2012 Yukon XLT with mystery rough idle and misfire codes

[gotliebk]

I've never pulled a head on a vehicle but there is a first time for everything. If I pulled the head, how would I know if the cam is worn or not? We are talking about .03" on one lobe. How do you measure something round to that kind of tolerance? Also, how do you know I have the updated VLOM? Is it by the year/model? Thanks for your input here. I'm facing a big decision on this vehicle and I can use all the insight I can get.

The 2012 model year came with updated VLOM and AFM lifters. I believe they actually started shipping them in mid-2011. Maybe the shop always replaces all lifters, the VLOM, etc. when they find a problem lifter. Given your problem wasn't a collapsed AFM lifter, it would appear your VLOM and AFM lifters (V4 mode) are working fine. I just found it odd they would feel the need to replace it.

You aren't going to have .030" of "normal wear" on a cam lobe. That is more than half the lift of the whole lobe, so it is going to be a kind of binary thing. Either the cam lobe is going to look normal (looking down at it, after the head, lifters and trays are removed), or it is going to looked all scored and damaged. Frankly you will probably know when the problematic lifter is removed. If the roller looks fine and normal, the cam will almost certainly look the same.

We have had a couple of members in recent weeks find lifters where the roller was damaged and the cam obviously as well (the roller rolls on the cam lobe). One was a guy where one of his lifters roller had seized and did a job on the cam lobe. He too had lost lift and found the problem with a misfire on that cylinder. He had to replace the cam and lifter (decided to do them all). More recently we have a very experienced member who had replaced his lifters and cam and had a bad lifter tray cause his lifter to turn, causing it to damage both the roller and cam lobe. Again he is replacing the cam and lifters (along with the bad trays).

In your case, you don't know yet. I believe in guys fixing their own cars, but unless you have a fair amount of mechanical experience, what your journey of discovery might entail could be more than maybe a guy who changes his own oil might want to bite off. If you had a real gear head friend you could entice to come over and lend a hand, then I would probably say go for it, because even the full job as described by the shop isn't outside the skill level of one and a half gear heads. The difference in price would be a lot. The parts to do everything the shop said they would do would likely come in about $1500, so that and enough beer to keep your friend coming back probably gets it done. If you two found just a bad lifter, under $500 would likely get you back on the road with all new lifters on that banks side.

For a guy who has never pulled a head, my advice would be to keep looking for a good (and reasonable) shop. You know enough now to know what the minimum and maximum the job might entail.

BTW, all of the above is just one guy on the internet's opinion.

Thanks for all the insight. Is it possible to pull the lifters for the #3 cylinder without removing the head just to inspect the rollers? I've also got a borescope to run down the bore and at least examine the cam lobes. This would be something I think I would attempt myself if it could be done without removing the head as you mentioned previously. I see conflicting opinions on the forums about whether this is even possible on the LS engines. Most posts say you have to remove the head but a few videos I've seen show lifters being removed and replaced through the bore with a special tool. These videos were not for the motor I have as far as I could tell.

 

[CaptainAmerica1]

Head has to come off to get to the lifters and trays. Head removal and replacement is like a 2-3 on a scale from 1-10. Just get the torque values correct when you reassemble. No big deal buddy.

 

[BG1988]

O2 sensors are bad that will cause a random misfire


air fuel ratio issue

whats the fuel trim?

 

[BG1988]

Thanks for all the insight. Is it possible to pull the lifters for the #3 cylinder without removing the head just to inspect the rollers? I've also got a borescope to run down the bore and at least examine the cam lobes. This would be something I think I would attempt myself if it could be done without removing the head as you mentioned previously. I see conflicting opinions on the forums about whether this is even possible on the LS engines. Most posts say you have to remove the head but a few videos I've seen show lifters being removed and replaced through the bore with a special tool. These videos were not for the motor I have as far as I could tell.

someone was offering 10,000$ reward if you found away to do that without removing the head(if you found away to remove the rollers without taking the head off)

So I took my 2012 Yukon to a specialty shop and had them redo the diagnostics. Got a lot more detail this time around but the same diagnoses.

From the shop:
Note:
Checked For Injector Pulse and Spark Pulse. Found Good. Listened To Injector With Stereoscope and And Compared To Other Injectors. Sounds The Same. Performed Compression Test. Cylinder 3 150psi. Checked Cylinder 1 150psi. Found With in Spec. Listened To Rocker Arms With Stethoscope. On Cylinder 3 Makes Excessive Clatter Noise. Removed Valve Cover To Inspect. Put Dial Indicator On Tip Of Rocker Arm On Cylinder 1 and Cylinder 3. Found That Cylinder 3 Has .030 Less Lift. Indicates Issue With Worn Cam Shaft and Lifters. Rec Replacing Cam Shaft All Lifter, Lifter Cups and Vlom. Check Valves and Valve Guides After Heads Are Off.

Now for the painful part. They recommend I replace the camshaft (for wear) and all the lifters, gaskets, and VLOM. Here is their quote:

View attachment 350265
Does this analysis make sense? Does a .03" difference in lifter travel enough to make a valve not seal? Any other way I can address this?

find the parts your self it's way cheaper

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the head gasket is only 90$ for the set

 

[wsteele]

Thanks for all the insight. Is it possible to pull the lifters for the #3 cylinder without removing the head just to inspect the rollers? I've also got a borescope to run down the bore and at least examine the cam lobes. This would be something I think I would attempt myself if it could be done without removing the head as you mentioned previously. I see conflicting opinions on the forums about whether this is even possible on the LS engines. Most posts say you have to remove the head but a few videos I've seen show lifters being removed and replaced through the bore with a special tool. These videos were not for the motor I have as far as I could tell.

I don’t know of a way to inspect/replace lifters without removing the head.

I went back to my notes and I may have given you bad information about the timing of GM’s upgrades to the VLOM. I could not find a model year reference. I think maybe the only way to know what rev VLOM you have is to look at the part number. But again, number 3 isn’t an AFM lifter so your AFM appears to be working fine.

If you decide you want to try pulling the head, make sure you have a plan for what you are going to do if you find the cam needs replacing. None of this stuff is all that tough and there are a lot of very experienced guys on this site who usually are willing to help, but there is a pretty big jump from pulling the head and replacing lifters and trays to replacing the cam (and all the stuff that comes with the “since you are in there” logic). Make sure if you go down that route, you can see it through.

It also would be really helpful to know the actual results of that leak down test. It would help filling in the puzzle pieces.

 

[donjetman]

Thanks for all the insight. Is it possible to pull the lifters for the #3 cylinder without removing the head just to inspect the rollers?

No

If your cam and/or lifter have lost .030" lift, THAT'S BAD!! It's sending metal into the oil pan that will ruin the oil pump that will totally ruin the engine eventually.

Roundup the parts yourself and find a mechanic that moonlights if you can't afford $4500.

 

[RED TAHOE LS]

Replace # 3 plug wire........I don't see you mentioned it.
They are carbon fiber, as a word of caution !!!!........stay away from oil quick service shops......their well trained to sell $$$$$$$$

 

[mattbta]

I read head gaskets were hard to source this summer, but holy hell - that's an insane price. Even with 2x head gaskets, 2x valve cover, 1x intake manifold, 1x TB...that is quite the markup.

 

[kevlac]

To the OP - Did you ever resolve your issues?

 

[gpracer1]

Slap a higher ratio rocker arm on the suspect lobe/lifter and see if the misfire goes away.