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2009 Sierra won't start

Soooooo red

By Soooooo red
in Ask A GM Technician

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Soooooo red Enthusiast

Soooooo red

Posted
Posted

Hi guys. My 2009 Sierra 5.3 4wd won't start. Threw p0172 & 175 codes about a week ago. Cleaned maf and couldn't find any intake leaks. Cranks then almost stalls then rpms go up and down till it warms up. Today it started and then stalled and won't start. Any ideas?

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

^^^ What he said. That will tell you quite a bit.

 

Codes are for too much fuel. Could be a junk regulator, stuck open purge valve, or stuck open injector (not likely since on both banks, but still possible to have more than one bad ones).

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

What is the fuel pressure running, and on a snap-throttle?

 

If it stays that high, you've got a bad regulator.

Soooooo red Enthusiast

Soooooo red

Posted
  • Author
Posted

I'd love to tell you but I can't get it started. Just charged the battery so I'll go try again.

Is the regulator part of the pump assembly on this model? I'm having trouble finding any info on it.

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Ahh, these new ones might not have a regulator anymore, since they're returnless setups. Was just going to edit my last post to mention that. I don't know a whole lot about the fueling systems on the '07 up models, and even less about the GDI ones ... but that's neither here nor there ..

 

What is the pressure while cranking?

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Donald, how can it need a pump if it's building pressure? Not being a smart-ass - is the regulating done at the pump? I thought the newer ones were done PWM by the PCM?

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

Ahh, nevermind - I found the info I needed:

 

 


Circuit/System Description
The engine control module (ECM) supplies voltage to the fuel pump control module (FPCM) when the ECM detects that the ignition is ON. The voltage from the ECM to the FPCM remains active for 2 seconds, unless the engine is in Crank or Run. While this voltage is being received, the FPCM closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank pump module in order to maintain the desired fuel rail pressure.

The fuel system is an electronic returnless on-demand design. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

The fuel tank stores the fuel supply. An electric turbine style fuel pump is contained by the fuel pump module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel pump module. The function of the venturi pump is to fill the fuel pump module reservoir. The fuel pump module contains a reverse flow check valve. The check valve maintains fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

 1. Ignition ON, engine OFF, command the FPCM Fuel Pump ON with a scan tool and observe the fuel pressure gauge while the fuel pump is operating. Verify the fuel pressure is between 345–690 kPa (50–100 psi).
⇒ If the fuel pressure is greater than the specified range, replace the fuel tank fuel pump module.
⇒ If the fuel pressure is less than the specified range, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank fuel pump module.
◦Restricted fuel feed pipe
◦Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
 2. After the fuel pump is turned OFF, verify the fuel pressure stabilizes between 500–599 kPa (72–87 psi).
⇒ If greater than the specified range, replace the fuel tank fuel pump module.
 3. After the fuel pump is turned OFF, verify the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 minute.
⇒ If the pressure decreases more than the specified value, perform the following procedure:
3.1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief.
3.2. Install the J 37287 Fuel Line Shut-off Adapter between the fuel feed pipe and the fuel rail.
3.3. Open the valve on the J 37287 Fuel Line Shut-off Adapter .
3.4. Ignition ON, command the FPCM Fuel Pump ON with a scan tool and bleed the air from the CH-48027 Digital Pressure Gauge .
3.5. Command the FPCM Fuel Pump ON and then OFF with a scan tool.
3.6. Close the valve on the J 37287 Fuel Line Shut-off Adapter .
3.7. Monitor the fuel pressure for 1 minute.
⇒ If the fuel pressure decreases more than 34 kPa (5 psi) within the specified time, locate and replace the leaking fuel injector(s).
⇒ If the fuel pressure does not decrease more than 34 kPa (5 psi) within the specified time, replace the fuel tank fuel pump module.
 4. Relieve the fuel pressure to 69 kPa (10 psi). Verify that the fuel pressure does not decrease more than 14 kPa (2 psi) in 5 minutes.
⇒ If the fuel pressure decreases more than the specified value, replace the fuel tank fuel pump module.
 5. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 Digital Pressure Gauge . The fuel pressure should not drop off during acceleration, cruise or hard cornering.
⇒ If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank fuel pump module.
◦Restricted fuel feed pipe
◦Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
 6. If the fuel system tests normal, refer to Symptoms - Engine Controls.
After reading this, I'm thinking that you may only need a fuel pressure sensor, since the pressure is high. The no start may or may not be related to this.
Scratch that - that pressure is normal after reading the troubleshooting steps.
Back to basics. You've got fuel pressure. Now you need to know if you've got spark, and injector pulse.

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