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Can you permanently disable fuel management without setting off trouble codes?

This is a discussion on Can you permanently disable fuel management without setting off trouble codes? within the Performance forums, part of the General Discussion category; Was GM having a wet dream when they came up with this scheme that's supposed to save fuel? I bought ...

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    Can you permanently disable fuel management without setting off trouble codes?


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    Was GM having a wet dream when they came up with this scheme that's supposed to save fuel? I bought a nice exhaust for this thing so I could hear the way a 5.3 should sound ... not to amplify the sound of a castrated V-8 that sounds worse than a real 4banger.

    I honestly don't see how you can make an engine consume less fuel by dragging 4 dead pistons along for the ride. I understand they're not firing, using fuel or building compression, but ... How can making 4 pistons work harder than the other 4 expect to save any fuel?

    I traded in my '06 4x4 Extended cab, standard bed (only 27k on the clock) WITHOUT active fuel management for this '09 with basically same options as my old one and the highway mileage is worse. I knew my '09 wasn't going to be a gas sipper, but my old truck would easily get 18.5 MPG or so on the interstate and this thing can't even come close to touching 17 MPG. I drive like Grandpa Jones on the highway with the cruise set to the speed limit and mileage still suffers. I'm sure this new motor needs to loosen up more since I only have about 2,700 on it, but c'mon! ... not even 17MPG? I broke this thing in hard like I do with every new engine and the crankcase is filled with Amsoil 5W-30 full synthetic. I guess disabling the fuel management isn't as easy as yanking a fuse, right? Thanks for any help.
    2009 5.3 SILVERADO 1500 Z71 Ext. Cab, standard bed -- 4L70e with 3.73 --
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    Born and Raised Chevrolet YenkoST's Avatar
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    Re: Can you permanently disable fuel management without setting off trouble codes?

    You need to get a tune to disable AFM/DOD and no codes will pop up...I've tuned three AFM vehicles with no codes...one of them I personally own.

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    I'm with ya on this one. Traded in my 05 5.3 Reg cab LB 3:73 locker ( with out AFM ) for this 09 5.3 Ext cab 4x4 3:73 locker ( with AFM ) and man is this gas milage sucking. I drive like an old man ( 60 mph on freeways, we live in the country ) and used to get 21 mpg. Now I'm lucky to see 18mpg.
    Last edited by JimRoss; 02-24-2010 at 09:48 PM.
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    Re: Can you permanently disable fuel management without setting off trouble codes?

    Get a tune to get rid of the torque management and the your spark back in order; however, doing that may cause warranty issues. In my 2007 Crew Cab Classic, I'm getting 24.5 at 60mph and 23 at 75 mph but that's with 3.23 gears as well but on 20" wheels. But the tune is spot on....the timing at cruising is only 34 or 36 degrees timing but that's where I've seen the biggest mpg...any higher and my mpg goes to crap.
    Last edited by YenkoST; 02-25-2010 at 07:10 AM.

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    but the newer trucks are better for the environment

    Used to own a FSC, now I just have my extremely old Buick.
    Have some perspective please. Thank you.

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    Quote Originally Posted by JimRoss View Post
    I'm with ya on this one. Traded in my 05 5.3 Reg cab LB 3:73 locker ( with out AFM ) for this 09 5.3 Ext cab 4x4 3:73 locker ( with AFM ) and man is this gas milage sucking. I drive like an old man ( 60 mph on freeways, we live in the country ) and used to get 21 mpg. Now I'm lucky to see 18mpg.
    Yeah ... I feel your pain, at least you're getting an extra mpg that I'm not. I knew AFM was a crock of **** when I bought this truck, but you can't get them without it and I couldn't pass up the 0% financing. Plus I now have a warranty again and they gave me almost what I owed on my old truck. If it weren't for that I would've kept my '06 and fixed the tiny bit of cancer starting on the door bottoms ... that was the only thing wrong with it. The crappy mileage (and bogus AFM) is my only gripe about this new one. I do have to say this thing rides sooooo much better than the old torsion bars in the '06 ... night/day difference. I'm sure the mileage will improve in time so I'll just ride it out and try not to bitch too much for now, lol.

