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My 2013 Yukon XL Project

BigDogYJ

BigDogYJ

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Let’s see how far this goes….


I picked up a high mileage 2013 GMC Yukon XL SLT 1500 4WD last week with a misfire and lifter knock on cyl 6.
Odometer shows 184k miles, but GM dealer replaced the engine at 88k miles due to a failed afm lifter. So current motor has just under 100k and surprise surprise another afm lifter failure. Despite the high mileage this thing is actually really clean. CA truck its whole life, started as an Enterprise Rental for the first 11 months and 24k miles. Then to a private owner down the street from me for the last 8 years as a family hauler. I got it for a steal so couldn’t pass it up.

My plan was to jump head first into a full afm delete. However after reading a lot more and watching some videos I’m tempted to try a trick to release a stuck lifter and see if it comes back to life. If I’m successful then I’ll plan to get it smogged (lovely CA) and just drive it around for a few months to see if anything else major is needed. If it seems pretty solid after that time, then I’ll likely plan for a full afm delete so it can be a solid reliable runner.

I’m usually biased towards 3/4 or 1 ton rigs but after the experience we’ve had with my wife’s current daily (04 Yukon 4WD) I’m curious if the gmt900 is a decent contender once you get rid of that crappy afm system. Time will tell.

Feel free to follow along as I document what I learn and accomplish some things along the way. This is my first foray into the gmt900 platform so it might get interesting…

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Apparently the lifter started knocking and misfiring about 9 miles from the house where they parked it. I did toss in a bottle of MMO in the crankcase and drove it about 6 miles to get it home. Noise seemed to come and go during that drive but still misfiring.

Drained the oil and went through it with a fine screen and magnet, cut open the filter and went through all the filter media/pleats. Found no metal anywhere but definitely noticed some grit in the bottom of the oil filter and in the pleats.
I can't say it was like sand but definitely gritty but smaller particles than sand. not much but it was definitely there. Pictures didn't work to pick it up. so I know the oil that was in there has about 4500 miles on it and they added BG MOA Engine Oil additive at the time the oil was changed (January of 2024). I also added a bottle of MMO before driving home ~ 6 miles. Glad there's no metal but not sure what this gritty stuff was. It was a pretty cheap no brand filter at a quick lube oil place. I filled it with fresh full synthetic 5w-30 and put a new Purolator One filter.

got the intake manifold, passenger valve cover and valley cover off last night. After confirming the intake lifter on #6 was collapsed as expected (checking the rocker arm was flopping back and forth), we proceeded with a trick to shock the lifter and cause it to release. I used a tool from a YT channel (Crazed Performance Repair) I'm sure many of you have come across. Lo and behold it worked. The lifter released and the pushrod popped right out. Checked the push rod to confirm it wasn't bent, cleaned and lubed it and returned it to its home. Then reset the locks on the lifter as he explains in his video. Got the rocker arm and manually rotated the engine to confirm the valve was now opening/closing as it should. Put the valve cover back on and torqued it. This thing is pretty dirty. Not so much sludge but definitely caked on oil residue.

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For a fun comparison.....

The Left image is the passenger valve cover from this 2013 5.3L AFM w/ 94k miles. Appears to be ~10k mi OCI (following the message on the cluster) with cheap synthetic oil and no name filters used.

The Right image is the driver valve cover from our 2004 5.3L NON-AFM w/ 198k miles. 3.5k mi OCI with conventional oil but purolator or mobil 1 filters used.

Clearly these AFM engines need to keep the oil change interval below 5k miles regardless if its synthetic or not.

Your can also see where the rocker arm was smacking the underside of the valve cover in the left image :smh:

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So we picked this up last Tuesday and have been working in it on and off the last week.

So last night we got it all back together and...

Got it all buttoned up and ready to fire with fresh oil, filter and Amsoil motor flush.

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After Two rounds of Amsoil flush (with fresh oil and filter each time) cut open both filters, no debris or metal found in either. Put in a final filter and some Amsoil Signature 5w-30 and let it run for about 30 minutes at idle before driving. Found cyl #3 spark plug was loose (ie I could unthread it by hand). so Pulled it out, inspected and reinstalled.
It still had a significant misfire/stumble. Drove it to the gas station got some Chevron fuel and Techron additive and dumped that in. Drove it for another 10 minutes or so and the misfire was significantly better. I'm betting that the spark plug/injector is just fouled up from the misfiring prior. I'll likely end up changing out all the spark plugs. But there's no active misfire code (flashing CEL) and no lifter noise anymore. So thats a win so far.

