I have 02 envoy, ihave changed the fuel pump i have tried relay but after I changed the pump I then discovered that there's no power getting to the fuel pump relay i have had this problem in the past

Fuse or loose wiring?

There is not a reset switch on a Envoy. If your pump is not running check the fuse and the relay. If you are getting power to the relay and the relay is operating, it is time to drop the tank.

The alternator isn't charging , battery drained . Is the battery symbol lit on the instrument cluster ? What guy said something about low voltage ?

Under the hood in the fuse and relay center. The location of components is on the underside of the boxes lid.

Check to see if you have a fuel pressure sensor in the fuel manifold . It is there to stop the pump working when the pressure in the manifold is held constant . IT sends to the ECM which in turn activates the pump relay and turns the pump on.

The pump relay should have four terminals. Number 2 is a green red wire which powers the pump from a 10 amp fuse. Number 3 goes to the pump. Number 1 powers the magnet in the relay and number 4 is the ground signal from the engine computer. If the relay does not engage on its own, one of these circuits is not working.
The injectors get power from that 15amp fuse which gets power from the main relay.
The problem could be farther upstream with the 25amp main fuse.

It can be low fuel pressure or clogged fuel filter or worn out fuel pump.

Check the help links mentioned below to troubleshoot the isue:----

FUEL SYSTEM PROBLEM

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Fuel pump relay and cooling fan relay troubleshooting on 1997 ford thunderbird?

http://repairhelpcenter.blogspot.com/2011/10/fuel-pump-relay-and-cooling-fan-relay.html

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How to Replace a Fuel Injector

http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-fuel-injector.html

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How to Replace a Fuel Pressure Regulator?

http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-fuel-pressure-regulator.html

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How to Replace a Fuel Pump?

http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-fuel-pump.html

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HOW TO CLEAN A FUEL SYSTEM

http://schematicsdiagram.blogspot.com/2011/07/how-to-clean-fuel-system.html

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HOW TO REPLACE A FUEL TANK

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-fuel-tank.html
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HOW TO REPLACE A FUEL TANK CAP

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-fuel-tank-cap.html

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HOW TO REPLACE A FUEL PUMP ASSEMBLY

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-fuel-pump-assembly.html

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Jaguar Fuel Pump

http://schematicsdiagram.blogspot.in/2012/07/jaguar-fuel-pump.html

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Fuel leaks from fuel pulsation dampener on Toyota Corolla?

http://repairhelpcenter.blogspot.com/2012/01/fuel-leaks-from-fuel-pulsation-dampener.html

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Car will not allow to put fuel?

http://repairhelpcenter.blogspot.com/2012/01/car-will-not-allow-to-put-fuel.html

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Adding performance chip to increase Fuel mileage MPG?

http://technoanswers.blogspot.com/2012/01/adding-performance-chip-to-increase.html

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How to test Electric fuel pump on GMC sonoma?

http://technoanswers.blogspot.com/2012/01/how-to-test-electric-fuel-pump-on-gmc.html

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Fuel gauge drops to Empty?

http://technoanswers.blogspot.com/2012/01/fuel-gauge-drops-to-empty.html

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Fuel pump not working on 1991 Ford Ranger?

http://technoanswers.blogspot.in/2012/01/fuel-pump-not-working-on-1991-ford.html

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Fuel pump has no power on 2002 ford 350 7.3 diesel?

http://technoanswers.blogspot.in/2012/01/fuel-pump-has-no-power-on-2002-ford-350.html

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Pushing on the gas pedal, but the car slows down? Gas pedal to the floor and the car slows down?

http://technoanswers.blogspot.in/2012/02/pushing-on-gas-pedal-but-car-slows-down.html

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Ford Fuel pump Relay and fuse location diagram?

http://technoanswers.blogspot.in/2012/02/ford-fuel-pump-relay-and-fuse-location.html

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Ford inside fuse box diagram showing fuel pump relay?

http://technoanswers.blogspot.in/2012/02/ford-inside-fuse-box-diagram-showing.html

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Ford fuel pump fuse layout diagram?

http://technoanswers.blogspot.in/2012/02/ford-fuel-pump-fuse-layout-diagram.html

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How to lower fuel pressure on Toyota Hilux?

http://schematicsdiagram.blogspot.in/2012/02/how-to-lower-fuel-pressure-on-toyota.html

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Fuel pump not running?

http://schematicsdiagram.blogspot.in/2012/02/fuel-pump-not-running.html

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How to replace fuel filter on BMW 525i?

http://schematicsdiagram.blogspot.in/2012/03/how-to-replace-fuel-filter-on-bmw-525i.html

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How to change fuel injector on 2005 gmc envoy?

http://schematicsdiagram.blogspot.in/2012/03/how-to-change-fuel-injector-on-2005-gmc.html

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Time to replace Fuel pump on 1998 Ford Explorer?

http://schematicsdiagram.blogspot.com/2011/12/time-to-replace-fuel-pump-on-1998-ford.html

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Emergency fuel shut switch on Ford car?

http://schematicsdiagram.blogspot.com/2011/12/emergency-fuel-shut-switch-on-ford-car.html

