Chevy Silverado and GMC Sierra Forum banner

AFM V8/V4 Mode

116K views 147 replies 51 participants last post by  Monkey Wrench 
#1 ·
Is there a way to turn off the AFM system with a programer or tune? I just put a flowmaster on my truck and can hear and feel the switching between modes and it starting to get on my nerves! The truck also feels slugish switching out of V4 mode.
 
#3 ·
If you have the 6 speed auto, you can also run in 4th or 5th (manual mode) around town, and it will not go into V4. But yes, most tuners can turn it off.
 
#4 ·
Dude I know what your feeling, I could not stand that AFM noise and shudder!
It really amplified when I threw a lift and 35's on!
So I just got a Hypertech Max Energy and turned that crap off.
Its your best bet man, you get better power and milage and their not too expensive. Go to autoanything.com.
 
#5 ·
Yep turned mine off with my Intune tuner actually gets better mileage off mine sounded like a diesel in v four mode with my dual exhaust much better now
 
#6 ·
Do you think that will effect the factory warranty in the event of a non AFM related issue should one arrise? Seems I read somewhere it would but have no way to verify.
 
#7 ·
GM would have to prove that turning off the AFM was specifically what caused a failure. Otherwise they cannot void your warranty. Having the AFM off will not cause brake, suspension, drivetrain, etc type of failures. Now if there was an internal failure in your engine, they may claim it was due to the fact you "tinkered" with the engine. But, they would have to prove it....and I doubt they could.
Also, remember, AFM is not a mechanical process. Its all done electronically. Your vehicles computer is simply shutting off fuel flow and shutting down the spark to those cylinders. By turning AFM off, all you are really doing is telling the computer to operate "normally" all of the time, and to not use a feature. I cannot see where there could be a mechanical problem related to turning off the AFM.
 
#8 ·
The reading I have done regarding AFM:

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.

Compliments of another truck site.

LGSONE
 
#9 ·
I stand corrected. I did some "research" (via Google) and found the same things as LGSONE posted. So it is both mechanical and electronic. But still, I don't see how it could void a warranty by NOT using the function.
 
#10 ·
I thought is was as you stated EK but when at the speed shop I was "enlighted". Those guys HATE the AFM.

LGSONE
 
#12 ·
Th only thing that I could see is that by tuning the ECM to turn off the DOD there could be issues with gunk/sludge stuck on the mechanical parts of the AFM system by not being used. Maybe I'm wrong here but that's the only thing I could see.
 
#13 ·
FYI..........................................

Service Information
Home Publications Number Search New Bulletins Bulletin Search Feedback Help

Document ID: 2439286
#09-06-04-026B: Identifying Non-GM (Aftermarket) Engine and Transmission Calibrations for V8 Gas Engines Using Tech 2 or Global Diagnostic System (GDS) - (Apr 7, 2010)

Subject: Identifying Non-GM (Aftermarket) Engine and Transmission Calibrations for V8 Gas Engines Using Tech 2® or Global Diagnostic System (GDS)

Models: 2006-2010 GM Passenger Cars and Light Duty Trucks (Excluding Saab 9-7X)
2006-2009 HUMMER H2
2006-2010 HUMMER H3
Equipped with V8 Gas Powered Engines Only

Attention: This bulletin applies to V8 gas powered engines ONLY. For Duramax™ diesel powered engines, refer to Corporate Bulletin Number 08-06-04-006G.

This bulletin is being revised to add the 2010 model year and information about retrieving calibrations on a Global A vehicle. Please discard Corporate Bulletin Number 09-06-04-026A (Section 06 - Engine/Propulsion System).

General Motors is identifying an increasing number of engine, transmission and catalytic converter part failures that are the result of non-GM (aftermarket) engine and transmission control calibrations being used.

When alteration to the GM-released engine or transmission control calibrations occurs, it subjects powertrain and driveline components (engine , transmission, transfer case, driveshaft and rear axle) to stresses that were not tested by General Motors. It is because of these unknown stresses, and the potential to alter reliability, durability and emissions performance, that GM has adopted a policy that prevents any UNAUTHORIZED dealer warranty claim submissions to any remaining warranty coverage, to the powertrain and driveline components whenever the presence of a non-GM (aftermarket) calibration is confirmed - even if the non-GM control module calibration is subsequently removed.

