Hello.
Really need help now.
Replaced fuel pump now for the third time, but the new one will not start, get power right up to the pump for a few seconds as it should, but there is no life in the pump.
Tried to connect power directly to the pump we just took out and it worked.
What can it be then?
It's a 1999 4.3 liter.
And we bought ACDelco to be on the safe side.

 

So you have power at the pump connector but the pump does not run?

George

 

Hello George

Yes, have 12.4 volts at the plug and then I measure both ground and positive in the plug. What is strange is that the old pump worked when we connected it straight to power after we had taken it out, but since we have heard so much negative about parts that are not ACDelco we chose to replace the old one anyway.
Per

 

Did you solder the new connector and how are you checking ground?

George

 

The new plug was already mounted earlier in the workshop when they replaced the first pump.
I only checked that it is ground and positive in the connector and there I got over 12 volts out on the multimeter.
Have read that there are some problems with splice pack 423, but tomorrow I will try to connect the old pump directly to the connector to see if it works the way it did when I connected it to the battery.

Per

 

You have to make sure that you have a good clean ground to the frame and no wiring issues. Both 12V and ground must remain in good shape under a load. Corroded or poor connections can read OK as open but fail under maximum current draw. Check the resistance from the ground at the pump to a clean spot on the frame. Then measure the net voltage across the ground and power as close to the pump as possible under a load.

George

 

Today I tried to connect the old pump straight to the connector, but it didn't work. Checked again right on the battery and then it worked.
Cut off the 2 wires grounded in point G402 and made a new grounding point and also mounted a new cable straight to the ground of the pump, but still dead.
Have to use the multimeter to search further or add a new positive to the pump from the fuse box.
Could there be something wrong with splice pack 423?

Per

 

The pump is only energized by the fuel pump relay control signal for a few seconds when you first turn the ignition key on. For constant power on that fuel pump power line use the prime connector at the fuse block and verify voltage at the pump connector. Once you have proven constant power at the pump connector supply a good ground to the pump with a jumper wire to the frame. I see that ground splice pack now so the ground is not just a straight shot to the frame. Did you measure continuity from the pump ground to the frame to see if there is a ground wiring/splice issue?

George

 

We have equal 12 volts both on the prime connector in the fuse box and on the plug of the pump as it should be for about two seconds when we turn on the ignition.
I also took a wire straight from the battery to the ground point on the frame without making any difference.
That's why I'm thinking about adding new wires from the engine compartment and back to the pump.
The fuel gauge works the way it should .

 

Your truck does not have G402 for the pump, that looks like a full size pick up thing. Assuming Blazer, your pump ground goes through S423 first then on to the frame at G416. What I dont understand is the wiring diagram shows S422/423 by the dash and G416 at the left rear frame which means the ground makes a long round trip. The labels might be wrong. For the S10 the ground is a straight shot to the frame at G416.

George