Plan is to drive it some more and get some miles on it so that it can complete the emissions monitoring tests we can get it smogged. I'll probably change spark plugs before the end of the week.
I've been driving it in Manual mode to keep it from going to V4 mode right now until It gets a chance to run well enough on 8 cylinders without any rough idle or stumbling. Then I may let it run in full AFM mode and see how it does. Hopefully the lifter doesn't get stuck again right away.

Here's a clip from driving on the highway last night and giving it a little bit of a run...

So far im thrilled it's running without the lifter knock and there was no metal in it. Oil still looks super clean right now. After about 500-1000 miles I'll probably send a sample to Blackstone labs for an oil analysis to see if there's anything to be concerned about.
 
Will L. said:
Nice looking rig, be interesting to see the full process from diag to elimination.

And can I have the pine nuts? 😂
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yeah if everything else checks out then we'll likely go for the arm delete so I don't have to worry about that. other issue sounds like the 6l80e torque converter can take a dump and wipe out the trans so I'll probably want to address that as well.

haha. yeah that squirrel was probably watching me drive it away going damn.....
 
Nice looking rig there! if the seats are just standard ones, iirc these rigs had the option for air conditioned seats. if you can find a good set with that option along with the ducting for them then you can make Marty a deal LOL
 
So I screwed up....

I was driving it around today to get the monitoring tests to pass so we could smog it. Well I was driving it with the trans in M5 and it was passing all the tests without going into v4 mode. I messed up and shifted to M6 and it went to v4 mode and collapsed the lifter instantly and cyl 6 misfire started instantly. Damn...

So I should have been more careful to make sure it wasn't shifting to 6th. Oops.

So tomorrow I'm tearing back into it again and gonna do it all over again.

This time I'll make sure it's in M5 only so it doest go to v4 mode so I can get it to pass the smog check. once that's done I can tune the AFM stuff so it doesn't happen again until I can get the AFM delete done.

Wish me luck.
 
One reason I haven't messed with a GMT900 plus half ton yet. I did really want a GMT900 z71 Suburban, mainly to get away from the torsion bars on the GMT800 and to get the 6-speed trans to help towing my camper. In the end, stuck with my gut and got the 800.
 
Yeah the gmt800 is a pretty solid rig. a few limitations but they just run for a long time. probably my favorite platform thus far.
The gmt900 takes a lot more to get it to that point. there's still some limitations but annoying stuff that seems like GM planned their failures purposely. Headlight design, used to be easy, pull two pins and out it comes. now it's much more involved. door pulls on the door panel are prone to failing and the plastic crumbles and its not a serviceable/easily replaced part unlike the gmt800 where that piece can be unbolted from the rest of the door panel. then gmt900 is all one piece. Im also not a fan of the tiny HVAC buttons and all the dash controls being so low and out of the drivers field of view. just annoying.

on the other hand. you get more powerful engine, 6 speed transmission, coilover front suspension, rack and pinion steering and factory remote start. blah blah. gotta work more to enjoy those benefits I suppose. I"ll see how much it feels worth it when I'm done. haha.
 
any chance replacing that one lifter would help anything? I think you can get to them just by pulling the valve cover and rocker arm. maybe it will drive in v4 at least for a little while?
 
Replacing the one would likely keep that from happening again with that cylinder but you gotta pull the head to pull the lifter. I’m not aware of a way to get it out with the head still on. I’m hoping to hold off pulling the head till I’m ready to delete everything and put non afm stuff in it including the cam.

Either way, got it tore all apart again. Lifter only too two small taps to pop free. Got it all back together. Took about 4 hours from start to finish until it was ready to start. Drove it for about 30 minutes with trans in M5 and 5 of 8 monitoring tests completed. Hope to get the others to finish this weekend and then smog it. Then we can program afm out of it and work on a timeline to source the parts and eliminate all the afm crap. Let’s hope it passes. 🤞
 
Will L. said:
What becomes the difference if only programming out the cylinder change but not replacing the hard parts?
Is there any real testing that showed a huge difference in mileage?
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From what I’ve read it varies +/- 1-2mpg. Ironically some report an increase in mileage others a decrease. I suppose that’s due to driving style, Highway vs stop/go. No difference between programming only vs programming and parts swap. The only reason for the parts swap is to get rid of the collapsible afm lifters which have a history of failing even with afm programmed off.
 
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