Disable Fuel Management System?

Cnadianff · March 20, 2019

With my mods the main one being 37 inch tires should I disable my FMS? I notice the only time I can get the truck to switch to 4 cyl mode is down hill or on a flat with steady pressure no acceleration.

Am i seeing any benefit? Is it harmful to the engine to always be in and out of modes on the flat?

Thanks

Mikebtte · March 20, 2019

It is simply in place as GMs attempt to look like they are trying to save fuel. Having the system cycle can in no way be good on the torque converter, transmission, U-joints, lifters ext. It is not designed to last but to be a way of making you think your saving fuel. I have ran mine for 100K miles ON and 50K OFF and my fuel mileage is better with it off and the life of the engine is extended for having it OFF.

I am not running 37'' tires, but I have towed with the Fuel Management turned ON, It was not very nice and created a lot of unnecessary surging. Turn it off and you will thank yourself later. My opinion...

Wiggums · March 20, 2019

I've read that the gas mileage would hardly be affected with the active fuel management. I have dynamic fuel management which is supposedly better and goes all the way down to 2 cylinders but I don't think it's really making an impact on my gas mileage. Just a hunch here, don't take my word for it.

Sierra Dan · March 20, 2019

FMS ?

You mean AFM (Active Fuel Management) ?

Cnadianff · March 20, 2019

20 minutes ago, Sierra Dan said:

FMS ?

You mean AFM (Active Fuel Management) ?

Yes AFM. Thanks Sierra Dan

Jacoby · March 21, 2019

Turn it off

Sierra Dan · March 21, 2019

16 hours ago, Cnadianff said:

Yes AFM. Thanks Sierra Dan

TXGREEK · March 21, 2019

I've read that the gas mileage would hardly be affected with the active fuel management. I have dynamic fuel management which is supposedly better and goes all the way down to 2 cylinders but I don't think it's really making an impact on my gas mileage. Just a hunch here, don't take my word for it.

I turned mine off on my 2018 6.2 and have noticed a more responsive engine. Approx .50-1.0 mpg difference but it’s a 6.2 designed to give more smiles per mile [emoji6]

Sent from above

Wiggums · March 21, 2019

You mentioned it's more responsive. I've gotten a few lags even with the stop/start being off and I suspect it could be the "dynamic" fuel management as it is called right now.

If I'm getting 25 mpg, I can live with that.

GMCShack · March 21, 2019

I have DFM on my 2019 and cannot tell the difference in gas mileage but it seems more responsive with it turned off, but mostly I turn it off for any around town driving for the thought of saving wear and tear as Mikebtte was talking about above, and not that concerned about what small amount of gas I may or may not be saving or using. Just my opinion and of course YMMV. ;)

mitchely03 · March 21, 2019

My trucks tuned now with AFM off, but when it was untuned with AFM it was still such a better driving truck than with it ON. I saw no immediate loss with MPG.

3tspapat · March 21, 2019

it really depends on the type of driving you are doing. As stated before, I am typically driving around town and it does not save me more than 0.5 miles per gallon. While in V4, I've noticed that the motor staying in V4 and struggling to pull up a small grade and watching the MPG bar go down before kicking into V8 and watching the bar go back up. I have the eAssist so it does use the some e-power to try and keep the vehicle in V4 longer. I'm sure this is why my MPG isn't much better in with AFM.

On flats or downhill that is when the V4 does well (no brainer).

BlackBearPerf · March 21, 2019

21 hours ago, Cnadianff said:

With my mods the main one being 37 inch tires should I disable my FMS? I notice the only time I can get the truck to switch to 4 cyl mode is down hill or on a flat with steady pressure no acceleration.

Am i seeing any benefit? Is it harmful to the engine to always be in and out of modes on the flat?

Thanks

The 07-13 models with AFM had the major issues, oil consumption, lifter failures. AFM is typically a fuel saver on the 2014+ models, so we would only suggest disabling it if you have heavy wheels/tires or can't tolerate the sound with your exhaust. It really is a personal preference on the newer vehicles, how it feels to you, what you are experiencing, if you want to disable it or not.