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Fuel pump refuses to work

I have been struggling to make this thing work. We have replaced the fuel pump with brand new ones twice now, replaced the FP relay, tested the voltage, ohms, and amperage under load and with out, and have tested the pump directly hooked to the battery and it works. For the life of me I can’t figure out what is going on. Any help would be appreciated

How can anyone help if we don’t know the year of this Blazer?

Tester

It’s an 02, sorry. I forgot to put that in the info.

Let’s be absolutely clear on something

2002 Chevy Blazer 4.3 V6 . . . ?!

or is it a 2002 Chevy TrailBlazer 4.2 inline 6 . . . ?!

I’m asking because some people use the word Blazer, when in fact they meant Trailblazer

it sounds like the pump isn’t getting a signal to energize . . .

It’s a Blazer 4.3 v6. As far as I know it is getting power. A buddy just told me to try and run a new ground, worth a shot after doing everything else

The powertrain control module controls the function of the fuel pump relay.

Tester

The pcm is good, I get power to the connector at the pump but under a load it’s no good.

Exactly what does that mean?

Does it mean you’ve verified . . . for example with a 12V test light and/or digital multimeter . . . that the fuel pump is getting power?

Or does it mean you assume the pump is getting power?

We verified with a multimeter and test light

Sounds like you’re going to have use a multimeter to find out where the voltage drop is

Could be bad connections at an intermediate connector, fuel pump relay contacts, etc.

I wouldn’t at all be surprised if the bad connection . . . burnt brittle, for example . . . is inside the fuse box itself. I’ve seen this a few times

I’ll hunt around for something like that, hopefully it’s not too deep in there. I just talked with some one and they said it could potentially be the ground from the ignition, does that seem like a possibility?

I’d be looking at ground G402 as shown in the wiring diagram.

Tester

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I cut the ground and wired it to a bolt on the frame and… She Runs! Now to just put it all back together.

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I believe that all you have proved is that the ground is not being established when it should have been. You need to find out why that is. Otherwise, your pump will not be disconnected from ground when it should. (Is the ground controlled by computer? (“Tester” obviously understands this better than I do.)

That’s what the relay is for. It doesn’t send the power unless it’s asked for. Where it’s grounded shouldn’t matter.

I suspect the problem with the ground connection is in the splice pack SP423 as shown in the drawing. Bad connections can seem to be okay until a good load is placed on the line. Using a meter or test light to check for power can fool you at times since they don’t require much current to make them operate. Using something a brake light or head light would help show up a bad connection since they require more current to run them. Like you say, the ground side of the circuit is tied to ground at all times. The FP relay controls the ‘hot’ or power side of the circuit in order to turn the pump on or off.