Volcom26

Just an FYI for anyone having this P0446 code (or other EVAP code) issues. This GM system is super simple to diagnose when you can read the live EVAP data. Only 4 real problems (besides wire/corrosion damage) start with the easiest and check vent valve is opening/closing, then if purge valve is working, then move to the most difficult (but not hard) is tank pressure sensor reading correctly (gas cap off should be reading about 1.5 volts and -1.5 mmhg) if that is reading way off above or below and/or doesn’t change at all when you take gas cap off it’s likely the pressure sensor. If all good there then move to the physical charcoal canister/check it or vent filter not plugged up. Normally this code comes back to a vent valve or tank pressure sensor. Last pro tip, you can get to the fuel tank pressure sensor without dropping fuel tank or removing drive shaft, it’s on top of the fuel sender ring on gas tank just feel around follow the wiring harness. Jack up driver side to give a little more room. Take your time and it’s a 40 dollar OEM part, pull out old and put in new… I replaced everything and the last thing that fixed it, before I learned the entire system, was dang pressure sensor. Be smart, get a scanner and read the live EVAP data! Good luck you got this!

You know, I’m a 5.3 man for sure love it in my new Trailboss, been that way since trading up from my 1990 5.7 back in 2000 and 2007. They are rock solid and good power/mpg balance as it were. I am also a Honda and Subaru guy for my non truck needs. If they can really pack all the tech they stated (and functions as stated) this could be a great little motor. Especially tuning it in a “sport style” single or extra cab short bed 2wd. I by no means would expect this thing to move mountains or tow a big rig. But, It has its place, although longevity and reliablity (plus tuning and aftermarket) will be key to its success or demise. Just my two cents...

So, just FYI, I also have a 2016 z71 5.3 AFM crewcab long bed work truck that I have put almost 20k in miles on it driving highway/city, heavy sourthen California traffic, Mountain roads, and some off-roading. I try to max out v4 mode as much as I can to save gas. I have had two dealer oil changes so far and checked the levels. No issues on this truck so far.

There is a TSB about the oil deflector on AFM engine, make sure to note to the dealer that you have noticed the last section of test was performed on highway/afm driving.... Your data seems to suggest the deflector issue, This will help the tech's trace down your oil problem faster! please let us know what the dealer says and the work performed! Keep us posted and keep your spirit up

Then ignore the topic and don't post here. It is what it is. It will never be 100% perfect, deal with it. From the 1st post Now lets get back on topic. Well Put good sir... As with anything there are no 100% answers really avaliable, BUT this topic is useful for a relatively competent mechanically inclined person.(Which I believe there are a few of you on here..) It has the potential to inlighten some to their avaliable options & also help others undertand what's going on with this GTM-900 issue.... Oh and for all you people who post cow patty's like " Its a conspericy... " or "this is a useless" or what ever else BS posted, Shame on you! The pot is calling the kettle black huh?

05gmcz71, that's a low blow for sure and realitivly ignorant statement! Obviously something has happened during engine build or break in to either the rings, lifters or valve guides causing him to leak oil through to cylinders... But it's under warranty and GM will fix it for him! Like MikeNH stated this is a problem that does have 35% or so of people on this Internet site having problems but geuss what? Almost 65% of people on this site DO NOT have this problem...roughly 2/3 are fine! Smiple math dictates that most people are NOT having this problem, even though some of you are! This site is great and all but it by no means represents the total amount of trucks on the road... Most people having trouble will search for validation on why they are having issues, But some one enjoying a smooth running truck and living there life aren't searching the Internet to cry about truck issues on a fourm board... Understand? Oh and MikeNH, don't worry GM will make things right for you because that's a factory made problem, and sad to say Sh*t happens! I have had my gmt-900 almost 5 years now and absolutely love this truck... Tows hard miles & traverses the snow covered roads excellent! Oh yea I burn no oil! :-)

Very useful info, remember that a "thicker" oil does have a harder time making it through rings/valves also can slow down gasket leaks as well... Not a complete fix but can help limp the problem along for many miles! (I know of people using straight 30 weight oil in summer and as high as 20-50w in winter to slow down leaks!) it all depends on how extreme the weather you drive in & how bad the leak/consumption is... And 10-w40 is a realitivly safe "thicker" oil wieght especially in say southern cailfornia & on you higher mileage rig's out there... (50-60k & above) Everyone remember to check for leaks on the engine pan & rear main seal! There are TBS out about different gaskets types that cause oil pan leaks(metal gasket vs rubber gasket) some can even have a faulty pan that will leak only under "driving" conditions, which leaves NO oil puddle in your driveway, BUT still leaking between the engine/trans area as you drive! I had a similar problem years ago... Would not trip the oil light, but would be just a lil low during drain intervals... Some could be suffering from one or all three of the major oil problems found on some of the gtm-900 (AFM normal oil abuse/poor oil quality, faulty or worn rings/lifters/valve guides, or lastly oil pan/rear main oil leaks) any one of those can account for oil loss & if suffering from all three?!? that would drink a whole lot of oil for sure... Lastly, for all of you out there that wait till your idoit light comes on &/or hearing lifters tapping or oil pressure spikes to 0.... Holy crap people!! Check your oil at every gas tank fill up or at least every 500 miles... "Everytime you run your engine that low on oil YOU are doing more & more damge!!!"

