Mechanics

CHEVY NO POWER TO THE FUEL PUMP

1999 Chevrolet Blazer

Electrical problem
1999 Chevy Blazer 6 cyl Two Wheel Drive Automatic 170000 miles

There is no power at the fuel pump all the fuses are good. When the key is on there is power to three of the legs on the relay. There has been a couple of times when there was power back at the pump but only a few times. Tried adding a ground but that didnt help. Was wondering if the ecm may not be sending signal to the fuel pump?Kind of at a loss on this one.
thanks in advanced for your help
Avatar
Zoomer55
January 15, 2009.




Hello. Thanks for the donation. Much appreciated.

Is the security light flashing or staying on?. The PCM cuts fuel if there is a fault on the Passlock system. If the PCM was not sending signal to pump the oil pressure switch would still start off the pump? Let me know

FUEL DELIVERY
Fuel Pump
An in-tank, electric fuel pump delivers fuel to injector(s) through an in-line fuel filter. The pump is designed to supply fuel pressure in excess of vehicle requirements. The pressure relief valve controls maximum fuel pump pressure.
On Central Sequential Port Injection (CSI) systems, pressure regulator is mounted to fuel metering body under upper intake manifold. On Sequential Multiport Fuel Injection (SFI), pressure regulator is attached to end of fuel rail. Pressure regulator keeps fuel available to injector(s) at a constant pressure. Excess fuel is returned to fuel tank through pressure regulator return line.
When ignition switch is turned to ON position, PCM turns on electric fuel pump by energizing fuel pump relay. PCM keeps pump on if engine is running or cranking (PCM is receiving reference pulses from ignition module). If there are no reference pulses, PCM turns pump off within 2 seconds after ignition is turned on.
Most models also include a second control path through the oil pressure switch which will turn the fuel pump on after the switch detects oil pressure. Cranking time will be longer if fuel pump does not receive current until oil pressure switch contacts close.

PASSLOCK(tm) SYSTEM
When mechanical key turns Passlock(tm) lock cylinder, a Resistance Code (R-Code), is created by a rotating magnet turning past a stationary Hall Effect sensor. R-Code is sent to the BCM. The BCM determines validity of R-Code within a preset time window, then sends a coded password over the class 2 serial data line to the Powertrain Control Module (PCM)/Vehicle Control Module (VCM), which then allows fuel injectors to operate normally.
If BCM sends a password that is different than learned password in PCM/VCM, the PCM/VCM will enter no start mode. During this mode, fuel injectors are shut off for 10 minutes and SECURITY indicator light will stay on. Engine may crank and temporarily start, but will soon stall due to fuel shut-off. If a large magnet is placed near Passlock(tm) sensor, a tamper signal will be sent to BCM. The system is continually self diagnosing certain functions. If a malfunction exists, system will store a Diagnostic Trouble Code (DTC). BCM does not illuminate Malfunction Indicator Light (MIL). If a Passlock(tm) DTC exists, BCM illuminates SECURITY indicator light.

Dave H
Jan 15, 2009.
Thanks Dave

With the key on and after its cranked the security light is not flashing or steady. Does the power go from the relay back to the pump or relay to pcm then to the pump?Cause I always have power on three legs of the relay but not always at the pump.

Tiny
Zoomer55
Jan 17, 2009.
The PCM (computer) sends a signal to the RELAY which energizes the PUMP. The PCM gets it's signal pulses from the IGNITION MODULE so if the MODULE is not working the PCM cut's power to the RELAY/PUMP after 2 SECONDS. ALSO the OIL PRESSURE SWITCH will energize the fuel pump after it has reached the correct pressure, if the pump does not recieve a signal from the IGNITION MODULE/PCM/RELAY. When you first sit in the vehicle. Make sure everything is turned OFF (radio/heater) in the car. Turn ignition to ON (no crank). Do you hear a 2-5 second buzz noise inside the vehicle. Try this a couple of times to see if you hear the BUZZ. Also could you let me know how you checked for power @ pump. Did you check the actual wires on pump? Let me know?

When ignition switch is turned to ON position, PCM turns on electric fuel pump by energizing fuel pump relay. PCM keeps pump on if engine is running or cranking (PCM is receiving reference pulses from ignition module). If there are no reference pulses, PCM turns pump off within 2 seconds after ignition is turned on.
Most models also include a second control path through the oil pressure switch which will turn the fuel pump on after the switch detects oil pressure. Cranking time will be longer if fuel pump does not receive current until oil pressure switch contacts close.

Dave H
Jan 18, 2009.
We started this project by thinking it was just a bad fuel pump replace pump and it did not work so then removed pump and check wires for power at the tank.
AD

Tiny
Zoomer55
Jan 18, 2009.
From relay orange wire/relay pin A6/C2 is HOT all times to PCM 12volts

grey wire/relay pin F1/C3 is feed to pump

dark green white wire/relay pin A10/C1 is fuel pump control signal from PCM which would then put power to grey wire/relay pin F1/C3

black wire/relay pin F7/C2 is ground

could you tell me what color wires you have at the pump ... my diagram is showing.. grey .. relay feed wire, hot @ key on for 2 seconds then hot @ cranking and hot @ engine running .. then 2 black wires which are grounds .. and a purple wire going to the PCM which is fuel level signal .. if you are hot @ the relay you must have a break/short in the wire between relay and pump .. let me know ..


http://www.2carpros.com/forum/automotive_pictures/266999_fuel_8.jpg


Dave H
Jan 18, 2009.

AD