1999 Chevrolet Blazer No power to fuel pump

Tiny
JOHNNYSILVERWOLF
  • MEMBER
  • 1999 CHEVROLET BLAZER
  • 4.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 165,000 MILES
Driving then it quits like it ran out off Gass gauge says half tank checked pressure got none checked fuses good
Had no noise from fuel pump so I pulled and check pump, pump is good checked pump wires for power got none recheck fuel pump relay under hood checked elm fuse a and b good what other relays and fuses can I be missing? Can you help
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Monday, June 15th, 2015 AT 9:34 PM

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Tiny
CARADIODOC
  • EXPERT
Have you checked for spark?

Under what conditions are you expecting the fuel pump to have voltage? Do you have the ignition switch on? Are you cranking the engine?
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Monday, June 15th, 2015 AT 9:43 PM
Tiny
JOHNNYSILVERWOLF
  • MEMBER
I have the key on and tried cranking still no power to pump
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Tuesday, June 16th, 2015 AT 6:53 AM
Tiny
CARADIODOC
  • EXPERT
Dandy. The engine has to be rotating to have voltage going to the fuel pump. To run otherwise would pose a serious fire hazard if a fuel line got ruptured in a crash.

Have you checked for spark?

A failure in the ignition system is responsible for about one percent of "cranks / no-starts". A failure of the fuel pump is responsible for about another four percent of those no-starts. It's a loss of fuel pressure AND spark that account for the majority of the no-starts, but too many people get hung up on the first thing they find missing, and they don't check for other clues and symptoms.
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Tuesday, June 16th, 2015 AT 2:14 PM
Tiny
JOHNNYSILVERWOLF
  • MEMBER
Yes motor will start with starting fluid or gas until it burns out have used jumper wire from battery to pump relay and got power to fuel pump connector that way but when jumper is pulled no power when ING switch on and off no power when cranking no power so I know the wire between fuse block and pump connector is good I know motor will crank and run know fuel pump will run just don't know why when connected right fuel pump has no power can the oil pressure switch or oil pressure relay under distributor cause this problem if gone out?
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Tuesday, June 16th, 2015 AT 2:47 PM
Tiny
CARADIODOC
  • EXPERT
Before I forget, there is a common problem you should be aware of if you have a steel gas tank. The pump is grounded through it to the straps, then to the frame. If the tank gets rusty, that ground can be lost. You'll have that 12 volts on the feed wire, but a faster way to check for this problem is to use a simple test light. Ground it to a good, paint and rust-free point on the body, then place the probe right on the tank. If the test light turns on dimly, drill a small hole in the tank's flange, outside of the weld, then run a screw in there and attach a wire to it and to the frame.

At the pump's connector, you should have been testing on the gray wire for 12 volts. You should normally see 12 volts for one or two seconds after turning on the ignition switch, then again when you're cranking the engine. If you DO see 12 volts for the first couple of seconds, we know the relay and wiring are okay, and the Engine Computer has control of that relay.

If you don't see that initial 12 volts, we're going to have to test at the relay. Either you're going to have to gain access to the underside of the fuse / relay block, or you must find a way to test on the relay's terminals while it's still plugged in. You might be able to lift the relay just enough so you can poke the test light's probe in there, or you can insert little pieces of wire to use as test points. You have to be careful though to not put enough pressure on the terminals in the socket that they become stretched. That will cause them to make intermittent contact.

To start with, you can remove the relay completely, then test at each terminal with the test light. There should be one with 12 volts all the time. If you're doing this underneath, that will be on the orange wire.

Next, move the test light's ground clip to the battery's positive post so we can test for grounds. Probe the remaining three terminals in the relay socket. One will make a bright test light. That's the ground wire for the relay and is black. Now look for a second terminal like that. That is a green / white wire. The test light should light up but it will be relatively dim because you're also reading to ground through the pump motor.

If those three circuits are okay, we have to determine why the computer isn't turning the relay on.
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Tuesday, June 16th, 2015 AT 5:08 PM

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