This vehicle has an intermittent misfire that we are trying to locate. Here we will be focusing on the injectors, making sure they do not have any flow problems (restrictions or leaks) An external timer tool will be used to fire the injectors at exact intervals while watching fuel pressure drops on a pressure gauge. Since we cannot get to the injector connectors directly, we will be using a main bulk connector to access the injector control wires. This same procedure can be applied to many different systems.

Engine Performance Diagnostics chapter 16 pages 9-16

symptoms 50

  • fuel pump fuse keeps blowing
  • intermittent no start
  • fuel pump relay buzzes
  • when heater is turned on the fuel pump relay fuse blows

fix 50

  • repair loose main block ground

test shown enh 50

  • fuel pump current measurement using a low amp probe and scope
  • GM fuel pump relay diagram breakdown
  • fuel pressure test
  • fuel pump relay control circuit test
  • fuel pump relay ground test
  • fuel pump relay load side test

Tools used

  • lab scope
  • low amp probe
  • wire piercing probe
  • jumper wires
  • back-probing pins

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(Chapters 14, 15,16) Fuel Delivery and Fuel Pressure Testing

Related videos:

Low Fuel Pressure from a bad fuel pump ground (Ford Ranger):


Poor running, flashing CEL, no codes (bad computer ground) Toyota:


Fuel pump electrical circuit diagnosis (no fuel pressure testing) GM:


How to test an electric fuel pump (no fuel psi testing) Ford:


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


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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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