When it comes to Troubleshooting Automotive Diagnostics, the Value of Watching THIS particular Video cannot be measured, especially for the uninitiated. Let’s Follow Along with VOP (Video Original Poster) as he Delves into WHY this 2005 Chevrolet Trailblazer intermittently Starts and Stalls:
2005 Chevrolet Trailblazer 4.2L LL8 A4
Symptoms: Intermittent Starts with Stalls. NOTE: The Measurements taken below are UNIQUE.
Recent Repair Work: Electric In-Tank Fuel Pump Replaced.
Key On Engine Off: Normal Dash Collision Lights appear on the IPC.
Key On Engine Off: Turn Off the Radio & Heater to be able to HEAR the Fuel Pump Running.
Check Engine Light: Comes ON with Release of the Ignition Key.
Step-By Step Diagnostic and Repair Tools:
Snap-On Verus Bi-Directional Scan Tool
Snap-On Vantage-Pro Graphing Electrical Meter.
Fuel Pressure Gauge with LONG Hose-Line
Relay “Fuse Buddies”
Incandescent Test Light
3/8” Drive Ratchet with 10-13mm Sockets
Replacement Copper Wire and OEM Grommets
Lead Core Solder
Heat Shrink Wire Insulation
Step-By-Steps and Observations:
No Fuel Under Pressure escaped during the Fuel Pressure Gauge Hook Up.
Key On Engine Off, Fuel Briefly Pressurized to 55 PSI.
Key On Engine ON, Engine Almost Starts, Runs Briefly & Dies after Rapid Fuel Pressure DROP.
Key On Engine ON, Re-Start Fails (No Fuel Pump Prime).
Set Up Snap-On Verus to DLC & Auto-ID the Vehicle (No Gauges, Dash Lights or Odometer).
The Snap-On Verus went directly into the BCM Screen, Select Engine & Look for any Codes.
No Codes Found, Select “Bi-Directional Controls” to Engage the Fuel Pump
Select “Functional Tests”, “Output Controls”, then “Fuel Pump Relay”
Bi-Directional Control of Fuel Pump Relay Fails (NO Clicking).
Under Hood Fuse Panel Image below shows Fuel Pump Relay as #41, Outlined in RED:
Pull Relay# 41 and Insert Relay “Buddy” Jumper to Probe and Actuate the Relay Externally.
The Fuel Pump RUNS and Fuel Pressure appears on the Analog FP Gauge.
This is Proof that The Problem is with the Control Side, causing a Relay Malfunction.
Attach the Test Light Probe Lead to GROUND and Poke Pin 86 of Relay “Buddy” in #41.
Test Light Probing of 86 Has Power, Fuel Pump RUNS with Test Light Probing 85 of #41.
Test Light is DIM when Probing 86 indicating a Poor Ground (Fuel Pump FAILS to Work).
Test Light on 85 of Relay #41 DIM, indicating a Voltage Drop.
Snap-On Vantage Pro has the Positive Lead is Hooked to 85 and with a Battery Ground.
The Volt-Meter Read Out shows only “6.6 Volts DC”, Proving a Voltage Drop at the Supply.
Possible locations are The Fuse Box-Panel or another Relay. Refer to the Electrical Diagram.
Power to the FPR coming FROM the PCM, means that the FP is NOT Ground Side Controlled.
Using the Snap-On Verus, Command the FP ON & Observe the Voltage Draw on the Vantage Pro.
When connecting the Voltmeter across the Control Side of Relay #41, it Draws 11.5 Volts DC
When connecting the Voltmeter across the Control Side of Relay #41, The Fuel Pump RUNS.
This means that there is a BAD GROUND and that is located at G-107 on the Engine Block:
The Snap-On Vantage Pro Volt Meter shows a serious Voltage Drop when the Fuel Pump Runs.
This Test was performed between the Ground Position on the Engine Block @ G-107 & Relay#41.
The Voltage DROP was recorded there was 7.57 Volts. This is Abnormally HIGH when FP Runs.
A Physical Inspection revealed that the G-107 Ground Wire HAD BROKEN OFF OF THE TANG.
A Replace Tang and Length of Wire was Soldered and Shrink Wrapped to prevent future corrosion.
The Follow Up Voltage Drop Test at the G-107 Position was down to a Nominal 0.17 Volts DC.
Key On Engine On ... Vehicle Starts... Take the Vehicle for a Test Drive and Repeat the On-Off Cycle.
