Low Voltage at fuel pump harness

Discussion in 'GM Electrical Tech' started by alchemist1, Oct 18, 2009.

  1. alchemist1

    alchemist1 Member

    I just pulled my fuel tank on the 98 Chevy Suburban and before replacing the pump/sender, thought I would test voltage at the harness connection on top of tank. I am getting about 5.5 Volts (and pressure at Shrader had been about 20psi). At the C103 connector underhood (coming from Fuel pump relay, the gray wire), it is showing full 12+ Volts. Ground is good, as there was no difference in voltage observed between the fuel pump ground strap or running a ground all the way to battery negative.

    Could something have gotten weird with the gray fuel pump power wire running from C103 connector all the way back to the tank??
  2. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Most replacment pumps come with a replacement wiring harness for the truck side of the fuel pump harness because the wiring goes bad over the years. It's possible that's what you are seeing.
  3. alchemist1

    alchemist1 Member

    Call me stupid (idotic). I was probing across the wrong terminal. Did the correct 4 pin terminal and probed across B and C terminals (grey pump power and black ground) and saw 12+V. So pump is likely bad. But here's what I did (another stupid, but couldn't be helped):

    The design of the sending unit fuel connections don't allow the classic scissor style fuel disconnect tool to be used (I have a good quality Lisle one). I had to go get some of the plastic ones at Advance this morning, the 3/8 and 5/16. Anyway, the thing just about won't go into slot because of the design of the connections, but I got it. I pulled the return line away from the sending unit, and I found that the internal spring steel ears had gotten mangled in the process. Basically, the steel spring release thing was still latched around the slot on the sending unit. I'm pretty sure you can't buy those things separately, they look like they should be made into the line.

    couple questions:

    1. Presume I probably need a new return line (up to the union fitting on the frame, midway up the truck)?

    2. Can you insert the steel clamping ears back into the line (doubt it)?

    3. I think someone had done this job before me - the words Airtex were written across the sender and pretty sure he had fubard the steel ears before me?

    Thanks for the help
  4. rogerdsul

    rogerdsul New Member

    Hey, man I got the same trouble on my 2000 silverado, what is up with this stuff..chevy ought to fix stuff like this for free...I checked volts on the harness at fuel pump and am only getting 5.V this seems to be a common thing, I can't tell you any thing about how to fix it, just wanted to let you know your not the only one with this nightmare...

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