one is from the signal provided by the engine Speed/Timing sensor. It decides when injection should occur relative to top center and provides the signal to the injector at the desired time.Programmable Parameters
Certain parameters that affect 3508 EUI Engine operation may be changed with the Electronic Control Analyzer Programmer (ECAP). The parameters are stored in the ECM and an audit trail is kept.These parameters are "System Configuration Parameters". System Configuration Parameters are those that are set at the factory and affect the performance of the engine.Passwords
"Logged Events" are protected by factory passwords. Factory passwords are calculated on a computer system available only to Caterpillar dealers.Section 2 Programming Parameters has more details on when passwords are needed and how to obtain them.Self-Diagnostics
The 3508 EUI Engine has some ability to diagnose itself. When a problem is detected, a Diagnostic Code is generated and a warning appears on the CMS display or Check Engine Lamp on retrofit applications. In most cases, the code is also stored in permanent memory in the ECM.Current Diagnostic Codes are referred to as ACTIVE. They indicate that a problem of some kind currently exists. They should always be serviced first. Refer to Section 4 Troubleshooting With a Diagnostic Code for more details.Diagnostic Codes stored in memory are called LOGGED. The problem may have been temporary or may have been repaired since the time it was logged. Therefore, logged diagnostic codes don't necessarily mean something needs to be repaired. LOGGED diagnostic codes may be helpful indicators for intermittent problems. In addition, to diagnostic codes the ECM also records "events", that have occurred rather than failures. Refer to Section 4 Troubleshooting With a Diagnostic Code for more details.Harness Wire Identification
The present type of wire identification, used on all Caterpillar equipment uses only eleven solid colors. In addition to only eleven basic colors of wire, a circuit number is stamped (put) on each wire. The circuit number is stamped approximately every inch for the length of the wire. The identification number for a circuit will be the same for any Caterpillar equipment.For example: A color code of "A701-GY" on the schematic would mean, there is a gray wire with the circuit number "A701" stamped on it. This wire is the solenoid signal wire (power) for cylinder No. 1 (CYLINDER HEAD SOL 1) on the Electronic Unit Injector (EUI) system wire harness. The "A701-GY" color code will be the identification of "SOLENOID 1 POWER" circuit on all Caterpillar equipment wire harnesses with Electronic Unit Injector (EUI) systems.Another wire identification on the schematic is the size of the wire. The size or gauge of the wire is called "AWG". The gauge of the wire will follow the wire color.For example: A color code of "150-OR-14" on the schematic would indicate the "150-OR" wire is a 14 AWG wire.If the gauge of wire is not listed after the wire color, the gauge of the wire will be 16 AWG.Diagrams
3508 EUI Electronic System D11N EUI System Diagram D11N EUI System Diagram for Retrofit Machines 3508 EUI System/CMS Display 3508 EUI System/CMS Display Functionality
CMS receives from the ECM information on engine oil pressure, jacket water coolant temperature, and engine speed over the CAT data link. This information can be viewed by the operator on the CMS display.The ECM can also tell CMS over the CAT data link when it has an ACTIVE diagnostic for the 3508 EUI system or an air filter restriction. CMS can turn on the correct lamp for the given condition. The service engine lamp will only be turned on when the ECM has an ACTIVE diagnostic for the 3508 EUI system.Refer to the CMS Service Manual (SENR5247) for more information on the CMS Display.The ECM does not know if the information it is sending is being received by CMS. Should there be a problem with communications between the ECM and CMS the following things can be observed on the CMS display:1. The Oil Pressure gauge will flash.2. The Coolant Temperature gauge will flash.3. The Tach will flash and a digital reading of 3000 rpm will be displayed.4. The Service Engine