H3 Need Help with Intermittent rough start up!

[Cyouincourt007]

My 08 H3 with 103k miles does the same thing sometimes when starting. It stutters a bit and varies from high rpm to lower and them Settles down to normal. Hmmmm if I give it a bit of gas when it does this it reves up and then settles down to normal. Either way it doesn't happen all the time and it doesn't last long either just s few missteps and then back to normal. Hmmmm

 

[Joebot8484]

Yup that's the same issue I have.

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[Cyouincourt007]

Yup that's the same issue I have.

Sent from my SCH-I535 using Tapatalk

any news on this? Mine still does it intermittently....yesterday at startup dipped real low in Rpms then it revved up high and settled back to normal. Today same again as if about to stall. Happens and then Doesn't happen for a while sometimes...I did notice that it happened when my fuel level is low or at least it was yesterday and today when it happened. I'll keep an eye on that to see if it happens like that again...just grasping for straws I guess....

 

[Joebot8484]

I really haven't looked any more into the issue. I've spent lots money and time researching this problem with no solid results. I'm looking at doing an engine swap in the future, that will fix the issue haha.

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[awjohnson2]

Did you figure out what the guage reading should be when the truck is off?

CONVERSION CALCULATOR

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[h=3]2008 Hummer H3 L5-3.7L[/h]
Vehicle » Powertrain Management » Fuel Delivery and Air Induction » Fuel Pressure » Specifications

• SPECIFICATIONS

Fuel Pressure

Fuel Pressure (Key ON, Engine OFF)

380-410 kPa (55-60 psi)

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[awjohnson2]

[h=3]2008 Hummer H3 L5-3.7L[/h]
Vehicle » Powertrain Management » Fuel Delivery and Air Induction » Fuel Pressure » Service Precautions

• SERVICE PRECAUTIONS

Relieving Fuel Pressure Caution

Caution: Remove the fuel tank cap and relieve the fuel system pressure before servicing the fuel system in order to reduce the risk of personal injury. After you relieve the fuel system pressure, a small amount of fuel may be released when servicing the fuel lines, the fuel injection pump, or the connections. In order to reduce the risk of personal injury, cover the fuel system components with a shop towel before disconnection. This will catch any fuel that may leak out. Place the towel in an approved container when the disconnection is complete.




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[awjohnson2]

[h=3]2008 Hummer H3 L5-3.7L[/h][h=3]
Vehicle » Powertrain Management » Fuel Delivery and Air Induction » Fuel Pressure » Testing and Inspection » Fuel System Diagnosis

• FUEL SYSTEM DIAGNOSIS

Fuel System Diagnosis

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection\Initial Inspection and Diagnostic Overview\Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis (See: Testing and Inspection\Initial Inspection and Diagnostic Overview\Strategy Based Diagnosis) for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions (See: Testing and Inspection\Initial Inspection and Diagnostic Overview\Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

Circuit/System Description

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel tank module, 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.

The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel tank module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter, contained in the fuel tank module, 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 tank module. The function of the venturi pump is to fill the fuel tank module reservoir. The fuel pressure regulator, a part of the fuel tank module, maintains the correct fuel pressure to the fuel injection system. The fuel tank module 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.

Reference Information
Description and Operation

Fuel System Description (See: Computers and Control Systems\Description and Operation\Fuel System Description)
Electrical Information Reference

• Circuit Testing (See: Testing and Inspection\Component Tests and General Diagnostics)
• Connector Repairs (See: Testing and Inspection\Component Tests and General Diagnostics)
• Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection\Component Tests and General Diagnostics)
• Wiring Repairs (See: Testing and Inspection\Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (See: Testing and Inspection\Programming and Relearning) for scan tool information
Special Tools

• CH-48027 Digital Pressure Gage
• J 37287 Fuel Line Shut-off Adapter

Circuit/System Verification

Important:

• Inspect the fuel system for damage or external leaks before proceeding.
• Verify that adequate fuel is in the fuel tank before proceeding.
• The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
• Before proceeding with this test review the User Manual CH-48027-5 for Safety Information and Instructions.

1. Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool. You should hear the fuel pump turn ON and OFF.

¤	If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis (See: Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Fuel Pump Electrical Circuit Diagnosis) .

1. Ignition OFF, all accessories OFF, install a CH-48027 . Refer to Fuel Pressure Gage Installation and Removal (See: Fuel Pressure Gage Installation and Removal) .
2. Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 345-427 kPa (50-62 psi) and does not decrease more than 34 kPa (5 psi) in 1 minute.

[/h]

 

[awjohnson2]

Circuit/System Testing

Important:

• The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
• DO NOT start the engine.

1. Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating. Verify the fuel pressure is between 345-427 kPa (50-62 psi).

¤	If the fuel pressure is greater than the specified range, replace the fuel tank 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 module.

• Restricted fuel feed pipe
• Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.

1. Verify that the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 minute.

¤	If the fuel pressure decreases more than the specified value, perform the following procedure:

1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief (With CH 48027) (See: Fuel Pressure Release\Service and Repair\Fuel Pressure Relief (With CH 48027))Fuel Pressure Relief (Without CH 48027) (See: Fuel Pressure Release\Service and Repair\Fuel Pressure Relief (Without CH 48027)) .
2. Install the J 37287 between the fuel feed pipe and the fuel rail.
3. Open the valve on the J 37287 .
4. Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the CH-48027 .
5. Command the fuel pump relay ON and then OFF with a scan tool.
6. Close the valve on the J 37287 .
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 module.

1. 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 module.

1. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 . 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 module.

• Restricted fuel feed pipe
• Inspect the harness connectors and the ground circuits of the fuel pump for poor connections

1. If the fuel system tests normal, refer to Symptoms - Engine Controls (See: Computers and Control Systems\Testing and Inspection\Symptom Related Diagnostic Procedures\Symptoms - Engine Controls) .

Repair Instructions

Perform the Diagnostic Repair Verification (See: A L L Diagnostic Trouble Codes ( DTC )\Testing and Inspection\Verification Tests) after completing the diagnostic procedure.

• Fuel Hose/Pipes Replacement - Chassis (See: Fuel Return Line\Service and Repair)
• Fuel Injector Replacement (See: Fuel Injector\Service and Repair)
• Fuel Tank Module Replacement (See: Fuel Tank Unit\Service and Repair)

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[btrevisa]

Did you resolve this issue? I think I have the same problem. btrevisa@gmail.com

 

[Happy Hummer]

Echo... hello....hello...lol!
Crickets!

 

[btrevisa]

Hello, I were you able to solve your intermittent h3 problem? I am having the same issue?

 

[alrock]

No one has been in this thread in five years, and it was started nine years ago. And most of the people posting are not active here. I'd recommend starting a new thread and describing your symptoms to see if anyone here can help.