Professional Test Procedures are always THE Thoughtful, Organized and Deliberate Approach to follow to Improve upon a Diagnostician's Skill Set.
Note: ALL of these Procedures are captured in the attached PDF and available for Download:
2005 Chevrolet Trailblazer 4.2L LL8 A4
Symptoms: Intermittent Starts with Stalls. NOTE: The Measurements taken below are UNIQUE.
Recent Repair Work: Electric In-Tank Fuel Pump Replaced.
Key On Engine Off: Normal Dash Collision Lights appear on the IPC.
Key On Engine Off: Turn Off the Radio & Heater to be able to HEAR the Fuel Pump Running.
Check Engine Light: Comes ON with Release of the Ignition Key.
Step-By Step Diagnostic and Repair Tools:
Snap-On Verus Bi-Directional Scan Tool
Snap-On Vantage-Pro Graphing Electrical Meter.
Fuel Pressure Gauge with LONG Hose-Line
Relay “Fuse Buddies”
Incandescent Test Light
3/8” Drive Ratchet with 10-13mm Sockets
Replacement Copper Wire and OEM Grommets
Lead Core Solder
Heat Shrink Wire Insulation
Step-By-Steps and Observations:
No Fuel Under Pressure escaped during the Fuel Pressure Gauge Hook Up.
Key On Engine Off, Fuel Briefly Pressurized to 55 PSI.
Key On Engine ON, Engine Almost Starts, Runs Briefly & Dies after Rapid Fuel Pressure DROP.
Key On Engine ON, Re-Start Fails (No Fuel Pump Prime).
Set Up Snap-On Verus to DLC & Auto-ID the Vehicle (No Gauges, Dash Lights or Odometer).
The Snap-On Verus went directly into the BCM Screen, Select Engine & Look for any Codes.
No Codes Found, Select “Bi-Directional Controls” to Engage the Fuel Pump
Select “Functional Tests”, “Output Controls”, then “Fuel Pump Relay”
Bi-Directional Control of Fuel Pump Relay Fails (NO Clicking).
Under Hood Fuse Panel Image below shows Fuel Pump Relay as #41, Outlined in RED:
Pull Relay# 41 and Insert Relay “Buddy” Jumper to Probe and Actuate the Relay Externally.
The Fuel Pump RUNS and Fuel Pressure appears on the Analog FP Gauge.
This is Proof that The Problem is with the Control Side, causing a Relay Malfunction.
Attach the Test Light Probe Lead to GROUND and Poke Pin 86 of Relay “Buddy” in #41.
Test Light Probing of 86 Has Power, Fuel Pump RUNS with Test Light Probing 85 of #41.
Test Light is DIM when Probing 86 indicating a Poor Ground (Fuel Pump FAILS to Work).
Test Light on 85 of Relay #41 DIM, indicating a Voltage Drop.
Snap-On Vantage Pro has the Positive Lead is Hooked to 85 and with a Battery Ground.
The Volt-Meter Read Out shows only “6.6 Volts DC”, Proving a Voltage Drop at the Supply.
Possible locations are The Fuse Box-Panel or another Relay. Refer to the Electrical Diagram.
Power to the FPR coming FROM the PCM, means that the FP is NOT Ground Side Controlled.
Using the Snap-On Verus, Command the FP ON & Observe the Voltage Draw on the Vantage Pro.
When connecting the Voltmeter across the Control Side of Relay #41, it Draws 11.5 Volts DC
When connecting the Voltmeter across the Control Side of Relay #41, The Fuel Pump RUNS.
This means that there is a BAD GROUND and that is located at G-107 on the Engine Block:
The Snap-On Vantage Pro Volt Meter shows a serious Voltage Drop when the Fuel Pump Runs.
This Test was performed between the Ground Position on the Engine Block @ G-107 & Relay#41.
The Voltage DROP was recorded there was 7.57 Volts. This is Abnormally HIGH when FP Runs.
A Physical Inspection revealed that the G-107 Ground Wire HAD BROKEN OFF OF THE TANG.
A Replace Tang and Length of Wire was Soldered and Shrink Wrapped to prevent future corrosion.
The Follow Up Voltage Drop Test at the G-107 Position was down to a Nominal 0.17 Volts DC.
Key On Engine On ... Vehicle Starts... Take the Vehicle for a Test Drive and Repeat the On-Off Cycle.
Professional Test Procedures are always THE Thoughtful, Organized and Deliberate Approach to follow to Improve upon a Diagnostician's Skill Set.
Note: ALL of these Procedures are captured in the attached PDF and available for Download:
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