1. Modern Automotive Technology PowerPoint for by Russell Krick
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

2. Chapter 23
Gasoline Injection
Diagnosis and Repair

3. Contents Gasoline injection problem diagnosis
Fuel pressure regulator service
Injector problems
Throttle body injector service
Servicing EFI multiport injectors
Engine sensor service
Control module service
Gasoline injection adjustments
Testing idle control motor
Multiport throttle body service

4. Gasoline Injection Problem Diagnosis
To diagnose problems in injection systems, you must use:
your knowledge of system operation
your troubleshooting skills
a service manual
a scan tool on recent vehicles

5. Diagnostic Steps Verify the problem or complaint
Perform a general (visual) inspection:
hoses and vacuum lines
wires
injection system components
leaks
connections
Use on-board diagnostics

6. Look for loose wires, leaking hoses, and other obvious problems
Visual Inspection
Look for loose wires, leaking hoses, and other obvious problems

7. Injection Problems
Evaluate the symptoms and narrow the list of components that could be at fault

8. Check electrical connections closely
EFI Diagnosis
Check electrical connections closely

9. On-Board Diagnostics
Most electronic fuel injection systems have on-board diagnostic capabilities
Control module can detect a bad component and produce a diagnostic trouble code
The malfunction indicator light (MIL) may be illuminated to tell the driver or technician that a fault exists

10. Scan Tool Use
A scan tool will find and display many electronic fuel injection problems
allows the technician to scan for DTCs
input sensor values may be monitored
output device status may be monitored or even overridden for diagnostics
The scan tool is connected to a data link connector under the dash or in the engine compartment

11. Scan Tool
Detects lean or rich operation, misfiring, sensor circuit and actuator problems
Used to find problems in the EFI system

12. OBD II Fuel System Monitoring
Checks for stoichiometric fuel mixture
Feedback from the upstream oxygen sensor is used as the primary indicator of fuel mixture

13. Fuel System Monitoring
If the O2 sensor signals a poor fuel mixture, the control module will:
temporarily adjust injector pulse width to correct the mixture (short term fuel trim)
if necessary, permanently adjust injector pulse width (long term fuel trim)
turn on MIL and set a DTC if allowable parameters are not met

14. OBD II Oxygen Sensor Monitoring
Checks upstream and downstream oxygen sensor for abnormal voltage and slow response
Oxygen sensors are heated to speed warm-up
Heater monitor checks the heating element in the sensors

15. EFI Testers Some early EFI systems don’t have on-board diagnostics
An EFI tester may be used to locate system problems
Connected to the wiring harness, this tester uses indicator lights to signal circuit status

16. Oscilloscopes
Used to view electronic waveforms at the EFI injector circuits
Excellent tool for injector, harness, and control module diagnosis

17. Fuel Pressure Regulator Service
Faulty system may cause rich or lean mixtures
if the pressure is too high, the mixture will be too rich
if the pressure is too low, the mixture will be too lean

18. Relieving System Pressure
Many injection systems maintain fuel pressure after the engine is shut off
Always relieve pressure before opening the system
High fuel pressure could cause fuel to spray out with great force, causing injury or fire

19. Relieving System Pressure
The procedure for relieving pressure depends on the system design:
use the pressure relief valve
apply vacuum to the pressure regulator
disable the fuel pump; then start and idle the engine until it stalls from lack of fuel

20. Relieving System Pressure
Applying vacuum to the regulator may relieve fuel pressure

21. Fuel Pressure Checks
Connect a gauge to the Schrader valve or in the fuel line feed to the injection system
Start the engine and note the fuel pressure

22. Pressure should be within specifications with the engine running
Connecting the Gauge
Pressure should be within specifications with the engine running

23. Causes of Low Fuel Pressure
Fuel filter
test fuel pressure “before” the filter
Fuel pump
check the maximum fuel pump pressure
block the return line with special pliers
the pressure should rise above specification
Pressure regulator

24. Low Fuel Pressure Pinch the return line
If the pressure increases above normal, the regulator is probably bad

25. Causes of High Fuel Pressure
Faulty pressure regulator
Blocked return line
check the return line for free flow
if flow is free, the regulator is suspect

26. Pressure Regulator Location

27. Injector Problems A bad injector can cause a wide range of problems:
rough idle
hard starting
poor fuel economy
engine miss
Leaking:
extra fuel drips from closed injector valve
causes rich mixture

28. Injector Wear Dirty: Inoperative injector: Poor spray pattern
restricts fuel flow
causes lean mixture
Inoperative injector:
shorted or open winding
Poor spray pattern

29. Throttle Body Injector Service Wear safety glasses Remove air cleaner
Inspect injector for rapidly pulsing spray pattern with engine cranking or running

30. Check injector supply voltage
TBI Circuit Checks
Check injector supply voltage

31. Measure exact supply voltage
TBI Circuit Checks
Measure exact supply voltage

32. Jump circuit; use ohmmeter at the other end
TBI Circuit Checks
Jump circuit; use ohmmeter at the other end

33. Testing TBI Injectors Follow service manual procedures for diagnosis
Check for power
no power indicates a problem with the wiring harness or the electronic control module
if power is reaching the injector but no fuel sprays out, the injector may be bad
make sure fuel pressure is within specifications before condemning an injector

