Honda PGM-FI Main Relay Testing (1998 Honda Prelude) How to test and fix a main relay on a Honda or Acura.

Engine Performance Diagnostics chapter 18

symptoms 50

  • no start with good spark, fuel and compression
  • start/stall
  • stalls and will not restart for a period of time

fix 50

  • replaced PGM-Fi main relay fuse

test shown enh 50

  • how to determine what is powered by the main relay
  • main relay wiring diagram review
  • how to identify condition of the main relay by testing for power at the fuel injectors and idle speed control motor
  • how to test a PGM-FI main relay
  • how to locate the main relay
  • how to remove the main relay
  • how to locate a cracked solder joint on a circuit board

Tools used

  • incandescent test light
  • soldering gun

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(Chapters 17, 18 and 19) Fuel Injector Testing

Related videos:

Operation and testing of a Honda main relay (PGM-FI) - an SD Premium video:


How to identify a bad main relay on a Honda (PGM-FI):


How to test fuel pressure, injector pulse and spark with basic tools:


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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available as an eBook or paper book.

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