Hello, I am new to this site and I hope someone may have an answer to my problem. My son has a 2001 Extreme Blazer. He was driving it home and it just quit, I checked the relays and fuses and all is well, but there is no power to the pump, I have been told there is a fuel pump oil pressure switch. If so where is it located and what does it look like, 5000 miles ago i rebuilt the heads and changed the fuel injection spider thing, and replaced the oil sender
by the dist. The car is a 5 speed. Is their something i am completely overlooking. Thanks in advance

 

My first question is how did you check the relay?, The horn relay is the same as the fuel pump i just switch them out and beep the horn to see if the relay works. Then did you test the square 4 pin plug color code "black,black/w. stripe,purple,grey" for power at the fuel pump, Or the plug next to it on accident?

 

The gray wire is the hot to the pump, purple is to the sender and blacj is ground.
The oil pressure sender that you replaced is the "fuel pump oil pressure switch" so you are familiar with where that is. The orange wire that goes to it is the hot in and the gray wire goes to the pump. The sender is actually dual purpose. With a loss of oil pressure it will stop the pump like if you got in an accident and the engine stopped, it would shut off the fuel. Safety factor.

 

Okay, i think you hit on something. while checking the sending unit, i noticed
only the orange wire. i did not see the grey wire on the connector. It may have broken off. I did check both connectors at the tank and neither had any power. did the same with the relay as you did and they are fine as well. I will look at the sending unit plug Thanks

 

The purple wire at the tank runs through the fuel gauge not the oil pressure switch, This is the sender unit "hot" wire. I thought you only had one connector at the tank that the pump, sender and ground run through. With the key on you should get 12 volts out of the purple wire. I would check the grounds real good at the tank. They probably ground at the frame aft of the tank. Make sure they're clean.

 

No luck. i have no power to the wires. Is there a fuseable link somewhere between the fuse box and the pump? the ground was cleaned and it still made no change.

 

Your sender probably runs off your Ignition/Gauge fuse through the gauge and the pump probably runs off the ECM B fuse. I don't have a wiring diagram for your truck but most of these are the same. If anyone else has a W/D for this jump in. If you don't have power to either one of them and they run off two different circuits something they share has to be the problem. I would suspect
1) A faulty connector
2) Cut or damaged wiring
3) Ground wire open
It's probably a good idea to get the meter out and start checking for blown fuses, shorts to grounds and opens in nthe wiring. Have you tried the prime port? Best idea they put on these things. This would tell you of the wire directly to the pump is good (if the pimp runs) or bad (if it doesn't).

 

where is the fuel pump test port and what does it look like

 

It's a wire coming out of the loom near the junction block on the right side of the firewall. It's probably a gray wire but some are tan. It is the only wire with a single connector not connected to anything. Sometimes you really have to look for it. It's there. You need to put a FUSED jumper from the battery to it. I used an in-line fuse holder with an extension. The extension has a single male blade terminal end on it. The other end of the jumper (fuse holder) has an alligator clip to attach to the battery. To join the two the choice is yours. I made mine with blade terminals so I could use it in other applications. You need a 15 amp fuse in it. DO NOT OMIT THE FUSE HOLDER. Then you just connect one end to the wire and the other end to the battery + and it'll run your pump all day or until the battery dies. I used 14 gauge wire on mine but 12 would probably be better. Of your pump still doesn't run at least that will give you a chance to see if you have voltage back to it. I take it your gas gauge doesn't work either. This won't help you there.

 

Edd
Any luck?