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GM PFI

GM PFI. Operation and Testing. Overview. Operating Modes. Starting Clear Flood Run Acceleration Deceleration Battery Voltage Correction Fuel Cutoff. Starting Mode. PCM runs fuel pump for 2 seconds PCM looks at Coolant Temp and TPS A/F Ratio varies from 1.5/1 (-32F)

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GM PFI

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  1. GM PFI Operation and Testing

  2. Overview

  3. Operating Modes • Starting • Clear Flood • Run • Acceleration • Deceleration • Battery Voltage Correction • Fuel Cutoff

  4. Starting Mode • PCM runs fuel pump for 2 seconds • PCM looks at Coolant Temp and TPS • A/F Ratio varies from • 1.5/1 (-32F) • to 14.7/1 (201F) • May have cold start injector • Activated by cranking system • Controlled by timer

  5. Clear Flood • Below 600 RPM • 80% WOT or more • A/F 20/1 or zero on 2.8-liter engine

  6. Run Mode • Above 400 RPM • Open or closed loop • Closed loop when • O2S voltage is varying • Coolant is above specified temp • Time has elapsed • Leaves open loop for WOT Acceleration and hard Deceleration

  7. Acceleration Mode • Rapid increase in manifold pressure or air flow • Richer mixture • Compensates for poor evaporation due to higher pressure.

  8. Deceleration Mode • Rapid decrease in throttle and manifold pressure • Fuel is cut off completely momentarily

  9. Battery Voltage Correction Mode • Voltage drops below specified value • Enrichens fuel • Increases throttle opening if at idle • Increases dwell to account for poor coil saturation

  10. Fuel Cutoff Mode • Ignition is turned off • Distributor pulse stops • Fuel is cut off • Prevent dieseling • Prevent fire in crash

  11. Fuel Trim • Before OBD II • STFT was Block Learn • LTFT was Integrator • More in diagnostics

  12. Fuel Trim

  13. Inputs

  14. Mass Airflow • AC - Hot foil • Bosch - Hot wire with burn off • Hitachi - Heated thermistor • Frequency out • AC 30 Hz to 150 Hz

  15. Hall Pickup

  16. Hall Fast Start

  17. Hall CMP Distributor

  18. Reluctor

  19. Opti-Spark

  20. Opti-Spark

  21. EGR Diagnostic • Vacuum switch • Temp Switch • 5.0 and 5.7 engines • 12v when EGR off • 1v when EGR on

  22. EGR Diagnostic

  23. Outputs

  24. Injector Circuit

  25. SFI Injector Circuit

  26. Pintle VS Multec Injectors

  27. Cold Start Injector

  28. Cold Start Injector

  29. Cold Start Injector • Thermal Time Switch • In water jacket • 68F or below max 8 seconds • Less time with more temperature • Only while engine is cranking

  30. Idle Air Control • Stepper Motor • Zero and count pulses • Ingition off EFI • 30 MPH on PFI from VSS

  31. IAC

  32. IAC

  33. EGR • Early EGR was controlled by ported vacuum • Three types • Standard ported • Negative feedback pressure • Positive feedback pressure • Exhaust backpressure and vacuum

  34. EGR • EGR started in 1988 is Digital • Controlled by 2 or 3 solenoids • Solenoids control different size orifices

  35. Digital EGR

  36. Linear EGR • One Solenoid PWM 1994

  37. CMFI

  38. CMFI Distribution

  39. CMFI Injector

  40. CMFT Poppet

  41. Electronic Spark Control ESC • Timing modified by KS

  42. Conventional Injector Driver

  43. Peak and Hold Injector • Two Drivers

  44. PWM Injector

  45. Injector Cleaning • Areas needing cleaning • Spray surfaces • Inlet screens • Methods • Fuel tank additives • 3 part vacuum systems • Pressurized fuel rail

  46. Injector Testing • NOID light • Volt or ohm meter • Scope • Stethoscope • Injector Balance • Tester • Scan tool • Graduated cylinder

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