School Me On How Afm Works.

[2016 Sierra Owner]

Hello All, I have been wondering how this AFM works and how the lifters are failing. I have worked on large diesel trucks before. Some have Jake breaks on the engine that work by cutting oil flow to the lifters. This in turn makes the lifter soft (for lack of a better word) and it does not allow the push rod to open the exhaust valve thus the piston has to push the exhaust through the valves slowing the engine down acting as a break. Is this kind of how it works on the AFM system? Reason I am asking is when I get my Black Bear tune in the next few days. I want to turn the AFM system off. Once it is turned off the lifters should be ok since they would not be starved for oil any more or are the AFM lifters different from regular lifters and are just prone to fail?

[MS3DALE]

Cylinder Deactivation (Active Fuel Management) System Description

System Operation

General Motors Active Fuel Management engine control system has the ability, under certain light load driving conditions, to provide maximum fuel economy by deactivating 4 of the engines 8 cylinders. The engine will normally operate on 8 cylinders in V8 mode during starting, idling, and medium or heavy throttle conditions. When commanded ON, the engine control module (ECM) will direct the active fuel management system and deactivate cylinders 1 and 7 on the left bank and cylinders 4 and 6 on the right bank, forcing V4 mode. Refer to Lubrication Description and Cylinder Deactivation (Active Fuel Management) System Description.

 

Valve Lifter Oil Manifold Assembly

 

The valve lifter oil manifold assembly is bolted to the top of the engine block beneath the intake manifold assembly. The oil manifold consists of 4 electrically operated and normally-closed solenoids. Each solenoid directs the flow of pressurized engine oil to the active fuel management intake and exhaust valve lifters. The active fuel management oil pressure relief valve, located in the oil pan, regulates engine oil pressure to the lubrication system and the oil manifold.

 

When enabling conditions are met for active fuel management operation, the ECM will ground each solenoid control circuit in firing order sequence, allowing current to flow through the solenoid windings. With the windings energized, the solenoid valves open and direct pressurized engine oil through the valve lifter oil manifold into 8 vertical passages in the engine block lifter valley. The 8 vertical passages, 2 per cylinder, direct pressurized oil to the valve lifter bores of the cylinders to be deactivated. When vehicle operating conditions require a return to V8 mode, the ECM will turn OFF the ground circuit for the solenoids, allowing the solenoid valves to close. When the solenoid valves are closed, remaining oil pressure is exhausted through the bleed passages of the valve lifter oil manifold into the engine block lifter valley. The housing of the oil manifold incorporates several oil bleed passages that continually purge trapped air from the manifold and engine block.

 

To help control contamination within the active fuel management hydraulic system, a small replaceable oil filter is located in the valve lifter oil manifold oil inlet passage. The oil pressure sensor monitors engine oil pressure and provides information to the ECM.

 

Active Fuel Management Valve Lifters

 

When operating in V8 mode, the active fuel management valve lifters function similar to the non-active fuel management valve lifters. The active fuel management oil manifold solenoids are in the closed position, with no pressurized oil directed to the valve lifters. The pushrod travels upward and downward to actuate the rocker arm and valve. The spring loaded locking pins of the lifter are extended outward and mechanically lock the pin housing to the outer body of the valve lifter.

 

When the active fuel management system is commanded ON, the ECM will direct the solenoids of the oil manifold to open and direct pressurized oil to the valve lifters. Oil travels through the valve lifter oil manifold and engine block oil galleries and enters the inlet port of the valve lifter.

 

When operating in V4 mode, pressurized oil forces the locking pins inward. The pushrod remains in a constant position and does not travel upward and downward. The outer body of the lifter moves upward and downward independently from the pin housing. The valve lifter spring retains tension on the valve train components to eliminate valve train noise.

 

When the active fuel management system is commanded OFF, the ECM directs the solenoids of the oil manifold to close, stopping the flow of pressurized oil to the valve lifters. The oil pressure within the lifter will decrease and the locking pins will move outward to mechanically lock the pin housing and outer body.

 

The active fuel management engine block incorporates additional features to support active fuel management system operation. Engine oil pressure is routed to the valve lifter oil manifold assembly from an oil gallery in the rear of the cylinder block. Cylinders 1, 4, 6, and 7 each have 2 vertical, cast-in-block oil passages . The vertical oil passages permit oil flow from the manifold assembly to the valve lifter bores.

[peteking]

^^^ Yeah...what he said!

[MS3DALE]

^^^ Yeah...what he said!

Now you don't think I typed all of that do you?

 

 

 

 

[2016 Sierra Owner]

You did'nt type all of that?? By the way Thanks for the reply!

[[email protected]]

Some of that is even over my head. Or maybe I just didn't understand it. But, that's a hell of a concept to grasp, probably doesn't save much gas, imo.

[jro909]

afm dosen't work....oh my i've created a monster

[cerbomark]

afm dosen't work....oh my i've created a monster

like many of us I had afm turned off through tuning on my last two gmt900 s.

[MaverickZ71]

How AFM Works:

1. Read GM brochure telling how AFM gives you great fuel mileage. Watch YouTube videos of Howie Long and Jim Rome telling you the same.

2. Purchase GM truck with window sticker saying you'll get at least 1-2 mpg better than Ford/Dodge/Toyota. False advertising.

3. Drive new GM truck. Notice how, even with 6 speed transmission, it feels like it needs 3.73 or shorter gears and a BlackBear tune, since the GM tune is only focused on fuel mileage.

4. Figure your mileage on a few tanks of fuel with a calculator. Notice how the DIC is always overoptimistic by 1 or 2 mpg and 1 or 2 gallons used. More false advertising.

5. Read posts at GM-Trucks.com and anxiously wait for the cloud of blue smoke at startup, oil consumption problems (1 qt. in 2000 miles is normal, ARE YOU KIDDING ME?), or lifter rattles to signify that you are not one of the few blessed owners, but rather one of the growing masses with problems.

6. Take truck to GM dealer, TSB in hand so they can't say they can't find it, and pray that they do a good job fixing it.

7. Pray that the new AFM lifters hang in there long enough for you to trade the truck in on a non-AFM model at another dealer (since that dealer knows your truck has problems).

8. Watch to see if these millions of ticking time bombs (pun intended) take Government Motors down for the 2nd and final time.

[DanS]

Any pointers to the direction of the TSB on this?

 

How about a litre or so over 5000kms? Is this a little more acceptable?

[seamonster]

I have a 07 6.0 with 4:10's and my AFM works great.

It seems to do what it was inteded to do.

If I dont drive my truck for week or so it will clatter on start up-----should I be worrying about this?

I love this truck, it has tons of power---pulls my 7Klbs trailer great.

But I only have 10K miles on it, should I plan on trading it soon?

[pm26]

I have a 07 6.0 with 4:10's and my AFM works great.

It seems to do what it was inteded to do.

If I dont drive my truck for week or so it will clatter on start up-----should I be worrying about this?

I love this truck, it has tons of power---pulls my 7Klbs trailer great.

But I only have 10K miles on it, should I plan on trading it soon?

 

That's why your AFM works great - so far.

[pm26]

Any pointers to the direction of the TSB on this?

 

How about a litre or so over 5000kms? Is this a little more acceptable?

 

If your engine has 200,000 km on it, yes.

[jrrod2004]

thanks for putting me to sleep with the read Rich...

[MaverickZ71]

thanks for putting me to sleep with the read Rich...

 

 

Gotta love those TSBs! ZZZZZZZZZZZZZZzzzzzzzzzzzzzzzzz