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Scott K
Scott K, ASE Master Tech/Instructor
Category: Chevy
Satisfied Customers: 1569
Experience:  20 yrs Experience; GM factory Training ASE Master Certified with L1 advanced engine diagnostics
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1998 Chevy Blazer: no fuel Pressure

Customer Question

1998 Chevy Blazer has no fuel Pressure. has new fuel pump. replaced crank position sensor. fuel pump works when connected direct. but nothing when turns key won't start. tried new fuel pressure sensor
Submitted: 8 years ago.
Category: Chevy
Expert:  Scott K replied 8 years ago.

Hello and welcome to Just answer,


Below is a schematic for the fuel pump circuit for your blazer, first checks are ECM B fuse in the underhood fuse block for voltage both sides and fuel pump relay for click on an ignition cycle from off to run.


When the ignition switch is turned ON, the VCM turns the in-tank fuel pump ON. The in-tank fuel pump remains ON as long as the engine is cranking or running and the VCM is receiving the distributor reference pulses. If there are no reference pulses, the VCM shuts the fuel pump OFF within 2 seconds after the ignition was turned ON or if the engine stops. The VCM will also turn ON the fuel pump for 2 seconds when the ignition is turned to the OFF position.


Object Number: 155977  Size: FS

Scott K and 4 other Chevy Specialists are ready to help you
Customer: replied 8 years ago.

no ecm voltage at fuel pump(purple wire)

Expert:  Scott K replied 8 years ago.

The purple wire is for the fuel pump gauge, the grey wire is voltage for the pump.


does the relay click on an ignition cycle?


Does the ECMB fuse have voltage both sides?


Below is gauge schematics

Object Number: 155975  Size: FS


Customer: replied 8 years ago.
the relay click during cycle and the grey wire has power and we have power at the ecmb fuse
Expert:  Scott K replied 8 years ago.

In your original post you stated pump will run if wired direct, if direct wiring means providing a power and ground... then we have just proved that the vehicle is supplying the power now we need to check the ground.


Next step is to check the ground wire.


On the fuel pump connector connect a voltmeter lead on the gray wire and the other lead on the black wire.


The fuel pump grounds at G402 and is connected there via a splice pack SP423. these locations are for the 4door blazer if yours is 2 door let me know.

Near top center of second cross-member from rear, with fuel filler neck ground strap

notice the arrows


Object Number: 357334  Size: LF


(1)Trailer Wiring Provision
(2)Splice Pack SP423
(3)Evaporative (EVAP) Emissions Canister Vent Valve
(5)Fuel Filler Neck Ground Strap

Customer: replied 8 years ago.
has 11.8 volts
Expert:  Scott K replied 8 years ago.


Then the problem is the connection at the pump.


check to make sure terminals inside fuel pump connector are tight. these may have spread or burnt causing a bad connection.


And was the meter placed on the solid black wire(C) and not the black with white stripe(D)?


Fuel pump connector.


Object Number: 280761  Size: CH


Wire Color

Circuit No.





Fuel Gauge Sensor Signal




Fuel Pump Motor Feed








Sensor Return


Scott K and 4 other Chevy Specialists are ready to help you
Customer: replied 8 years ago.

that worked thank you very much would never of thought of that.

Expert:  Scott K replied 8 years ago.

Thank you glad i could help


Good luck with the blazer



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