07 Avalanche 5.3 Magnacharger & Big Lsr cam: Fuel Pressure questions

[G_Force]

While tuning a 2007 Avalanche with the 5.3 LC9 and Magnacharger and a BIG Comp LSR cam, I needed to make a few adjustments to the Injector Delta Pressure table. So I added the PID's for "Inj Delta Pressure" and "Fuel Pressure (SAE)" to my table display in the VCM Scanner (2.25). I can see the Inj Delta Pressure value changing based on MAP sensor loading changes (which is normal), while the Fuel Pressure (SAE) remains fixed at 399.0 kPa (4 bar). Maybe the fuel pressure is regulated so well the it never does change, unless the demand out-strips the supply. I don't know. So I decided to check on where the Fuel Pressure sensor is located in this truck and based on the VIN, the parts search only shows a "Fuel Tank Pressure Sensor". I did the same parts search for my 2012 Corvette based on its VIN and also found the same thing ... only a "Fuel Tank Pressure Sensor". No Fuel Pressure Sensor at all !!

I did find a Fuel Pressure Sensor on a 2011 GMC 1/2Ton Pickup with the 9.2(2) L9H engine, so GM is building vehicles with a Fuel Tank Pressure sensor AND Fuel Pressure Sensor. But since many of the vehicles we work on seem to only have a Fuel Tank Pressure Sensor, how in the world does the "Fuel Pressure (SAE)" PID get its data, when there is no Fuel Pressure Sensor in the system?

I am also in the midst of an engine swap project with a 2013 Corvette LS3 in a Street Rod (non emiss) and was planning on not using the Fuel Tank Pressure sensor; disabling the appropriate DTC's for this sensor. But, will I end up with issues related to the Fuel Pressure PID and how the E38 ECM calculates the Inj Delta Pressure value?

[schpenxel]

Fuel tank pressure sensor is for emissions stuff, evap, etc., you can disable it no problem.

I'm almost sure that vehicle doesn't have a fuel pressure sensor. I know the Corvette doesn't. The 4 bar value you're getting is probably hard coded somewhere, not actually measured from a real sensor.. so I think you're way overthinking this. Forget about a factory fuel pressure sensor.

[G_Force]

As far as the Fuel Tank Pressure Sensor goes, I fully agree that it is an emissions compliant component and a Low Pressure device, like only a couple of pounds of pressure, I think. I knew that I could disable it easily enough.

But, I needed to hear comments (like yours) regarding the Fuel Pressure measurement/display thing. I was just hoping that in dealing with engine swaps, that I was only going to utilize sensors that were absolutely necessary. So yes, I will nix the Fuel Tank Pressure sensor, but if the donor engine & ECM system has a Fuel Pressure sensor in the configuration, I will use it, otherwise won't worry about it. Thanks!

[schpenxel]

My 2007 Escalade is the same way. You can log fuel pressure but it's literally just one flat lined value. It's not possible the fuel pressure is really that stable. It's got to be a hard coded value. Probably in preparation for the PWM fuel systems used on some other models with similar ecm's. Mine reads 399 Kpa also so I very much believe there isn't a fuel pressure sensor.

Hopefully someone else can confirm

[JDV]

My 2007 Escalade is the same way. You can log fuel pressure but it's literally just one flat lined value. It's not possible the fuel pressure is really that stable. It's got to be a hard coded value. Probably in preparation for the PWM fuel systems used on some other models with similar ecm's. Mine reads 399 Kpa also so I very much believe there isn't a fuel pressure sensor.

Hopefully someone else can confirm

Fuel System Description

Fuel System Overview

The Fuel System is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender assembly, eliminating the need for a return pipe from the engine. 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.

An electric turbine style fuel pump attaches to the fuel sender assembly 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 provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel sender assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. The fuel pressure regulator, a part of the fuel sender assembly, maintains the correct fuel pressure to the fuel injection system. The fuel pump and sender assembly contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

E85 Flex Fuel Description

E85 compatible vehicles no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle calculates the alcohol content of the fuel through measured adjustments.

The ethanol calculation occurs with the engine running after a refueling event has been detected via a measured change in the fuel level sender output. The virtual flex fuel sensor (V-FFS) algorithm temporarily closes the canister purge valve for a few seconds and monitors information from the closed loop fuel trim system to calculate the ethanol content. This logic executes several times until the ethanol calculation is deemed to be stable. This may take several minutes under low fuel flow conditions such as idle, or a shorter time during higher fuel flow, off-idle conditions.

Air-fuel ratios and the corresponding ethanol percentage are updated following each purge-off sequence. the fuel alcohol content percentage value can be read on a scan tool.

When an E85 compatible vehicle is built, an ECM or PCM replaced, or if the learned alcohol content has been reset with a scan tool the fuel system will need to contain ASTM gasoline with 10 percent or less ethanol content.

A minimum of 11 Liters (3 gallons) must be put in the tank in order for the vehicle to recognize a re-fueling event. It is not necessary to turn the ignition off in order to have the re-fueling event recognized; however local safety regulations should be followed.

After the re-fueling event, the system registers the amount of fuel that was added, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines if the fuel added was either ASTM Gasoline or ASTM E85. Based on that determination, the system adjusts to the expected alcohol mix in the fuel tank, and then the fuel trim and O2 sensor activity fine tunes the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or E85 to gasoline, can result in driveability symptoms due to the inability of the system to adjust for fuel composition by not attaining closed loop operation.

Switching Between Gasoline and E85

No special precautions need to be taken when switching back and forth between gasoline and E85 other than re-fueling events must be 11 Liters (3 gallons) or greater, and the vehicle must remain in closed loop long enough, usually by the time the engine has maintained full operating temperature, to calculate the composition of the new blend in the tank.


This GM's Description an operation

Fuel Tank Pressure Sensor

The fuel tank pressure (FTP) sensor measures the difference between the pressure or vacuum in the fuel tank and outside air pressure. The control module provides a 5-volt reference and a ground to the FTP sensor. The FTP sensor provides a signal voltage back to the control module that can vary between 0.1–4.9 volts. A high FTP sensor voltage indicates a low fuel tank pressure or vacuum. A low FTP sensor voltage indicates a high fuel tank pressure.

Basically a two bar map looks just like a map used on older vortec 4.3 an 5.7 Hope this helps .

[JDV]

Here is fuel pump circuit goes directly to relay not a module so it is not pulse width modulated this year range so everything is hard coded an set based off internal regulator in sending unit . when they come up with values from what I know from school it is based off armature bars on pump motor electric side , an number of vanes / or gear rotor style on mechanical end of pump .

[schpenxel]

Awesome, thanks! I have access to that info, not sure why I didn't think to just look up the wiring diagrams, lol

[G_Force]

I did examine the wiring diagrams and ECM pinouts to determine that the 2007 truck and the 2012 Vette don't have a Fuel Pressure Sensor, but I was still wondering if it was derived from another source. Apparently the fuel pressure value is indeed hard coded. As others have noticed, the fuel pressure value of 399 kPa never budges and remains fixed, as displayed by the PID.

Thanks for all the great background info, guys!