Unlocking lifter.....VLOM problem?

Ryan Bokros · December 29, 2016

Ok, new guy here! So I know that there is and has been a ridiculous ongoing issue with the AFM lifters sticking or collapsing entirely and all that mess. I have a 2007 GMC Sierra 5.3 Flex Fuel 4X4 - 160k miles. Pretty regular maintenance, I am not OCD, but I try to do my best at around 3500-400 miles - full synthetic Mobile 1 oil, AC Delco Filter, every other change gets a half quart of MMO.

Here is my situation....

No ticking whatsoever (which I know is usually attributed to this), BUT recently a terribly bad misfire on Cyl 4 (one of the AFM cylinders) and throwing the typical 304 code with stabilitrak warning. Before pulling the valve covers, I checked EVERYTHING (well, except compression, should have done that) - I checked plugs (a little black, but not wet), coils, injectors, fuel and oil pressure, etc. That is what led me to go ahead and pull the valve covers to check for any slack in the rockers/valves due to a collapsed lifter (even though there is no noticeable tick). Initially pulling the covers, I was pleased with how clean everything was....and how tight everything was. No slack in the rockers whatsoever, from what I could tell the valve springs look good, etc!! Yay...but WTF is causing this?

Well, I fired up the truck and found that the intake valve in cyl 4 was not moving. BUT...when my wife got home, I had her turn the engine over for me so I could see it all without doing it myself. Here is what I am confused about - on start up, the valve moves...once maybe twice, it goes through the whole compression cycle then stops once the engine is running...when the engine it turned off, it does the same thing - one or two cycles. If it was collapsed or busted, it wouldn't push the valve at all, would it? Could this be the VLOM and not the lifter? My oil pressure reads well, so I am not experiencing low pressure like others I am reading, but I am aware of the filter leading to the VLOM...maybe that is the next step. Thoughts?

Thanks!!

newdude · December 29, 2016

GM dealers have the special tools to test the VLOM so I'd say next step would be the dealer either with the truck, or to see if they can test the VLOM for you. The GM test equipment has a solenoid control box and shop air supply. They pump 30psi to the VLOM and then use the control box to run each solenoid to test their function.

When in V8 mode, the VLOM solenoids are in the closed position thus not letting oil flow to the lifter locking pins. When the solenoids are turned on, oil is sent to the lifter locking pins and disengage the pins to allow the lifter to "collapse." If you have a VLOM solenoid sticking ON, that would explain why it is collapsing the lifters thinking it is in V4 mode. The fact that you can start up and then it starts to miss, would lead be to believe that the solenoid for cylinder 4 may be sticking open and sending oil to the lifters and collapsing them for V4 function.

If you aren't worried about testing the existing VLOM, its $316.68 at a local dealer p/n 12571609. You will need intake gaskets as well $111.82 p/n 89060413.

Me? It wouldn't hurt to have the VLOM tested if you already have the truck apart yourself just to make sure its bad before you drop $500 on parts and its a bad lifter.

Ryan Bokros · December 30, 2016

Thanks....that is kind of what I have been thinking. At this point, I only have the valve covers off, so its pretty easy to get back together and to the dealership.

Since the lifter is engaging, I'm cautiously optimistic that it isn't the lifter and is the VLOM as you also suggested.

I'll update moving forward.

On another note....I ordered the Range AFM Delete module and will be shutting of the AFM once I figure this situation out!! What a pain this thing is and I'm baffled that GM has never truly addressed it....

leoshorty · May 2, 2018

Mine dropped the intake lifter on #4 twice in short order (less than 2500 miles). The first time had damaged the cam enough it was allowing the lifter to rotate, thereby eating up the lifter guide. Did a complete AFM delete, cam, lifters, valley, and program from AMS Racing in Bossier. About $700 and so far has been good but I’m only a couple hundred miles in.

Edited May 2, 2018 by leoshorty

bobradley4 · February 23, 2019

Sorry to restart this thread. I was hoping someone could shed some light for me. I had a 2014 Silverado L83 engine. Came in ticking and skipping. All the basics were in tip top shape. So we removed the heads and found a non dod lifter on number 8 to have locked up and ate the cam up. Customer not wanting to put a performance cam in it so we replaced cam and all lifters back to OE. We also had the ecm shipped off and the afm deleted from it. We got it back together and started the engine. It has a skip on number 6 which is a dod cylinder. We removed valve cover and Started it. The valves worked fine until oil pressure built up and then both rockers stopped moving. Contacted the cut who deleted the afm from ecm and he said it has to be the VLOM. So I purchased a new VLOM from the dealer. Started it back up and doing same thing. I know it isn’t the computer turning it off because I have the 5 pin connector that plugs into the VLOM disconnected. Would anybody know what’s causing this?

16JeepRubi · April 29, 2019

Bobradley4,

Were you able to repair your 2014? I am curious as to what caused your number eight cylinder to have a misfire since you replaced the VLOM.

After the VLOM replacement, did you remove the valve cover and see the same valves not being actuated?

Did it turn out to be ECM? Thanks for your help with this.

Rog88 · May 24, 2019

I have the same issue with #4 cylinder was anyone able to fix and what was the cause?

ChuckyCRB · October 5, 2019

I have replaced intake lifter #4. Now 3 months later and about 7000 miles, it has collapsed again! Any Ideas?

CamGTP · October 6, 2019

More a case of bad luck than anything if you ask me.

You could replace the lifter again and do the whole VLOM plate if you truly wanted too.

ChuckyCRB · October 6, 2019

I would have to order the plate. was wondering if maybe replace the lifter again and leave the plate disconnected? Or would that cause a check engine light?

CamGTP · October 6, 2019

It would trip the light and maybe cause a poor running condition.

There are ways to disable the system. Be it a tune or the range OBD2 dongle thing that will shut off the AFM/DoD system.

ChuckyCRB · October 6, 2019

Got the head pulled. The lifter was stuck. While trying to remove it it fell apart. Maybe I had just bought a bad lifter? I got it out. The lifter cavity seems to be ok. NEW lifter slides easily

swathdiver · October 21, 2019

On 10/5/2019 at 5:28 PM, ChuckyCRB said:

I have replaced intake lifter #4. Now 3 months later and about 7000 miles, it has collapsed again! Any Ideas?

Yes, you need to replace the VLOM and Lifter Guides too. This is SOP with AFM repair. It is the failure of a VLOM solenoid that causes the lifters to collapse because of a missed timing event. If yours was built before April 2011 or so, get the new valve cover for the driver's side too. (Well, make sure someone didn't replace it already).

TheBigOldDog · January 7, 2020

For those interested in this common problem and how to fix it, sometimes very inexpensively, go to youtube and search for the name CrazedPerformanceRepair and watch his videos, especially, Lifter Release Trick Collapsed Lifter AFM DOD GM Chevrolet Lifter Noise He even sells a tool to release the lifter without even pulling the heads. He explains in detail why this happens in the video, Determine GM v8 Block Type, Why it's Important. He also shows how to midify the VLOM.