Raymond Chen Posted January 5, 2008 Share Posted January 5, 2008 I currently have a 1991 Lexus LS400 that will not start, even though it cranks. I have narrowed down the problems to be fuel system related, and I have already removed the fuel pump from the portal behind the rear seats. When I attached a multimeter to the terminals on the fuel pump, and turned the key to crank the motor, I found that I am not getting the full 12 volts as I should, but instead, I am getting only 4 volts. Can someone please tell me what would cause this? Quote Link to comment Share on other sites More sharing options...
steve2006 Posted January 6, 2008 Share Posted January 6, 2008 The fuel pump supply is controlled by the fuel pump relay and has 2 outputs. One supplies the fuel pump under cranking conditions and the other supplies it during engine running mode but is via a ballast resistor. I would 1st check the supply voltage with the ignition on but not cranking the engine. As you are getting some supply to the pump I would go for the fuel pump relay 1st ( easy to change, passenger side fuse/relay block) then check the ballast resistor. Quote Link to comment Share on other sites More sharing options...
SKperformance Posted January 6, 2008 Share Posted January 6, 2008 I would look at the relay it sounds like it is corroded. Quote Link to comment Share on other sites More sharing options...
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