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

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

29. 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

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

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