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    Quote Originally Posted by YenkoST View Post
    Get a tune to get rid of the torque management and the your spark back in order; however, doing that may cause warranty issues. In my 2007 Crew Cab Classic, I'm getting 24.5 at 60mph and 23 at 75 mph but that's with 3.23 gears as well but on 20" wheels. But the tune is spot on....the timing at cruising is only 34 or 36 degrees timing but that's where I've seen the biggest mpg...any higher and my mpg goes to crap.
    That's my main concern about a custom tune. I'm sure most of these tuners know what they're doing with your computer, but I'm still nervous about the idea. It just bs that we spend all this $ on a new truck and they're not delivered from the factory running at full potential and you have to pay somebody else more cash to get them running the way they SHOULD'VE been in the first place. Warranty companies are a bigger scam than the tree huggers that concocted AFM so I'm all for bending them over provided you don't get caught.

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    AFM does improve fuel mileage, not sure what vehicle you are driving that the mileage isn't improved over a comparable truck without it.
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    Re: Can you permanently disable fuel management without setting off trouble codes?

    Quote Originally Posted by Joe View Post
    AFM does improve fuel mileage, not sure what vehicle you are driving that the mileage isn't improved over a comparable truck without it.
    Maybe it does for some people, but not me. All my info was in the very first post if you missed it. I'm not trying to start a feud or anything, but show me some real world data to back your claim (other than GM's fudged numbers), then I might start to believe. IMO, There's waaaay too many variables involved trying to obtain accurate results to prove you or I of being wrong. Sure, AFM probably does help someone who lives in Texas (which is most likely where they get their #s from), but here in Pa. my AFM hardly comes into play in the first place. I'm just going by my experience with this truck compared to my old truck driving the same exact routes with the same exact driving habits. Like I already mentioned above, my new truck is barely broke in with only 2,700 miles opposed to 27,000 that were on the '06 so I can't even begin to really compare the two accurately until I add another 0 on the end of the new one's clock. Call me stubborn or old-school if you like, but you'll never be able to sell me the brainstorm that AFM is actually THAT beneficial to everyone. I personally believe it's just another ploy for GM to make more money because there sure are a ton of people bitching about the mileage. Have you ever come across anyone who said "Wow!! This AFM is awesome, I can can pass 50 more gas pumps down the road compared to my old non-AFM truck!!" .... I haven't.

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    Quote Originally Posted by ImperialBlueZ71 View Post
    Maybe it does for some people, but not me. All my info was in the very first post if you missed it. I'm not trying to start a feud or anything, but show me some real world data to back your claim (other than GM's fudged numbers), then I might start to believe. IMO, There's waaaay too many variables involved trying to obtain accurate results to prove you or I of being wrong. Sure, AFM probably does help someone who lives in Texas (which is most likely where they get their #s from), but here in Pa. my AFM hardly comes into play in the first place. I'm just going by my experience with this truck compared to my old truck driving the same exact routes with the same exact driving habits. Like I already mentioned above, my new truck is barely broke in with only 2,700 miles opposed to 27,000 that were on the '06 so I can't even begin to really compare the two accurately until I add another 0 on the end of the new one's clock. Call me stubborn or old-school if you like, but you'll never be able to sell me the brainstorm that AFM is actually THAT beneficial to everyone. I personally believe it's just another ploy for GM to make more money because there sure are a ton of people bitching about the mileage. Have you ever come across anyone who said "Wow!! This AFM is awesome, I can can pass 50 more gas pumps down the road compared to my old non-AFM truck!!" .... I haven't.
    I understand your frustration, but you are comparing apples and oranges when comparing a 2006 GMT 800 and a 2009 GMT900 trucks fuel economy.
    Just imagine the 2009 GMT 900 truck without AFM, mileage will be even worse.

    The mileage is worse in the newer trucks for a few reasons, 1 of them being weight. Your comparison would be valid if you compared a 2009 truck WITH AFM to a 2009 truck with AFM disabled.

