Now that I have it running the truck keeps throwing code 3 misfire. Any suggestions on what to check?
Ordered new fuel rail and injectors, checking for vac leak, changing plug in 3, all new coil packs and hoping I find problem. I can’t get it inspected with idiot light on.

 

See this thread .... Acts like it wants to stall/rough idle -No CEL -What To Do:

You are overdoing it with throwing parts at it. You should have just swapped Coil Pack on #3 to a different location and see if the misfire followed that CP for the first step. Now that you skipped past that... see where the misfire goes or if it stays at #3.

Next, review my linked thread and the most recent addition by Hummerz. Let us know if you need more help.

 

Thanks Doc, I actually did do the swapping of coil packs and nothing happened. Also plugs. However, I just went to autozone and bought Carb cleaner and sprayed the injectors where they meet the head and motor started to reduce idle. I have a vac leak. Being lazy I only inspected the fuel injectors o-rings and they looked good and seated tight. Well I had the new o-rings and never replaced them and now I have double work. I ordered a new fuel rail with injectors off eBay for $50 and going to replace all the O’s on that one then do swap. Hoping this corrects leak. That’s what I get for cutting a corner out of pure laziness. Rolling eyes.

 

Keep throwing parts at it, it's your $$$.
Now, you are you throwing used fuel injectors at it, when your vac leak is at the intake manifold?
I still have the original factory installed fuel injectors on my '07 and I don't have a check engine light!
My advice to you is to spend more time doing research (there's a ton of information on this site) and less time throwing parts at it.

 

It was already purchased because when installing the intake the wires in the loom got pinched between the intake and head. My son and I removed it and repaired it but I didn’t think of a vacuum leak throwing the code. I figured it was the injector that was pinched got fried by grounding out. My injectors have 153k on them and the other purchased half that from a wreck. Either way the $50 gives me piece of mind because my son will be driving it and I won’t have to worry about him driving the truck.

Don’t be so pessimistic.... 🤨

 

First, you need to understand that there are people all around the world viewing your posts.
Your misinformation could cause many to lose money just like you.
I have saved my customers $hundreds of thousands$ over the years, many came for a second opinion!
Btw, I will NEVER install USED parts, especially on my kids vehicles!
Just go back and check over your work and check the torque on the manifold bolts.

OBD II Fault Code

• OBD II P0303

Fault Code Definition

• Misfire Detected in #3 Cylinder

P0303 Symptoms

• Check Engine Light flashing
• Rough running, hesitation, and/or jerking when accelerating
• In most cases, there are no adverse conditions noticed by the driver
• In some cases, there may be performance problems, such as dying at stop signs or rough idling, hesitation, misfires or lack of power (especially during acceleration), and a decrease in fuel economy

Common Problems That Trigger Code P0303

• Worn out spark plugs, ignition coils
• Incorrect ignition timing
• Vacuum leak(s)
• Low or weak fuel pressure
• Improperly functioning EGR system
• Defective Mass Air Flow Sensor
• Defective Crankshaft and/or Camshaft Sensor
• Defective Throttle Position Sensor
• Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems:
• https://www.hummerforums.com/forum/h...p-41653/page3/

Common Misdiagnoses

• Fuel Injectors
• Oxygen Sensor(s)
• Powertrain/Drivetrain problems

 

Thats right. There are many like me that ask questions and get answers. If people choose to spend money on a cure god bless. Tell me what I have asked with my situation that’s “misinformation”? I have told anyone what to do, I have asked what to do and in meantime I have found out the issue before anyone actually contributed. Just because I might be new on Hummer forum this isn’t my first forum rodeo. I have a Ford, Benz, and gym forum subscription. Never had anyone tell me in 20 years of asking and answering that I misinformed them or anyone. Thanks for the copy n paste.

I have the shop disk with all the 2007 info from GM. I seen all you posted in the pdf files. However, I pinched wires on the injectors so it safe to assume they could be shorted and wouldn’t be s misdiagnoses.
https://drive.google.com/drive/folde...hZRM2V4AJR9ZtD

The list of possibilities was all checked except for vac leak because from my experience you hear it as motor is running.

The o2’s are a misdiagnosis but i’m replacing because they do go bad and again I want my son having a worry free first car experience.

You call it wasting money i call it piece of mind. I replaced all the sensors and gaskets from the block up.

 

Can you please tell me where exactly your leak was? Maybe a pic? and how you found it?