P0306 Cylinder 6 Misfire - 2008 5.3L

uconnjack · February 23, 2018

My 2008 5.3L 4WD Avalanche 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 coverwith 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?

4) 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?

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

6) Any other advice, recommendations, or thoughts?

Thanks in advance!

carnau · February 23, 2018

If you have access to a tech 2 I would test drive it and command it in and out of AFM. If the skip comes and goes you know it is a lifter failure (which is what it is most likely.)

Replace the number 6 lifters and VLOM (Valve lifter oil manifold) and you will be back in the game. It is actually a pretty simple job. Sounds like a lot of work but I can normally knock them out in about 3 hours per side. Also the #6 side is easier since you don't have to fight the alternator bracket or the steering shaft when taking the manifold off (not that either of those are super hard to do)

The valve cover isn't going to cause this issue either. Also I would do exactly what you said and check all my compressions and everything before replacing anything. But if it only happens in AFM lock you know what the problem is. $600 and a day of work and you're back on the road.

Parts list if you want it.
Here is the Kit comes with all the head bolts and everything. Cheaper than buying everything individually. - http://amzn.to/2sQ3oVS

Here is the VLOM(not a necessity nut I would recommend) - http://amzn.to/2ENcwMA

uconnjack · February 23, 2018

Thanks for the advice! Hopefully compression is still good and there doesn't seems to be any seized rings or damage. I've done a lot of car work between suspension, drivetrain, etc. but I haven't gotten into an engine yet, so I am a little nervous about taking off the head cylinders if I need to replace lifters. They can be removed without removing the engine or too many accessories, correct? If it comes to that, I will get a Haynes/Chiltons and watch all to YouTube videos I can, but are there any tips or trick I should keep in mind?

muddkatt · February 23, 2018

I would contact https://www.texas-speed.com/

and get the delete kit and a tune. Here is the delete kit: https://www.texas-speed.com/p-7379-dod-afm-delete-kit-for-536062-engines.aspx

swathdiver · February 24, 2018

If you're going to do the minimum, then plan on doing it again as the other parts are likely to fail as well. If you're going to keep AFM, get all the updated parts so that it is more reliable, the improved Delphi II De-Ac lifters, the improved VLOM and updated valve cover, etc. Deleting AFM will get you Gen III reliability with Gen IV toughness. You'll need to replace the camshaft and get a tune and if your chosen camshaft has more than .510 lift or so, you'll NEED new springs. There are camshafts by Crane and Cam Motion that offer plenty of power down low without the need for new springs.

Your LC9 has a single pattern camshaft, all but one of the replacements are dual pattern, with more lift and duration on the exhaust side. Fun stuff.

carnau · February 28, 2018

On 2/23/2018 at 2:52 PM, uconnjack said:

Thanks for the advice! Hopefully compression is still good and there doesn't seems to be any seized rings or damage. I've done a lot of car work between suspension, drivetrain, etc. but I haven't gotten into an engine yet, so I am a little nervous about taking off the head cylinders if I need to replace lifters. They can be removed without removing the engine or too many accessories, correct? If it comes to that, I will get a Haynes/Chiltons and watch all to YouTube videos I can, but are there any tips or trick I should keep in mind?

It really is a pretty simple job. Just remove and replace. Make sure you use new head bolts and proper torque. You really won't have a problem. If you get somewhere you don't know whats going on shoot me a PM or I can give you my cell and I can guide you through it.

Deejay · January 2, 2021

Just letting you all know I had a misfire on cylinder 4 on my 08 suburban also the ticking noise on motor and the stabilitrack going off! a friend gave me a tip and it worked after changing spark plugs, swaping the coil and I still had the same problem!! the tip was to change the oil but instead using 4 quarts of the recommended oil AND 2 quarts of the Rotella diesel oil believe it ir not the ticking sound dissapeared like in the 5th day!! hey its worth the shot!!