Chevrolet Repair: fuel pump power, chevy blazer, evaporative emissions

Question
QUESTION: 1997 chevy blazer 4wd s10 4.3 vortec v6 .....I took it to a garage and was told it was not getting enough  fuel pressure that pump was bad ,replaced pump and when turned key pump did not kick on started looking at fuses and wires and had one rare occasion when power kicked on and pump ran for few seconds then nothing again. my question is should i test the wiring from the ignition to the pump ? and what does the sensor on top of pump do if its wiring is messed up could it be telling the computer not to send power to the pump thank you for any help

ANSWER: Hey,

  The sensor on top of the sending unit is for the EVAPorative emissions.  It checks the pressure of the tank and has nothing to do with fuel pressure.
  The pump does not run all of the time unless the motor is running.  Wehn you turn the key the pump gets a 2 second prime cycle.  I would try removing the relay and jumping the switch section of the relay (the relay diagram is printed in white on the side of the relay).  There is a coil and switch section.  The coil is the control from the PCM and the switch is basically 12 on one side and fuel pump on the other.  IFyou jump this relay with a paperclip check for 12v and ground down by the pump.  If that is good and you still don't have fuel pressure you have a defective pump.

Wayne


---------- FOLLOW-UP ----------

QUESTION: ok jumped across and have power so i went and bought a new relay put it in and again have nothing. gentleman at part store said to look at ecm if relay did not help .Can you give me insight into what to look at on ecm or do you think there is something else wrong?

Answer
Hey,

  Ok,  when you are cranking it take a look at the two terminals that are indicated as a coil on the relay.  Once should have 12 all of the time and the other should be a ground when the vehicle is cranking.  tests this with a meter not a test light because the computer controls the ground.

WAyne