    These engines aren't fully broken in for at least 7,000-8,000 miles.

    Quote Originally Posted by ImperialBlueZ71 View Post
    How can making 4 pistons work harder than the other 4 expect to save any fuel?
    Because 4 of them arent getting fuel anymore. Think of a 3000 lb 4 cylinder Mustang and a 2500 lb 5.0l V8 Mustang cruising along, variables equalled. Which will use less fuel?
    Without any compression being built, the only losses are from the dead cylinders rings on the cylinder and the wristpin and con rod bearing and MINOR pumping losses. It's not a stretch IMO to see why AFM works because it does indeed save fuel.


    Why did you sell the 06? Sounds like a cherry truck.

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    Quote Originally Posted by YenkoST View Post
    Get a tune to get rid of the torque management and the your spark back in order; however, doing that may cause warranty issues. In my 2007 Crew Cab Classic, I'm getting 24.5 at 60mph and 23 at 75 mph but that's with 3.23 gears as well but on 20" wheels. But the tune is spot on....the timing at cruising is only 34 or 36 degrees timing but that's where I've seen the biggest mpg...any higher and my mpg goes to crap.
    20" rims OK, but what height are your tires? I can see mileage being better with a 3.42 than a 3.23 if these GEN3/4 engines that make peak torque @ 4000-4400rpm are forced to cruise along the highway at 1500rpm.

    Just trying to find out what rpm you are turning at 75mph?

    In my L31 when it was new, with 3.08's (stock 27" tires) best fuele conomy was had over 70 mph. These newer truck certainy run quite a bit taller tires, which is why the got rid of the 3.08 option in the GMT800/900 trucks.

    peace
    PAuly
    97 GMC 2wd RCSB 5.7, s10 2700 footstall, Hooker 24621hkr LT's , 2.5" cats dual 4"pipes exit B4 pass. side tire, custom driveshaft 3.42 G80 FIPK MAF descreen GM/Mercruiser Marine intake manifold 29lb LS2(EV6) injectors Ed Wright PCM(best mod), LT4 KM 14.8@94mph 2.007 4000lbs 122mph

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    My 4.3L 98 K1500 gets 19/25MPG according to the window sheet from the dealer, my parents 09 Sierra gets 19-26 according to it's window sheet.

    It's crazy that a ECSB Z71 w/5.3L V8 which has 125HP more than my truck can get equal to better MPG than my RCLB 4.3L can.


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    Re: Can you permanently disable fuel management without setting off trouble codes?

    [QUOTE=Pauly;4620042]I understand your frustration, but you are comparing apples and oranges when comparing a 2006 GMT 800 and a 2009 GMT900 trucks fuel economy.
    Just imagine the 2009 GMT 900 truck without AFM, mileage will be even worse.

    The mileage is worse in the newer trucks for a few reasons, 1 of them being weight. Your comparison would be valid if you compared a 2009 truck WITH AFM to a 2009 truck with AFM disabled.

    These engines aren't fully broken in for at least 7,000-8,000 miles.


    I knew I wasn't being totally fair about my comparison and to be honest I forgot all about the weight difference ... that alone is a MAJOR factor. As you know I'm just a little pissed about the mileage, but I'm sure it will (I hope) in time get better with more miles.

    Because 4 of them arent getting fuel anymore. Think of a 3000 lb 4 cylinder Mustang and a 2500 lb 5.0l V8 Mustang cruising along, variables equalled. Which will use less fuel?
    Without any compression being built, the only losses are from the dead cylinders rings on the cylinder and the wristpin and con rod bearing and MINOR pumping losses. It's not a stretch IMO to see why AFM works because it does indeed save fuel.


    I knew everything you mentioned here as I already stated previously at the top, but I'm still not exactly fond of the system and how it works. I'm still having a hard time swallowing the whole idea ... that's just me. Why did you sell the 06? Sounds like a cherry truck.
    Yes, the 06 was really nice (even the dealer couldn't believe what nice shape it was in) except for very minor rust starting on some of the door bottoms on the inside. I always take excellent care of my stuff and it payed off since they gave me $18k for it and I still owed $20k to pay it off. I bought it used with 20k on the clock and drove it for a year so basically I paid $2 grand to drive it for a year.