Warranty coverage is based on the equipment and calibrations that were released on the vehicle at time of sale, or subsequently updated by GM. That's because GM testing and validation matches the calibration to a host of criteria that is essential to assure reliability, durability and emissions performance over the life of the warranty coverage and beyond. Stresses resulting from calibrations different from those tested and released by GM can damage or weaken components, leading to poor performance and or shortened life.

Additionally, non-GM (aftermarket) issued engine control modifications often do not meet the same emissions performance standards as GM issued calibrations. Depending on state statutes, individuals who install engine control module calibrations that put the vehicle outside the parameters of emissions certification standards may be subject to fines and/or penalties.

This bulletin outlines a procedure to identify the presence of non-GM (aftermarket) calibrations. GM recommends performing this check whenever a hard part failure is seen on internal engine or transmission components, or before an engine assembly or transmission assembly is being replaced under warranty. It is also recommended that the engine calibration verification procedure be performed whenever diagnostics indicate that catalytic converter replacement is indicated.

The PQC has a process to confirm the ECM/PCM calibration is GM issued. The PQC will require a picture of the engine calibration verification screen, as outlined in this bulletin, before authorizing any V8 gas powered engine replacement.

If a non-GM calibration is found and verification has taken place through GM, the remaining powertrain and driveline warranty will be blocked and notated in GMVIS and the dealership will be notified. This block prevents any UNAUTHORIZED warranty claim submission.

Deleted technical info pertaining to validation etc

Suspected Tampering or Vehicle Modifications

0.2 hr

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
 
#14 ·
Whoa, it looks like they can see it. Just to be safe and keep $$ in my pocket from warranty repairs, I'm staying stock until my PT is out, but that's just me :|
 
#15 ·
Me too. I am not that annoyed by it, and I can just drop to "M5" to override it around town anyway.
 
#17 ·
part of the technical stuff I deleted says they have the ability to count the number of events that took place so its sounds like anytime the system is accessed, it leaves a trail.

Note: GDS is capable of displaying up to 10 Calibration History events.
23. Select: Calibration History from the drop down menu in order to display the following items on the screen:
• Calibration History Buffer
• Number of Calibration History Events Stored
• Calibration Part Number History
• Calibration Verification Number History
24. Select: Screenshot.
If you want to read the whole thing, I found a copy HERE

Looks like the new GDS (Global Diagnostic System) is going to be pretty tough to fool when it comes to tunes . The screen shot of the software shows a history graph of the last 10 calibrations with the part numbers and amount of times it has been flashed . No more tech 2 CVN's .....now they will be using laptops with MDI interfaces.
 
#18 ·
There is a way to mask these events, it is not appropriate IMHO to post it but if you do the google research it is doable. From a discussion I had with some "GM" folks it comes down to this. If a type of failure occurs that is considered out of the normal operational issues documented they will sometimes be requested to do the verification. If a failure occurs that is documented and does not reek of abuse it is just repaired. Dealers have to protect themselves and if they do a repair and it is later verified that it should not have been done, they eat it... well. I have personal relationships with several owners of dealerships, been my clients for years, and while they did not get into specifics they are monitored by GM and held accountable. And once a claim is denied they are scrutinized much more. The dealer I work with for my truck is very accommodating but not to a point they would create liability for themselves.

LGSONE
 
#19 ·
Sounds like a catch 22 here to some degree. The primary concern I have with the AFM sysytem is the statistical probability of developing an excessive oil consumption issue that could require replacement of pistons and rings ultimately. I certainly wouldn't want to think that I am reluctant to disable the AFM for fear of loss of warranty coverage when leaving it active may very well lead to the need for engine warranty work. The whole thing is a big can of worms.
 
#22 ·
GoAudio said:
lets see if i read this right it turns off the same 4 cylinders every time it goes into 4 cyl mode???? meaning it wears the other 4 unevenly...hmmmmm i'd rather have all 8 running the same then 4 running more then others.
This is my concern. I plan on driving this truck for a long damn time. I don't want issues at 101k but i dont want to loose coverage before that either.......
 
#26 ·
Correct. Fuel delivery, and spark are stopped. The pistons are still moving. So wear should be about the same.

I believe there are a lot of 5.3l engines with AFM on the road that have high mileage.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top