Pulling DFM fuses

[03blackz71]

18 hours ago, Firehawk99 said:

Well I tried this and my truck ran like crap! It was shifting all wonky and started hard. I put them back in and it's back to normal. I have a 21 6.2 trail boss.

 

I think the fuse numbers are for the 5.3l.     The 6.2l might be different.

 

 

[WeGone]

1 hour ago, 03blackz71 said:

 

I think the fuse numbers are for the 5.3l.     The 6.2l might be different.

 

 

 

Can anyone confirm on 6.2?

[Silverado4x4]

19 minutes ago, WeGone said:

 

Can anyone confirm on 6.2?

Nope same fuse numbers. If you're unsure the fuse numbers are in the back part of your owner's manual.

Edited December 21, 2021 by Silverado4x4

[JohnH4260]

The images below are from pages 352-354 in my 2021 GMC Sierra owners manual. In the engine compartment fuse box, it shows #60 and #67 are the Active Fuel Management 1 and Active Fuel Management 2 fuses. Maybe there’s another system involved as well. 

[kmeleon]

I hooked up to my Bluetooth scan tool yesterday and I cannot see anyway to monitor how many cylinders are active in real time. I do believe pulling the fuses works but I have no way of proving it. 

[RedLT]

On 12/19/2021 at 3:42 PM, voided3 said:

Driving in L7 on the 8-speed or L9 on the 10-speed does disable DFM on the L84 5.3 or L87 6.2 with DFM.

 

Driving in L8 on the 8-speed or L10 on the 10-speed, however, does not; you have to lock out the final overdrive gear to disable it. Driving in L8 or L10 is the same as D on these trucks.

Sorry if it's a dumb question but what does driving in L7 do? The truck only shifts gears 1 through 7? Is DFM beneficial when traveling long distance and disable DFM (L7) when driving around town?

[WeGone]

Its my understanding As long as your driving in one gear under the highest you have using L? the cylinder cancellation does not activate. I use L9 under 70mph.

[voided3]

On 12/28/2021 at 10:51 AM, RedLT said:

Sorry if it's a dumb question but what does driving in L7 do? The truck only shifts gears 1 through 7? Is DFM beneficial when traveling long distance and disable DFM (L7) when driving around town?

Correct, using "L" limits your gear range. If you have L1 through L7 selected, DFM is disabled. If you are driving in D or L8, DFM is active. I drive in L7 all of the time, but our highway speed limits are only 55-65 around here. Our truck with the 3.23 rear end turns 1900 RPM at 65 MPH in 7th gear and I still squeak out 19 to 20 MPG on the highway.

[RedLT]

Thanks for the explanations fellas!

[BlancoSilverado]

I might try this in the next few days,

I do have a scan tool that tells me if the DFM is activated and which cylinders they are activated. I will also post any codes that become present. 

[WeGone]

1 hour ago, BlancoSilverado said:

I might try this in the next few days,

I do have a scan tool that tells me if the DFM is activated and which cylinders they are activated. I will also post any codes that become present. 

 

looking forward to the results.

[Firehawk99]

20 minutes ago, WeGone said:

 

looking forward to the results.

Me too. I'd be willing to try again.

[kmeleon]

8 hours ago, BlancoSilverado said:

I might try this in the next few days,

I do have a scan tool that tells me if the DFM is activated and which cylinders they are activated. I will also post any codes that become present. 

Please do! Nobody has been able to know for sure if this works. I'd like to know 100%

[Diamond817]

Anybody with an aftermarket exhaust or a muffler delete would be able to verify if this works within 2 minutes of driving after pulling these fuses.

[kmeleon]

Well hopefully someone comes along that can prove/disprove it soon. My fuses have been out for over a week with no drivability issues.