    What did me in was driving a new 2010 with the 5.3 and 6 spd. tranny ... I loved it! Those 2 extra gears really seemed to give it a little more punch than my 06 had and gave me a hard-on for a new one. Here's the downer .... I couldn't swing the payments for the 10 so I had to settle for my 09 with the 4 spd to get the 0% deal, but I don't regret it at all. Getting rid of that torsion bar susp. in the old truck makes my new one feel like a Caddy. I like this truck as much (if not more) than the 06 so all is good in my book. Other than the touchy climate control and mileage in this one I have no major complaints ... I just have to learn to be patient and ride it out for a while.


    I
    Last edited by ImperialBlueZ71; 02-25-2010 at 06:08 PM.
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    Re: Can you permanently disable fuel management without setting off trouble codes?

    i know in the dod L99 engine; in order to totaly remove the dod, its a tune, cam swap, and i think something else. just something to chew on.
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    Re: Can you permanently disable fuel management without setting off trouble codes?

    Quote Originally Posted by Pauly View Post
    20" rims OK, but what height are your tires? I can see mileage being better with a 3.42 than a 3.23 if these GEN3/4 engines that make peak torque @ 4000-4400rpm are forced to cruise along the highway at 1500rpm.

    Just trying to find out what rpm you are turning at 75mph?

    In my L31 when it was new, with 3.08's (stock 27" tires) best fuele conomy was had over 70 mph. These newer truck certainy run quite a bit taller tires, which is why the got rid of the 3.08 option in the GMT800/900 trucks.

    peace
    PAuly
    3.23 gears with P275/55R20 tires on GM SS Silverado 20" wheels cruising at 75mph at 1850rpms. Just posting my numbers for others...not starting a war. My old 2002 ext cab Z71 truck with 3.73 gears and 30.5 tires on 16" wheels got 20.3 mpg on the hwy at 72mph crusing at 2000 rpms for more comparison.

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    Re: Can you permanently disable fuel management without setting off trouble codes?

    I wouldn't get in any big panic to see a huge mileage increase in time. The whole 7000-8000 miles thing is BS. There is nothing in a modern roller cam engine that takes 7000 miles to set in. Your rings will fully seat in less than 500 miles of use and then it's all over, probably after the first 20 minutes of running if you are driving so it's under load. I am pretty sure GM doesn't include any special tuning sets that are time based either. The tuning on these late model trucks sucks the big one from day one and stays that way until you have it improved....... of course voiding all warranty in the process. I guess you can try the PCM/TCM swap idea as you have a 4 speed still and probably get away with it. Us with the trucks with the 6 speed can't really do that since the TCM is in the valve body in the transmission now. Couple that to a harsh 2/3 shift that my 6 speed always has ( but the dealer can't replicate of course, even though there is a TSB for it, but only for trucks older than my 09) and I wouldn't try it. I really don't want to have to tow it to a tuner to reflash it to stock after it piles up. Probably still get voided though as the computer would show it had just been flashed. I am just no longer purchasing late model stuff as this is just getting worse. Pretty soon you have 500 Hp ratings and 18 second quarter miles while getting 10 mpg. Exaggeration, yes, but it seems to be headed that direction. Maybe all the automakers should go bankrupt for building pathetic performing product.

    Case in point for mileage. I drive a 2009 2500HD extended 6.5" bed 4X4 with the LY6 6.0 litre and the 6L90E/ 3.73 gears. I did a mileage test that ended before the truck had 1000 kms on it, or 620 miles. I got 14 mpg imperial. For fun I just did it again recently and nothing has changed except the truck has 20000 miles or 30000 kms on it. Guess what.......... 14 mpg imperial...........
    Both fair comparos as they were both highway mileage tests. I accumulate a ton of miles in short periods of time as this is a company provided work truck.
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    I hate GMT900 trucks period.

 

 

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