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New Fuel Pump Question

xzz0195

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xzz0195 Enthusiast

xzz0195

Posted
Posted

Into my third day of fuel pump replacement and am having some trouble. The part I purchased from NAPA was a Delphi FG0053-02 per discussion with them. It has a new harness type which required me to cut the wires and put on new harness. Not hard to do because the colors all matched on old wires and new harness. Lifted the tank and tried to start. No go...

 

So I dropped the tank and started to test electrical first. Had 100% continuity from cut wire(s) location to new harness on all 4 wires. This told me that the splice job was good. Next I tested voltage and saw in AUX position the 5 volts for computer modules and then saw (when cranking) 8 volts between (gray and ground). Thought it should have been 12 but I did read 8 volts. I tested this multiple times with same results.

 

Next I pulled the Gas Line on the Pump marked "F" fuel to the engine. Tipped tank back up level and cranked for a while, no gas came out of the "F" side of fuel pump.

 

I am thinking I have a brand new pump that doesn't work... Thoughts?

98 Z71 SLT Senior Enthusiast

98 Z71 SLT

Posted
Posted

Grey wire, should be at 12v with key -on- or -start-

 

8volts means you have a voltage drop somewhere

 

I'd suspect the new connector you installed

 

If the new connector is ok, replace your fuel pump relay, in underhood fuse block

xzz0195 Enthusiast

xzz0195

Posted
  • Author
Posted
Grey wire, should be at 12v with key -on- or -start-

 

8volts means you have a voltage drop somewhere

 

I'd suspect the new connector you installed

 

If the new connector is ok, replace your fuel pump relay, in underhood fuse block

 

 

Actually, I tried the relay theroy today by swapping an existing relay (same exact type from another slot) The electrical testing I did was after the fuel pump relay switch. So I'll work on finding the Voltage drop tomorrow. But I was thinking if I have close to 0 ohms from the splice to the relay, there can't be a drop there, it's starting to look like it's forward from the cut wires. According to other posts on this site low voltage can be root cause for pump failures.

xzz0195 Enthusiast

xzz0195

Posted
  • Author
Posted

Given: Delphi FG0053-2 New Fuel pump installed won't pump gas.

 

Figured out root cause of voltage drop last night. When I removed the tank, I had disconnected the ground wire that attaches to the back side of the fuel door. Unbeknowst to me there was another wire, behind that wire that I did not see. That other wire WAS the ground to the fuel pump. So the 4 volt drop I was reading was the voltage drop across the pump itself because the ground side was open....

 

Learned a couple of other things.

 

Gray------+ Fuel Pump Should read 10 to 12 volts

Black----- - Fuel Pump

 

Purple ----+ Only 5 volts -- These go to the sensor

Orange --- - Is ground

 

I believe the Purple and Orange are the fuel guage wires.

 

Test procedure before raising tank...

Simply have someone start the truck with fuel side line disconnected at fuel pump, as soon as key goes to AUX or the engine is cranked gas will flow from pump. Do this before raising tank. If it doesn't work then you have an electrical issue.

 

There are four wires coming into pump. You will have most likely put in new harness which requires you to cut and splice all four wires for new connector. Make sure to attach ground wire before testing...obviously....

 

Fuel Pump -----Gray ------------+1--Splice----+2-----------> Engine side

Fuel Pump -----Black ------------+1--Splice----+2-----------> Truck Ground which is really anywhere

 

Because the other two wires have nothing to do with fuel pump, you don't have to test them.

 

With Volt meter on DC (20 Volts full scale setting), put key in aux. Place red lead to +1 and black to +2 you should read 10 to 12 volts. Place leads at +2 for next test, same reading should be found.

 

If you read only 6 or 7 volts, then you have a bad ground. Make sure to reset the ground wire from fuel door to truck body side. If you can't get the voltage up, take a new reading by attaching to +1 and then to any point on truck body. If you see voltage increase you have a ground issue. A simple fix is to attach a new ground wire to Splice point +2 on Black wire and run directly to the closest point on truck. You can use a self-taping screw and drill a small hole into body slightly less diameter than screw. Place a rounded electrical connector on the side that connects to body. (Should solder it in, in addition to crimping). Attach to body side. Retake reading and your voltage should read 10 to 12 volts. Recheck pump discharge before lifting tank.

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