QUOTE (Volcom26 @ Mar 14 2011, 10:23 PM) QUOTE (RyanbabZ71 @ Feb 19 2011, 06:22 AM) There are many topics out there and no real data between members. Hopefully this will catch some data and show a real story. Please be thruthful with your selections. Please only post oil consumtion concerns here and please stay on topic. Please no long debates about AFM people either love it or hate it we all understand this. Thanks! 2007 NBS Silverado 1500 z71 with 5.3 AFM (22,000 miles) tow's hard through Cajon/Baker grade(pulling 7k), many mountain trips... NOT using/burning any oil(mobil 1 from the start, now switching to Amsoil) 5w30 always... Truck see's extended freeway towing w/rpms between 3-5k... FYI my Honda Prelude (H22 Vtec) uses at least 1qt per 3000k... Wanna know what Honda thinks? "normal" :-) ------- Why post if you're not using oil, but please vote. The purpose of the poll is to get some data on who, and how many, are using oil and how much per 3k. -------- If you look a couple post's later you will see why I posted on this fourm & and the oil consumption thread, and no offense but I would like to hear you explaination on why some trucks are using oil? Or is your helpful input on this thread asking me why I post? Geez my man, I don't give enough useful info or imput? I would like to see more facts, information & data sharing, not calling out why I am trying to help & impart knownledge to the masses... Especially for those that truly don't understand the tech... Thanks alot buddy!

Upon further investigation of AFM system GM uses in the 5.3/6.0 I have come to a conclusion about why some trucks can consume more oil than say a normal ls1 motor... These new GMT-900's use a system called the "Valve Lifter Oil Manifold" (VLOM) basically it controls the Lifters & Cylinder de-actavtion process by using "oil pressure" to activate & de-active the lifters/valves & certain actions in the manifold, along with PCM cutting injectors & only runs on 1,4,6,7 which also change to a cam lift of .289 (instead of other 4 cyl at .283) This is a beautiful design & impressive when you really understand/comprehend it's complexity yet solid work this system handles... It delivers High output with MPG!! This is very important to understand & due to the extreme abuse this puts on the oil(not including the normal oil duties) and it is very similar to Varaible Valve timing applications like the VVT & Vtec type engines used for 20 years in Imports like Honda/Nissan... With that in mind, "all types" of these engines that have an "oil controlled" variable valve modifying system are all "normal" users of oils... "" Up to 2qts between oil changes!"" This is considered normal, Now this by no means is a perfect system but very beneficial to modern HP and MPG expectations! We all want more of both right? :-) Now here's the tricky part, some people are drinking oil & it's way more than normal... That may be a faulty motor build or maybe poor quality oil, or even worn rings/valve guides... There are many variables that GM has no control over! But If GM messed up on your ride make them fix it do the "consumption test" so they can prove the engine Does or Does NOT fall in between the "normal functions for type of motor" So again in short, I don't burn oil in my 5.3(22k miles) but I may very well or may not... The design of the motor does put me in the "up to 2qt is normal" bracket but guess what? For the balance of HP/MPG I pull out of my finely tuned z71 (almost 26 mpg on the highway!!) I can live with it because I understand the technology... Plus geuss what I stomp that pedel down & I have almost 300whp to move me along quite swiftly when I dont want MPG.... Its the Best of both worlds! I have more to add & will fix the typo's (I'm on my IPhone) All I want is to Stimulate some useful posts & share the facts about GM Trucks with everyone instead of just reading posts like "my truck burns oil I hate GM for that" or " i paid xxxxxx and it uses oil...." Please people lets get some useful, informative INFO on here!! You know? :-)

2007 NBS Silverado 1500 z71 with 5.3 AFM (22,000 miles) tow's hard through Cajon/Baker grade(pulling 7k), many mountain trips... NOT using/burning any oil(mobil 1 from the start, now switching to Amsoil) 5w30 always... Truck see's extended freeway towing w/rpms between 3-5k... FYI my Honda Prelude (H22 Vtec) uses at least 1qt per 3000k... Wanna know what Honda thinks? "normal" :-)