Just thought I'd put my experience out here since I couldn't find any definitive answer either way and see if anyone has any input.

I bought a 2008 Sierra with a 5.3 super cheap with a stuck AFM lifter. Cam looked good as far as I could tell, so I threw another lifter in and it was back and running great at 208k miles. Immediately used my HP tuners to disable AFM and all has been fine for 15k miles.

Oil pressure seemed a bit low compared to what i've seen (as low as 17ish psi at hot idle in gear). Searching led me to leaky messed up VLOMs and filter screens being a possible cause of lower oil pressures and stuck AFM lifters. I wanted to try a quick cheap fix to bump the oil pressure up and rule out the VLOM, but couldnt find anyone saying definitively what would happen if you swap on a $35 non-AFM valley cover and left the AFM lifters in. Since the system sends oil pressure through the solenoids down to the AFM lifters, it seemed that swapping it with a non-AFM valley cover wouldnt be any different than the AFM system being turned off.

Good news is my oil pressure went up a bit at cold idle and warmed up idle, but I never got to test after a highway trip because i had pretty bad random misses and noises at idle. Best I can figure is my 220k+ AFM lifters or lifter bores or something is letting oil pressure back-fill into the now blocked off AFM passages and is somehow activating the AFM lifters at idle and letting it run very poorly.

Cylinder 4 is always misfiring a few seconds after startup, if i blip the throttle some, cylinder 6 starts misfiring, and if i wait long enough cylinder 1 starts. Cylinder 7 is the one i replaced the lifter on. Seems that maybe if the lifters werent so old they possibly wouldnt let this happen, but i dont see any other reason why the lifters activate unless somehow there's just pressure in the passages now.

I could try the non-AFM valley cover without the o-rings that block off the passages, but it seems they're there for a reason and that wouldnt do me any good since the oil pressure would probably bleed off through there the same if that's the problem, would just be something interesting to try. I swapped the stock VLOM back on and the misses went away and oil pressure dropped back to what it was before. Don't plan on doing the lifters and cam and all that any time soon so i'm just going to roll with it only tuned out unless there's some other quick and cheap solution.

 

Fel-Pro sells the gaskets to stop the oil bleeding. The part number for the 4.8/5.3/6.0 is MS96871. I use them quite a bit, (almost whenever we get low oil pressure issues on an AFM equipped vehicle.) We normally replace the oil pump pickup tube seal and the AFM gaskets at the same time.

 

Man this is old lol. Maybe i'll try that gasket set. Wish I hadn't sold the LS3 valley cover I'd try it again without blocking those off. Either way it was weird. Small chance I didn't delete the codes and that caused the problem but I can't remember it's been so long.

 

I know this is ancient but I just did the same swap last night and I’m having the same problem, my truck has afm turned off as well. Literally same codes and same cylinders throwing misfires now

 

Ok so I've learned a lot about how it all works since I posted this years ago.

You can't remove the VLOM without changing the lifters or they will self activate. The system keeps a low oil pressure in the activation passages to have the system "primed" for quick activation via a slow pressure bleed. If you replace the VLOM and block the ports off with the non-DoD valley cover the pressure builds until it activates the lifters.

You also need to tune out the codes for the AFM VLOM or when it throws a code it will disable the injector on that cylinder.

And if you change lifters to non-DoD and don't change the cam you'll get misfires on those cylinders, though it won't feel as obvious.

 

I’m in the process of a rebuilt vin 3 motor and was going to keep stock cam and change out lifters… so what you are saying is I will still get misfire on dod cylinders???? Dod is deleted out of ecu.

 

that is correct, you must change the cam if you change the lifters

 

Thank you for sharing this. Saved me some headaches.
Thought about getting a headstart on DoD delete by doing tower plugs and valley cover while the intake is off and doing cam/lifters later. Now I know better.
I'll just run with AFM tuned out and do the whole job at once.
Thank you once again.
- Jim

 

Looking at your discussion on lifters and i have a question you may be able to answer.
I have a 2007 Silverado with a 6.0 AFM engine. Number 7 cylinder lifter stuck. Replaced both lifters in the 7 cylinder. And made the same mistake as you with the non AFM valley cover. Pulled the cover of and replaced it with a new VLOM. Reprogrammed the ECM and started the engine.
One of the new from GM AFM lifters will not move. All others appear normal.

Not sure if you can damage them buy using the non AFM valley cover on them. Can’t figure out how the lifter isn’t working with the ECM programmed and a new VLOM and lifter. I used the new VLOM rather than the old just to rule out a bad VLOM trapping oil pressure.

I am trying to not change the cam. Just put 2 new lifters in that cylinder and reprogram the ECM so it doesn’t send the other old AFM lifter into 4 cyl mode.

Thanks

Eric

 

For the love of all things holy, just delete the entire AFM system and be done with it. You MUST change the cam, lifters, and valley cover to delete the AFM properly. Then, adjust the tune to disable AFM/DoD. There are plenty of DoD Delete kits out there. This is ancient news. Everyone knows the DoD lifters are junk. GM has been sued for this already. This should not even be a discussion topic anymore. Just do an AFM/DoD delete and be done with it.

 

You can block the oil feed in the vlom manifold and cut releifs in the tower seals to bleed off any pressure build up. The solenoids vent when deactivated so thats why you cant cap the towers.