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Replaced fuel pump 3 times, now dies when giving gas or under load.

kaczman

Full Member
Joined
Jan 18, 2013
Messages
185
2007 Avalanche 1500 5.3L Vin 3 LC9 Flex Fuel Truck.

I was having a large evap leak and the fuel level was reading off with less than 1/4 take full of gas. I decided to replace the fuel pump.

Dropped tank, replaced fuel pump with one from autozone. Fired it up, and problems. When you start it up and idle, it is fine. As soon as you give it gas, it dies, and then backfires through the intake. Tested fuel pressure at the rail, it has 50 psi at idle and then drops to 8 psi under load.

Assumed it was a bad fuel pump. Got another new unit from autozone. Same exact thing. Contacted local GM dealership, ordered a new pump off the Vin, a GM unit. Installed it, same problem.

If you give it gas and the engine dies, the stabilitrack light comes on, but scanning with a Tech2 there are NO CODES.

We are 100% stumped.
 
Bad Gas? ....

when you had gotten the new pump was it just the pump or fuel filter also? ... wonder if you have a clogged filter or crap stuck in the fuel line ....

 
Also check the fuel pressure regulator.... When you blip the throttle or pull the vacuum line off it should jump to 60psi give or take a psi or two..
 
Randy said:
Also check the fuel pressure regulator.... When you blip the throttle or pull the vacuum line off it should jump to 60psi give or take a psi or two..

I believe by 07 they went to returnless fuel systems so the pressure regulator should be on the pump itself???
 
Intimidatoruag said:
Bad Gas? ....

when you had gotten the new pump was it just the pump or fuel filter also? ... wonder if you have a clogged filter or crap stuck in the fuel line ....

Thanks for the response guys.

No, same gas as when I drove all last week. The new pump contains a new filter, as well as regulator.
 
The ECM uses ignition pulses to regulate fuse pump. I not sure were it see it from.
 
That's right I didn't pay attention to the year.. My bad..
 
I copied this from my manual



Fuel Metering Modes of Operation

The engine control module (ECM) monitors voltages from several sensors in order to determine how much fuel to give the engine. The ECM controls the amount of fuel delivered to the engine by changing the fuel injector pulse width. The fuel is delivered under one of several modes.


Starting Mode

When the ignition is first turned ON, the ECM energizes the fuel pump relay for 2 seconds. This allows the fuel pump to build pressure in the fuel system. The ECM calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in starting mode until the engine speed reaches a predetermined RPM.


Clear Flood Mode

If the engine floods, clear the engine by pressing the accelerator pedal down to the floor and then crank the engine. When the TP sensor is at wide open throttle (WOT), the ECM reduces the fuel injector pulse width in order to increase the air to fuel ratio. The ECM holds this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the ECM returns to the starting mode.

Run Mode

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The ECM ignores the signal from the heated oxygen sensors (HO2S). The ECM calculates the air/fuel ratio based on inputs from the ECT, MAF, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions:
   
? Both front HO2S have varying voltage output, showing that both HO2S are hot enough to operate properly.
    ? The ECT sensor is above a specified temperature.
    ? A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the ECM calculates the air/fuel ratio, injector ON time, based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.



Acceleration Mode

When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly. To prevent possible hesitation, the ECM increases the pulse width to the injectors to provide extra fuel during acceleration. This is also known as power enrichment. The ECM determines the amount of fuel required based upon the TP, the ECT, the MAP, the MAF, and the engine speed.

Deceleration Mode


When the driver releases the accelerator pedal, air flow into the engine is reduced. The ECM monitors the corresponding changes in the TP, the MAP, and the MAF. The ECM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to prevent damage to the catalytic converters.


Battery Voltage Correction Mode

When the battery voltage is low, the ECM compensates for the weak spark delivered by the ignition system in the following ways:
    ? Increasing the amount of fuel delivered
    ? Increasing the idle RPM
    ? Increasing the ignition dwell time

Fuel Cutoff Mode

The ECM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability:
    ? The ignition is OFF. This prevents engine run-on.
    ? The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
    ? The engine speed is too high, above red line.
    ? The vehicle speed is too high, above rated tire speed.
    ? During an extended, high speed, closed throttle coast down--This reduces emissions and increases engine braking.
    ? During extended deceleration, in order to prevent damage to the catalytic converters



 
The injectors have nothing to do with the fuel pump.  The previous post explains how the ecm controls the amount of fuel into the cylinders.  Fuel pump is not involved except to provide sufficient fuel at the rail at 0a constant pressure.  It appears there is a something in the fuel system preventing the pump from supplying sufficient volume to meet the ecm demand.  Could be a restriction in the line, or the tank is not being vented properly, or the new pump is defective.  Been offroad or ran anything over recently?  The fact that you have 50 psi with a low demand indicates to me the pump can make pressure, I would look for kinks in the lines.  Good luck.
 
MS03 2500 said:
Who said anything about that.

Your entire post #7 discusses how the ecm adjusts the injector duty cycle under various operating conditions.

Has nothing to do with the fuel pump issue of the original post.

To answer your implied question,  you did.  Have a nice day.
 
joe in va said:
Your entire post #7 discusses how the ecm adjusts the injector duty cycle under various operating conditions.

Has nothing to do with the fuel pump issue of the original post.

To answer your implied question,  you did.  Have a nice day.
It was copied from the manual, Don't start attacking before you read all the content. This forum is here to help people and get information. Keep it civil.  Thanks 
 
Well the description was how it controls the fuel pressure using fuel regulator in the gas tank not the injectors.

I do not attempt to try to tell anyone what is wrong because I'm not there and I don't have a crystal ball, I show them how it works


I did have a nice day thou, sunny and warm here,


 

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