I have lost power to my fuel pump. Im getting the 5 volts from the computer to close the fuel pump relay but I don't have the 12 volts that is switched .Ive looked at the limited diagram Chiltons has but cant find it. Any one know where the 12 v. comes from?
Steve

 

did you change the relay? Checked for voltage back at the pump plug?

 

Yes new relay and no power at fuel pump plug.What I need to know is where does the realy get its switched 12 Volts.
Steve

 

i had a similar problem on my '92 Jimmy.

i just ran a SPST switch inside, that ran a jumper wire from the large orange wire that comes into the relay (constant power) to the one for the fuel pump.

this was after i had replaced the underhood wiring harness i had kicking around (which i had to rewire 'cause it was for an automatic), and did nothing to solve my problem.

just be sure to install a litlle LED (or some kind of lighted switch) so that you never forget to turn off the pump, for 3 1/2 hours, leaving you stranded @ the side of the road, @ 3am!

***edit*** didn't you also have an issue with your 4-ways and the injectors on this thing a little while ago, too? did that issue get resolved? maybe the two are related????

 

According to my Chilton manual and wiring diagram the pump gets power from the ECM B fuse. This supplies voltage to the relay and oil pressure sender through the Orange wire. You might want to use the fuel pump prime port to see if your pump is bad. It's the Tan/White striped wire on the right side of your firewall adjacent to the junction block. It's has a single female connector on it that isn't attached to anything. You can run a FUSED jumper straight from the battery to it and you should hear the pump run. Make the jumper out of an in-line fuse holder with terminal ends crimped on. I put an alligator clip on one end to make the battery hookup easier and a male blade terminal end on the other side to hook to the wire. Use a 10 or 15 amp fuse. This bypasses everything and goes right to the pump wiring.

 

swells244
Any luck with the fuel pump? A little more info to really answer your question about power to the F/P relay. You will see a Dark Green/White Stripe wire on the relay. This is a power wire that comes off your PCM (or ECM or ECU - whatever) and energizes the relay on start for about 2 seconds. The Orange wire is the actual power wire that passes through the relay to run the pump. The Black/White wire is ground for the Dk Grn/Wht wire and the Gray wire goes to your pump. Didn't know if my previous post answered your question but if it didn't this should.

 

I haven't had a chance to check it yet.Ill have time tomorrow .Ill post what I find.

 

Ok finally got it running.ECMb fuse was blown .I replaced the fuse and it blew again.The pump really had a loud grinding sound.So I pulled the tank and replaced the pump and the fuel filter(which is in a really ugly spot).Tried to start the truck which didnt happen.Ok lets see what the fuel pressure is guage reads 0 , What the heck!!So I take the fuel line off behind the left rear wheel where it goes to the tank , turn switch on fuel squirts every where.So I get a cold glass of ice tea and set under my shade tree and contemplate the meaning of life and Blazers.I get under the truck and am checking the metal fuel line for kinks or any thing out of the ordenary .Whats that another fuel filter.Some one had cut the line and installed a filter in line that is completely stopped up.
Any way runs good now!!
Steve

 

Glad you got it fixed! Thanks for the follow up!

 

X2 on getting her back on the road again.

don't you just love when *ahem* "people" that shouldn't be under the hood-let alone under the truck-try to "fix" something. @ least it was a relatively easy solution.