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How to jump fuel pump On Chevrolet Silverado 1500?

http://schematicsdiagram.blogspot.com/2011/12/how-to-jump-fuel-pump-on-chevrolet.html

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How to Increase gas mileage on 2011 2500HD Duramax 6.6?

http://schematicsdiagram.blogspot.com/2011/12/how-to-increase-gas-mileage-on-2011.html

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How to Test and Replace Fuel Injectors on Acura Car Models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-and-replace-fuel-injectors.html

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How to replace Fuel Tank Assembly?

http://vwrepairhelp.blogspot.com/2011/11/how-to-replace-fuel-tank-assembly.html

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FUEL LINES AND FITTINGS on Acura Car Models?

http://repairhelpcenter.blogspot.com/2011/11/fuel-lines-and-fittings-on-acura-car.html

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Replacing Fuel Charging Assembly on Car?

http://vwrepairhelp.blogspot.com/2011/11/replacing-fuel-charging-assembly-on-car.html

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How to replace Fuel Pressure Regulator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-fuel-pressure-regulator.html

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How to test Fuel Pressure and replace Fuel Pump on Acura Car models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-fuel-pressure-and-replace.html

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Car will not take fuel into the fuel tank?

http://repairhelpcenter.blogspot.com/2012/01/car-will-not-take-fuel-into-fuel-tank.html

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PGM-FI Main Relay on Acura Car models?

http://repairhelpcenter.blogspot.com/2011/11/pgm-fi-main-relay-on-acura-car-models.html

2003 Pontiac Grand Prix: Erratic Fuel Gauge?

http://technoanswers.blogspot.in/2012/06/2003-pontiac-grand-prix-erratic-fuel.html

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Fuel Running Lean

http://technoanswers.blogspot.com/2012/10/fuel-running-lean.html

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ECM misfueling Engine?

http://technoanswers.blogspot.in/2012/03/ecm-misfueling-engine.html

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After getting car washed, check engine light is ON and key less entry not working, tried reprogramming. Also car shows fuel pressure?

http://schematicsdiagram.blogspot.com/2011/12/after-getting-car-washedcheck-engine.html

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How to relieve fuel pressure?

http://technoanswers.blogspot.com/2012/01/how-to-relieve-fuel-pressure.html

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Refueling problem?

http://repairhelpcenter.blogspot.com/2012/01/refueling-problem.html

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Toyota Tercel consuming more fuel?

http://repairhelpcenter.blogspot.com/2012/01/toyota-tercel-consuming-more-fuel.html

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How to maximize fuel economy on your vehicle?

http://schematicsdiagram.blogspot.com/2011/11/how-to-maximize-fuel-economy-on-your.html

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Fuel gauge jumps from empty to full?

http://schematicsdiagram.blogspot.com/2011/12/fuel-gauge-jumps-from-empty-to-full.html

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Gas gauge stuck on empty on 2002 Mercedes Benz 240c?

http://repairhelpcenter.blogspot.in/2012/02/gas-gauge-stuck-on-empty-on-2002.html

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No power to the control side of the fuel pump relay?

http://schematicsdiagram.blogspot.com/2011/12/no-power-to-control-side-of-fuel-pump.html

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Fuel Injection Problem And RPM suddenly increases

http://whatisbyme.blogspot.in/2012/07/fuel-injection-problem-and-rpm-suddenly.html

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VAN emits whitish bluish smoke and bad fuel smell from exhaust

http://schematicsdiagram.blogspot.com/2011/12/van-emits-whitish-bluish-smoke-and-bad.html

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Ford runs lean and idles rough?

http://technoanswers.blogspot.in/2012/02/ford-runs-lean-and-idles-rough.html

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Chevy Fuel pressure Reliving Procedure

http://schematicsdiagram.blogspot.com/2012/11/chevy-fuel-pressure.html

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Fuel pressure and spark is good but ford escort will not start?

http://technoanswers.blogspot.in/2012/01/fuel-pressure-and-spark-is-good-but.html

2005 Lexus SC430: Fuel Door will not open?

http://howtobyme.blogspot.in/2012/05/2005-lexus-sc430-fuel-door-will-not.html

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2005 Lexus SC430: Fuel Door, Dome light and Fuel Gauge Fuse Location?

http://howtobyme.blogspot.in/2012/05/2005-lexus-sc430-fuel-door-will-not.html

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1999 Chrysler Cirrus: 8 IGN Fuel Starter Fuse Blows?

http://whatisbyme.blogspot.in/2012/06/1999-chrysler-cirrus-8-ign-fuel-starter.html

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Dodge Dakota stalls, stumbles at idle. Has low fuel flow and runs hot?

http://schematicsdiagram.blogspot.in/2012/03/dodge-dakota-stallsstumbles-at-idlehas.html

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Toyota Fuel line diagram

http://technoanswers.blogspot.com/2012/12/toyota-fuel-line-diagram.html

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These will help.

Thanks.

change the polarity and try

You say you have power at the relay, but what part of the relay? If you don't have 12V at the gray wire going to the pump, then maybe the relay is bad. Also check to see what voltage you have on the dark green/white wire, this controls the relay (should be 12V).

relay