Low voltage to fuel pump
 

A have very limited experience with electrical and had a friend show me how to test voltage. My blazer stopped running a few weeks ago for no obvious reasons. It would try to turn over but would not start. So I tested my fuel pressure i had only 30 lbs. So I dropped the fuel tank and pulled the pump. Just for fun I checked the fuel pressure of the pump out of the tank and had 70 lbs plenty of pressure to run the fuel system. So I checked the voltage and had only 5v at the connection for the pump. I tested the relay for the fuel pump under the hood (it is the same for the window glass and the horn all three of my relays where good). I removed the fuel pump relay and tested the connections I was only getting 8 volts to the fuse block. Intermittently the ignition would act funny the lights would flash on and off but removing the key and trying again would solve the problem. Could it be my ignition or has my computer died... where should I go from here I'm stumped.

Year, make, model, and engine are necessary ;)

I'm going to assume you have a 2000 blazer.
you always start checking voltage at batt terminals themselves.. either posts in standard batt or the terminal bolts for GM sidepost. Normal fully charged voltage is 12.6 after several hours or overnight over 32 degrees.

With ign on headlights off not cranking you should have more than 11.5 v

Also check neg batt terminal to chassis and engine. with headlights on should read less than .25 volt

You could have bad ignition switch causing low volts and those symptoms but it could also be the battery cables and connections.

The main power connection to fuse block do not go thru the ign switch
If you read eight volts anywhere on or near fuse block check the conn where batt cable hooks up at base of fuse block.

Yes It is 2000 blazer 4 door 4 wheel drive. I am getting 12 volts from the battery I'll check out the battery cables and fuse block connection tomorrow. Super fast response thanks.

I rechecked the voltage to the battery I showed 13 volts at the battery and I showed 13 volts at the power cable coming into the fuse block. with the key off i show 13 volts at the fuel pump relay. with the key turned on the voltage dropped to 10 and still no volts at fuel pump. I think the ignition maybe the culprit...any ideas.

The fuel pump relay terminals can be checked by removing the fuel pump relay and carefully probing the terminals in the fuse panel:

Dark green with white trace wire:
From PCM to trigger the fuel pump relay. When the ignition is initially turned to the RUN position, the terminal must show battery voltage for 2 to 3 seconds, commonly referred to as "pump prime". After pump prime, the PCM deactivates the fuel pump relay and voltage should drop to zero.

Black wire:
This is the ground for the relay. It must show less than 5 ohms resistance to ground at all times.

Orange wire:
Comes from ECM B fuse and must show battery voltage at all times.

Grey wire:
Runs from the fuel pump relay to the fuel pump. At the fuel pump module connector, this wire should only show battery voltage during pump prime, (2 to 3 seconds) when the ignition is initially turned to the RUN position.

The "pump prime" terminal on 2000 is in the underhood fuse panel right next to the fuel pump relay. It's a small single female terminal. The terminal wire splices to the grey wire in the fuse panel and goes directly to the fuel pump module. If you apply battery voltage to the terminal, the pump must run. If it does, wiring from the relay to the pump is good. If not, check for an open circuit, or poor ground to the pump.

Thanks for the good info it is appreciated I am going to re check the voltages again at the fuse block the only wire that had any power last time was the Orange wire. I am going to get someone to help me today so I can see if the prime connectors are getting power and I will also check the prime test connection.
Yesterday I tried splicing a hot wire onto the grey wire at the pump connector I thought this would supply constant power to the pump and the pump would run continuosly. however the pump did nothing. Today I will check to make sure the ground wires are making contact. I hate electrical problems !!!!!!

Well everybody thanks for the help. Turns out the low voltage problem was a worn out ground probe on the meter I was using. I did find my problem It is the four way plug to the fuel pump I get power all the way to the plug and I show and I show continuity through the pump. I am just not getting connection from the plug to the prong connections. No wonder the replacement pumps now come with a different style connector I have ordered a new pump and assembly for 60 bucks on e-bay. I hear a lot of bad about these aftermarket pumps hopefully it will last. Oh well now I have a spare pump and a intimate knowledge of the fuel pump and its wiring...lol. I will post on this thread one last time when my new fuel pump is in and my blazer is running thanks again. Blazer forum Rocks!!!

Gee. I have a 'spare' as well. I bet half the fails on here really are those connectors. Especially the ones that go from 'starts easy' to fail on road.
- but like most, I just replaced the pump even though I found it when I got the tank out and the Delphi was still in the bag.

If you'd checked with some supply house you'd probabaly find those 2x2 pigtails available . Rockauto has them. Now the bad part is that if you got about 110,000 that is about the life of the pump far as I can tell.
One thing I do know.. chances are 50% that, if you're honest, you'll be coming back here in less than a year and admitiing you you have listened to 'rumor'.

I'm Finally back up and running with a new fuel pump. this is the second I have purchased if it fails again I'm just gonna replace it with an inline fuel pump. I totally agree with pettyfog I think alot of these fuel pump falures could be the original 2x2 pigtail connectors. I didn't even check the original fuel pump I just tossed it. The second pump (the one I just pulled out) Is an AC Delco and I almost threw it away. The connector was the only problem. I couldn't have figured it out without the help I found here on the forum.