COMPUTERS AND INPUT SENSORS

1. COMPUTERS AND INPUT SENSORS CHAPTER 8

2. VOLTAGE SIGNALS Pg 153C • ANALOG VOLTAGE SIGNALS • VARIABLE VOLTAGE SIGNAL • COMPUTERS INPUTS ARE USUALLY ANALOG TYPE SIGNALS • EASY TO DIAGNOSE WITH DVOM • DIRECT CURRENT OR ALTERNATING CURRENT

3. DIGITAL VOLTAGE SIGNALS Pg 154C • VOLTAGE IS EITHER HIGH OR LOW IN A GIVEN TIME PERIOD • COMPUTER USES AND PROCESSES INFORMATION IN DIGITAL LANGUAGE (BINARY 0 or 1) • SOME INPUTS PRODUCE A SQUARE WAVE SIGNAL

4. Pg 155C COMPUTER OPERATION • INPUT CONDITIONING • AMPLIFICATION • ANALOG TO DIGITAL CONVERSION • SOME A/D CONVERTER EXTERNAL TO MAIN PROCESSOR. (LIKE FORD PROGRAMMABLE SPEED ONLY MEMORY - PSOM)

5. COMPUTER MEMORY Pg 159C • RAM - RANDOM ACCESS MEMORY • TEMPORARY STORAGE • VOLATILE OR NON-VOLATILE • ROM - READ ONLY MEMORY • PROM - PROGRAMMABLE READ ONLY MEMORY • TELLS MICROPROCESSOR HOW VEHICLE IS EQUIPPED

6. COMPUTER PROGRAMMED STRATEGY Pg 160C • OPEN LOOP - CLOSED LOOP • ADAPTIVE STRATEGY • ABILITY OF COMPUTER TO LEARN FROM PAST EXPERIENCE. • COMPENSATES FOR WEAR • Will lose learned strategy if: • BATTERY DISCONNECTED • WHEN MAJOR COMPONENT REPLACED • NEW VEHICLE

7. INPUT PROCESSING • ROM LOOK UP TABLES (Pg 162C) • COMPUTER TAKES ALL INPUT INFO BEFORE MAKING DECISION • ONE WIRE INPUT (Pg 140L & 154L) • TWO WIRE INPUT (Pg 142L & 143L) • THREE WIRE INPUT (Pg 144L) • FOUR WIRE INPUT (Pg 146L)

8. PINPOINT TESTING • MOST REPAIR MANUALS TELL TO CAUSE OPPOSITE CODE • OHMMETER VS. VOLTMETER • FREQUENCY INPUT TESTING • LAB SCOPE USE • BLOCK LEARN - INTEGRATOR

9. OXYGEN SENSORS • 1,2,3,4 Wire s • EGO, HEGO • Lean Low Volts • Rich High Volts • Zirconia Type • Titania Type • DVOM or Lab Scope Only!!! PAGE 168C

10. ECT/ACT SENSORS PG 142L • THERMISTORS HIGH RESISTANCE COLD AND LOWER RESISTANCE HOT

11. THROTTLE POSITION SENSORS (TPS) PG 145L • ROTARY AND LINEAR • MUST BE SMOOTH VOLTAGE CHANGE • BEST TO USE A LAB SCOPE FOR TEST

12. THROTTLE SWITCH Pg 146L • Four Wire Sensor • Used on alot of Foreign Cars and Trucks • Adjustment is critical • Some switches used as Fuel Pump Shut Off

13. MANIFOLD ABSOLUTE PRESSURE SENSOR Pg 147L • Senses differences between atmospheric pressure and manifold vacuum. • Must use specialized equipment to test • Sometimes used for BARO Input information

14. VANE TYPE Commonly used on foreign Cars Test with DVOM or Lab Scope Plate movement proportional to Air Flow Other Inputs HOT WIRE TYPE or GRID TYPE Use Frequency Test Map Frequency should always be a straight line transition with rpm. Tap Test MASS AIR FLOW SENSORS Pg 151L Pg 152L

15. KNOCK SENSORS • PIEZOELECTRIC CRYSTAL • Produces a frequency and changes it to a voltage before sending to PCM • TAP TEST, DVOM, FREQ or OHMMETER

16. EGR SENSORS Pg 154L Pg 317L • EVP Linear Sensor • Must test mechanical and electrical • Many different types of EGR & ``EGR Controls and EGR Sensors • Most EVP’s send a Analog signal • Lots of Driveability Problems • EGR problems can be caused by other Inputs

17. VEHICLE SPEED SENSORS • AC SIGNAL (ANALOG) • LOCATED DIFFERENT PLACES • SPEED BUFFER OR PSOM • CAN CAUSE TCC, CRUISE, SPEEDOMETER PROBLEMS

18. NEUTRAL DRIVE SWITCH

19. OUTPUTS • ACTUATORS • SOLENOIDS • RELAYS • DISPLAYS • CONTROLLED BY DRIVERS • TRANSISTORS OR GROUPS OF TRANSISTORS

20. STUDY HARD AND ABSORB!!