• If you currently own, previously owned or want to own an Avalanche, we welcome you to become a member today. Membership is FREE, register now!

P0306 Cylinder 6 Misfire - 2008 5.3L

uconnjack

Full Member
Joined
Mar 23, 2015
Messages
13
My 2008 5.3L 4WD with ~135K miles has recently been throwing a P0306 cylinder 6 misfire, along with a Stablitrak warning.  It first happened a couple weeks ago but only lasted a day.  I cleared the code and it was fine for another couple of weeks before it happened again today.  It does go through a lot of oil (probably a at every 1,000 miles), and there is a clicking sound.

I know from researching this the last couple weeks that its likely failure of the #6 cylinder lifter and/or plug fouling due to the AFM system design and/or old PCV cover.  I intend on doing some diagnostics this weekend including inspecting and replacing (if needed) plugs/wires/coils, doing compression tests, and pulling off valve covers to look for stuck lifters/valves. 

My questions are:

1)  Other than the obvious, is there anything else I should be specifically looking out for when running these tests?

2)  Are there are any other diagnostic tests I should be doing while I am in there.

3)  Assuming compression test is fine, and replacing plugs/wires stops the misfires, can I hold off on replacing a bad lifter if there is one?

4)  I would plan on getting a Range tuner to disable AFM (which I should have done when I bought the truck 3 years ago) and replacing the valve cover with the new one.  If the compression test is OK suggesting there is (currently) no ring, gasket, valve, etc. damage, would these measures stave off more issues? 

5)  If a lifter is bad and I really need to replace it now, can I just replace the one, or do I need to replace them all?  Also, how difficult is it to take the passenger side head off to access the #6 lifters? 

6)  If it does fail compression, am I likely screwed and looking at a rebuild or replacement?

7)  Any other advice, recommendations, or thoughts?

Thanks in advance!

 
Sorry I don't have an answer for you, but I have a similar problem with cylinder #7. I have the revised valve cover, though. I read at least one post where people had a #7 code but it turned out other cylinders were misfiring.

The most common problem for the #7 is oil fouling from the AFM, but I didn't think it affected #6.

My diagnosis process has been this so far:
- Inspected the plug - looks good and no different from the other 3 on that cylinder bank
- Moved the coil and wire to another cylinder. Didn't fix it
- Moved the plug to another cylinder. Didn't fix it

I'm going to move an injector next. There is a TSB out there where crud collects in the back of the fuel rail over time and affects the fueling at the rear cylinders, including #7. The fix is to remove the rail, clean it, and do a top-end clean. In addition to the 307 code, I have lean codes so I'm thinking that might be my problem. I have 176k on mine and I'm just trying to keep it road worthy for a backup vehicle. My SES light went out on its own today and I was able to sneak through state inspection and get a good, 2-year sticker. My incentive to fix it is much lower now, but I'll get to it if it ever stops snowing here in NJ.

 
Sorry I don't have an answer for you, but I have a similar problem with cylinder #7. I have the revised valve cover, though. I read at least one post where people had a #7 code but it turned out other cylinders were misfiring.

The most common problem for the #7 is oil fouling from the AFM, but I didn't think it affected #6.

My diagnosis process has been this so far:
- Inspected the plug - looks good and no different from the other 3 on that cylinder bank
- Moved the coil and wire to another cylinder. Didn't fix it
- Moved the plug to another cylinder. Didn't fix it

I'm going to move an injector next. There is a TSB out there where crud collects in the back of the fuel rail over time and affects the fueling at the rear cylinders, including #7. The fix is to remove the rail, clean it, and do a top-end clean. In addition to the 307 code, I have lean codes so I'm thinking that might be my problem. I have 176k on mine and I'm just trying to keep it road worthy for a backup vehicle. My SES light went out on its own today and I was able to sneak through state inspection and get a good, 2-year sticker. My incentive to fix it is much lower now, but I'll get to it if it ever stops snowing here in NJ.
Sorry to bring up an old thread, but i'm at this exact same mileage and just experienced the same thing in cylinder 6 last night. Did you manage to solve your issue? I also have a stabilitrack service warnin.
 
There are a bunch of good videos on youtube about this issue. Search under Silverado though. There are way more of them and they are the same platform if you have the 5.3. I was going to link one for you but there are a ton to pick from.

Good luck
 
Thanks. Got it cased. No compression. Motor shot, ~$10,000 replacement at 108k mi, even though it's been treated with full synthetic it's entire life. This will be the last GM product I spend my money on :(
 
DId they check the valves and lifter?
If lifter collapses valve will stay open and look like no compression but would pump air out either intake or exhaust
 
I hope $10k is not the result for you. Where I live (Texas) there are shops that specialize in LS swaps and engine swaps for $1k-$1500k in labor. A nice reman 5.3 should run about $3k-$4k. Not that $5k is an easy pill to swallow but $10k seems kinda high ? I could be wrong.

Good luck with it, I suppose I am driving a grenade that I hope doesn't go off. Stupid AFM lol...
 
Back
Top