34. Testing TBI Injectors
Label wires and hoses

35. TBI Injector Replacement
Remove the fuel metering body

36. TBI Injector Replacement
Pull out the old injector

37. TBI Injector Replacement
Use new O-rings and washers

38. TBI Injector Replacement
Align and push the new injector in

39. Servicing EFI Multiport
Injectors
Use a stethoscope to listen for the opening and closing of injector valves
if the injector is not opening and closing, check the resistance of the injector coil
Following service manual procedures for diagnosis, check for power
Check for pulsing ground from the control module (use noid light or oscilloscope)

40. Stethoscope Place a stethoscope on the injector
A clicking sound indicates opening and closing

41. Injector Tester Checks for injector coil problems
Faster and more accurate than a voltmeter or an ohmmeter alone
Sends current through the injector

42. Compare readings #5 is low, replace
Injector Tester
Tester connections
Compare readings #5 is low, replace

43. Noid Lights Special test light for testing EFI circuits
Connect in place of the injector
Crank or start the engine
A flashing noid light verifies power at the injector

44. Noid Light Kit Use the correct noid light to prevent
damage or misdiagnosis

45. Noid Light Use Release locking mechanism and remove connector
Install light and start engine; light should flash

46. Injector Balance Tester

47. Injector Balance Testing
Connect pressure gauge to fuel rail
Bleed air and close valve

48. Injector Balance Testing
Connect injector balance tester to injector terminals and battery

49. Injector Balance Testing
Press tester button to pulse injector
Note pressure drop

50. Injector Balance Testing
Test each injector
The pressure drop should be the same at each injector
The injector with the least drop might be clogged
The injector with excessive drop might be sticking
If pressure does not hold, the injector might be leaking

51. Injector Balance Testing
Remove connections

52. Injector Balance Testing
Connect the equipment and pressurize the system by cranking the engine or cycling the key on

53. Injector Balance Testing
Observe the pressure drops. Cycle the key between each check to pressurize the system.

54. Multiport Injector Removal

55. Multiport Injector Installation
Seals, washers, and boots must be in perfect condition

56. Injector Cleaning Injectors that fail the balance test may be clogged
Deposit buildup may cause poor spray patterns, causing hard starting and poor economy, emissions, and power output

57. Injector Spray Patterns
Good, even, partially atomized
Poor, solid stream
Poor, dirty nozzle
Poor, uneven pattern

58. Injector Cleaning
Shop air is used to force cleaning solution through the injectors to remove deposits
Connect the tool to the fuel rail

59. Engine Sensor Service Throttle position (TP) sensor
Manifold absolute pressure (MAP) sensor
Oxygen (O2) sensor
Engine coolant temperature (ECT) sensor
Intake air temperature (IAT) sensor
Airflow sensor

60. Throttle Position Sensor
Affects fuel mixture, ignition timing, and other outputs
Contact points or variable resistors can wear and fail

61. Throttle Position Sensor
Monitor sensor voltage on scan tool
Probe sensor voltage drop with voltmeter
Measure sensor resistance with ohmmeter
Adjust resistance or voltage to specifications by loosening mounting screws and rotating sensor

62. Manifold Absolute Pressure Sensor
Affects fuel mixture when engine accelerates and decelerates
To test, monitor sensor voltage or resistance while applying specified vacuum levels to the vacuum fitting

63. Oxygen Sensor Sensor operation affects fuel mixture
The sensor may produce a false output
The control module cannot precisely control fuel mixture without an accurate signal
The sensor may wear out or become contaminated

64. Contamination Sources
Leaded fuel additives
Silicone from antifreeze, RTV sealer
Carbon from rich mixtures

65. Black soot from a rich mixture
Reading a Sensor
New sensor
Black soot from a rich mixture

66. Reading a Sensor
Antifreeze contamination
Silicone contamination

67. Reading a Sensor
Lead contamination
Oil contamination

68. Engine Coolant Temperature Sensor
Sensor operation affects fuel mixture and ignition timing
To test, monitor sensor resistance at various temperatures
If test readings are not within specifications, the sensor should be replaced

69. Intake Air Temperature Sensor
May not have a pronounced effect on operation (may trip DTC)
To test, monitor sensor voltage or temperature on a scan tool
Measure sensor resistance at various temperatures with an ohmmeter

70. Airflow Sensor Sensor operation affects driveability and emissions
Sensor may become shorted or opened
To test, check air ducting for air leaks
Monitor sensor voltage on a scan tool
Check sensor voltage drop with a voltmeter
Measure sensor resistance with an ohmmeter

71. Control Module Service
A faulty control module must be replaced
Early systems use a removable programmable read only memory (PROM) chip that can be reused in a new control module
Recent systems use a PROM chip that cannot be removed from the control module

72. EFI Multiport Circuit

73. Gasoline Injection Adjustments
Several tune-up adjustments may be needed:
idle speed adjustment
throttle plate stop adjustment
idle air-fuel mixture adjustment
throttle cable adjustment

74. Adjustments and access locations will vary
Typical Adjustments
Adjustments and access locations will vary

75. Testing Idle Control Motor Affects idle speed
Servo motor may become shorted, open, or may have worn internal parts
IAC motor tester may be used to drive servo motor, verifying its operation

76. IAC Motor Tester Connect the tester to the IAC motor
Use the tester to drive the motor, increasing and decreasing idle speed

77. Multiport Throttle Body
Service
Usually involves replacing dried, deteriorated gaskets and seals
Remove the throttle body from the engine
Disassemble the unit
Inspect parts for wear
Replace worn parts
Reassemble with new gaskets and seals
Reinstall on the engine

78. Replace gaskets and seals; check for throttle shaft wear
Throttle Body Service
Replace gaskets and seals; check for throttle shaft wear