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GM Bob
GM Bob, ASE Certified Technician
Category: GM
Satisfied Customers: 1103
Experience:  30 plus years experience as GM technician, ASE Master Technician and GM Certified.
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GM YUKON: I HAVE A 2004 GMC YUKON AND I HAVE A P0300 CODE

Customer Question

HI I HAVE A 2004 GMC YUKON AND I HAVE A P0300 CODE AND I HAVE DONE A COMPLETE TUNE-UP AND I STILL HAVE THE SAME CODE, WHAT COULD BE THE PROBLEM?
Submitted: 1 year ago.
Category: GM
Expert:  GM Bob replied 1 year ago.
Hello my name is ***** ***** I can help.Does your scan tool show misfire history or current misfire data? This would help narrow down which cylinder is missing. Do you feel the misfire?Have you check for spark?How does it run down the road?Sorry for so many questions Please get back with me Thank you
Customer: replied 1 year ago.
I do have spark I feel the misfire when I'm driving and the check engine light flashes intermittently
Expert:  GM Bob replied 1 year ago.
Does it misfire at idle?Do you have a scan tool?Ha
Customer: replied 1 year ago.
I believe so I a Snap On Soulus
Expert:  GM Bob replied 1 year ago.
Can you find the data list for misfire?It should show what cylinder is missing.
Customer: replied 1 year ago.
It showing cylinder number seven and cylinder number two on the live data screen
Expert:  GM Bob replied 1 year ago.
which one is counting up faster?
Customer: replied 1 year ago.
I am looking at a graph of line goes up and moving
Expert:  GM Bob replied 1 year ago.
Sometimes one cylinder will make another show a misfire
Customer: replied 1 year ago.
How would you determine which one what information do I need
Expert:  GM Bob replied 1 year ago.
With a long screwdriver can you listen to each injector. When its running.Make sure 2 and 7 are clicking. Sound the same as a good cylinder
Customer: replied 1 year ago.
It looks like cylinder seven is more sporadic all over the place
Expert:  GM Bob replied 1 year ago.
You could pull off a spark plug wire see if it misfire worse. If it don't that is the cylinder
Customer: replied 1 year ago.
Here's pic of # *****
Customer: replied 1 year ago.
Here's #7 also it looks like number six shot up and misfired for a second very weird
Expert:  GM Bob replied 1 year ago.
It was missing before the tune up?Yes it looks like 7
Expert:  GM Bob replied 1 year ago.
How was the spark plug you took out?Any oil fouled
Customer: replied 1 year ago.
Yes it was misfiring before the tune up so from the pictures you believe I should replace number seven and it should shouldn't need number two? No there was no oil
Customer: replied 1 year ago.
I also did a compression test compression was good
Expert:  GM Bob replied 1 year ago.
Is there any engine noise? ticking
Customer: replied 1 year ago.
No
Expert:  GM Bob replied 1 year ago.
Was the compression the same as a good cylinder?
Customer: replied 1 year ago.
Yes sir
Expert:  GM Bob replied 1 year ago.
Have you tried swapping coil and wire?See if it moves
Customer: replied 1 year ago.
I have not I have 3 coils just in case should I replace the 2 cylinders misfiring ?
Expert:  GM Bob replied 1 year ago.
I would start with #7. It is the left side rear cylinder.Just making sure we are on the correct cylinder
Expert:  GM Bob replied 1 year ago.
There is still chances you may have a bad injector.
Customer: replied 1 year ago.
OK will do number seven left rear if you're sitting in the vehicle
Expert:  GM Bob replied 1 year ago.
correctAlso listen to the injector make sure its clicking loud like a good cylinder.Keep me postedThank you
Customer: replied 1 year ago.
So I replaced cylinder seven and cylinder two coils and I still have the same problem I have sporadic up-and-down on other cylinders could there be an intake leak
Customer: replied 1 year ago.
Not sure what's going on!! Errr driving me crazy!! Lol
Expert:  GM Bob replied 1 year ago.
If it was a intake leak. You would have lean codes.
Also you would not feel it going down the roadHow did the injectors sound?
You could swap injectors see if it moves
Expert:  GM Bob replied 1 year ago.
I have had catalytic convert cause misfire on one cylinder.
If you remove the front O2 sensor.
See it gone.
Customer: replied 1 year ago.
So I am looking at the cylinder misfire data cylinder seven is at 22,31,45,55,65,72 then it goes back to 0 and keeps misfiring
Customer: replied 1 year ago.
After changing the intake manifold gasket now I have bank one PO 171 code system to lean any ideas
Customer: replied 1 year ago.
So now I have cleared the codes and only the PO 300 code comes back
Expert:  GM Bob replied 1 year ago.
The misfire counter goes to 100 and resets. This is normal.Did you do anything with the injector????
Expert:  GM Bob replied 1 year ago.
Did the P0171 lean condition come back?
Expert:  GM Bob replied 1 year ago.
Just checking to see how you are doing.
Customer: replied 1 year ago.
Still have major misfire 7 maybe a cam bearing
Expert:  GM Bob replied 1 year ago.
Ok here is a check list. Let me know if you did it or not. Swapped coil and spark plug wire? Check new spark plug? See what it looks like after running with misfire? Compression test? Would like to see the results Swapped Injector or replaced? Removed front O2 sensor out of exhaust on left side? Test drove see if misfire is gone? Remover left valve cover look at rocker arms? See if they are moving same as the other cylinders. This engine will run with the coils off on one side. Please get back with me