If you are having any problems with the Fuel Pressure Regulator...it may be Leaking Fuel into the FPR Vacuum Line as an indication of an impending failure. THIS Article should Help:
Are you experiencing fuel pressure issues with your 5.3 Vortec engine? It could be a faulty fuel pressure regulator. Learn more and fix the issue today!
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HERE is How to R&R The Fuel Pressure Regulator:
...and another Pro Mechanic's impression...
EFI Diagnostics:
Modern GM Multec II Fuel Injectors are simply "Fancy Solenoids" that are controlled using PWM Signals (Pulse Width Modulation) coming from the PCM (Power Train Control Module) and produce very discreet bursts of Atomized Fuel controlling the ON Time that the EFI Pintles assume to stay Open, supported by the Constant, Regulated Fuel Pressure feeding through the Fuel Rail(s) from the Electric Fuel Pump.
Caveat Emptor:
If the EFIs are NOT Performing Properly... the PCM WILL Flag itself due to Lean Misfires; either a P0300
(possibly caused by a Vacuum Leak or Ignition Issues) ...or... a P0301 - P0308 on a V8 Engine as occurring on either Bank 0 or Bank 1, depending upon where the Poorly Performing EFI is situated.
The Chances that a P0300 will occur and point to a Failure of ALL of the EFIs at once... is simply Astronomically Unlikely.
To be more comprehensive... Modern GM Engines control the AIR entering the Intake System by measuring it as fractions of Gram Weight - Per Second by means of a (MAF) Mass Air Flow Sensor informing the PCM to add this information and adding to its Engine Regulation calculus. Likewise, taking the Temperature of the Air on the way into the Throttle Body using the (IAT) Inlet Air Temperature Sensor is a necessary part of this calculus.
The PCM is always trying to establish the "Driver's Intent" by using the position of the (ACC) Module (Gas Pedal) along with the positions registered by the (TBS) Throttle Body Sensor AKA (TAC) Throttle Actuator Control Module for determining the physical location of the Butterfly Throttle Plate at all times. These Multiple inputs help to inform the PCM.
Other Sensors are also at play here that include the (MAP) Maximum Absolute Pressure Sensor present to measure the amount of Vacuum inside the Intake Manifold as well as the (VSS) Vehicle Speed Sensor mounted to pick up the RPM at the Transmission Output Drive Shaft all coordinating as a protective mechanism against allowing Fuel to be injected if the "Driver's Intent" is to either Drive SLOWLY or if the Driver has applied the Brake Pedal in order to STOP or SLOW the Vehicle.
The Upstream O2 Sensor mounted in the Exhaust Manifold gets the First Taste of the Exhaust Plume coming from all of the Cylinders to determine whether or not the "MIX" or 'Right Ratio of Air to Fuel' (14.7:1) at Sea Level is occurring at all times.
The Oxygen Sensor measures the amount of "Spare Oxygen" left over in the Exhaust Stream
AFTER Combustion and thus, will inform the PCM of just how Efficient
(or Inefficient) its Decision Making has been with allowing Sufficient
(or NOT Enough) Fuel to get Sprayed from the EFI's into all of the Cylinders at any given moment In Balance with the Weighed-In Naturally Aspirated AIR.
This entire process is accomplished by the PCM being able to use "Controlled, Measured, Metered Amsounts of AIR" as its Prime Concern
...and is NOT like The Carburetors of Old, where the Fuel Delivery Method was provoked using the Cylinder Vacuum and a Venturi Shaped Intake Throat in its Opening (Bernoulli's Principle) as the Dominant means for ingesting Gasoline Vapors. But ... If the Modern GM PCM gets even
slightly *confused* by the misdirection from
ANY of these Sensors... its Default Software Calibration Safety Protocol response is to cause the Engine to
SHUNT into a
Reduced Power Mode.
It is impossible to visualize how well or how inefficient the EFIs are performing without using an Oscilloscope. This device is capable of taking a
VERY High Number of Signal Samples in Minuscule Slices of Time, either ALL AT ONCE by using a Low Amperage Current Clamp (By Induction) applied upon the 12 Volt Power Feed Wire
(Primary Voltage Side) of the EFI Array in what is called a "Parade" or... Singly of only One Fuel Injector IN ACTION at a time after Back-Probing its Signal Wire and then viewing its LIVE
(Secondary Voltage Side) Wave Form Behavior On Screen.
The "SHAPES" or "WAVE FORMS" of these Electrical Signals are displayed On Screen as "Voltage Over Time" using an X-Y Axis and with the knowledge of useful "Known GOOD Wave Forms" versus whatever Live Wave Forms show up on the Oscilloscope Screen that lend themselves to make such comparisons. Using the unique, collected examples of "Known GOOD Wave Forms " from other's Library of Experiences... a Good Automotive Diagnostician will be able to determine just How Well
(or How Poorly) the EFIs are performing.
THIS Video is a CLASSIC Example of How to Use an Inexpensive
Hantek Model #1008C Oscilloscope to Back Probe an array of Fuel Injectors and View their Performances On Screen. THIS is an Illustration of what a Normal "GOOD KNOWN" EFI Wave Form
SHOULD look like:
If you are interested... More Training and Instructions on "How To Use An Inexpensive Oscilloscope" can be found at THIS Link:
You don't need a Huge Bag of Coins in order to obtain and use an Oscilloscope for performing In-Depth Wave Form Analysis in Automotive Applications on everything from Problematic Electronic Fuel Injection to obtaining accurate Compression Tests to Diagnose Internal Engine Conditions. HANTEK...
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