Active Fuel Management

[lonestarnox]

You "gearheads" reading this thread, please help. I'm very interested in how the Active Fuel Management is working out, specifically on the 5.3L W-bodies. My local dealer is offering me an excellent deal on his last Monte Carlo SS...but I'm not sure. I was a victim of the V-8-6-4 Caddy deal back in '81 (yeah I'm old). I understand technology has come a long way etc. etc. Can the AFM be deactivated? Bypassed? Chip replacement available? Or does it work so well I need not be bothered? Any and all comments and suggestions appreciated.

[shadams]

Cylinder Deactivation (Active Fuel Management) System Description

To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the cylinder deactivation system ON to deactivate engine cylinders 1 and 7 on the left bank, and cylinders 4 and 6 on the right bank, switching to a V4 mode. The engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications.

When commanded ON, the ECM will determine what cylinder is firing, and begin deactivation on the next closest deactivated cylinder in firing order sequence. The Gen IV engine has a firing order of 1-8-7-2-6-5-4-3. If cylinder number 1 is on its combustion event when cylinder deactivation is commanded ON, the next cylinder in the firing order sequence that can be deactivated is cylinder number 7. If cylinder number 5 is on its combustion event when cylinder deactivation is commanded ON, then the next cylinder in the firing order sequence that can be deactivated is cylinder number 4.

Cylinder deactivation is accomplished by not allowing the intake and exhaust valves to open on the selected cylinders by using special valve lifters. The deactivation lifters contain spring loaded locking pins that connect the internal pin housing of the lifter to the outer housing. The pin housing contains the lifter plunger and pushrod seat which interfaces with the pushrod. The outer housing contacts the camshaft lobe through a roller. During V8 mode, the locking pins are pushed outward by spring force, locking the pin housing and outer housing together causing the lifter to function as a normal lifter. When V4 mode is commanded ON, the locking pins are pushed inward with engine oil pressure directed from the valve lifter oil manifold (VLOM) assembly solenoids. When the lifter pin housing is unlocked from the outer housing, the internal pin housing will remain stationary, while the outer housing will move with the profile of the camshaft lobe, which results in the valve remaining closed. One VLOM solenoid controls both the intake and exhaust valves for each deactivating cylinder. There are 2 distinct oil passages going to each cylinder deactivation lifter bore, one for the hydraulic lash-adjusting feature of the lifter, and one for controlling the locking pins used for cylinder deactivation.

Although both intake and exhaust valve lifters are controlled by the same solenoid in the VLOM, the intake and exhaust valves do not become deactivated at the same time. Cylinder deactivation is timed so that the cylinder is on an intake event. During an intake event, the intake cam lobe is pushing the valve lifter upwards to open the intake valve against the force of the valve spring. The force exerted by the valve spring is acting on the side of the lifter locking pins, preventing them from moving until the intake valve has closed. When the intake valve lifter reaches the base circle of the camshaft lobe, the valve spring force is reduced, allowing the locking pins to move, deactivating the intake valve. However, when cylinder deactivation is commanded ON, the exhaust valve for the deactivated cylinder is in the closed position, allowing the locking pins on the valve lifter to move immediately, and deactivate the exhaust valve.

By deactivating the exhaust valve first, this allows the capture of a burnt air/fuel charge or exhaust gas charge in the combustion chamber. The capture of exhaust gases in the combustion chamber will contribute to a reduction in oil consumption, noise and vibration levels, and exhaust emissions when operating in V4 mode. During the transition from V8 to V4 mode, the fuel injectors will be turned OFF on the deactivated cylinders. The ignition system secondary voltage or spark is still present across the spark plug electrodes on the deactivated cylinders. If all enabling conditions are met and maintained for cylinder deactivation operation, the ECM calibrations will limit cylinder deactivation to a cycle time of 10 minutes in V4 mode, and then return to V8 mode for 1 minute.

Switching between V8 and V4 mode is accomplished in less than 250 milliseconds, making the transitions seamless and transparent to the vehicle operator. The 250 milliseconds includes the time for the ECM to sequence the transitions, the response time for the VLOM solenoids to energize, and the time for the valve lifters to deactivate, all within 2 revolutions of the engine crankshaft.

The cylinder deactivation system consists of the following components:

• The VLOM assembly

• Eight special valve lifters, 2 per deactivating cylinder

• The engine oil pressure regulator valve for cylinder deactivation operation

• Gen IV cylinder deactivation engine block

• The ECM

Valve Lifter Oil Manifold (VLOM) Assembly
The cylinder deactivation system uses an electro-hydraulic actuator device called the valve lifter oil manifold (VLOM) assembly. The VLOM is bolted to the top of the engine valley, below the intake manifold assembly. The VLOM consists of 4 electrically operated Normally Closed Solenoids. Each solenoid controls the application of engine oil pressure to the intake and exhaust valve lifters on the cylinders selected to deactivate. Engine oil pressure is routed to the VLOM assembly from a passage on the rear of the cylinder block.

All 4 VLOM solenoids are connected in parallel to a fused ignition 1 voltage circuit, supplied by the powertrain relay. The ground or control circuit for each solenoid is connected to the engine control module (ECM).

When all enabling conditions are met for cylinder deactivation, the ECM will ground each solenoid control circuit in firing order sequence, allowing current to flow through the solenoid windings. With the coil windings energized, the solenoid valve opens, redirecting engine oil pressure through the VLOM into 8 separate vertical passages in the engine lifter valley. The 8 vertical passages, 2 per cylinder, are connected 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 control circuit for the solenoids, allowing the solenoid valves to close. With the solenoid valves closed, engine oil pressure in the control ports is exhausted through the body of the solenoids into the engine block lifter valley. The housing of the VLOM incorporates several bleeds in the oil passages to purge any air trapped in the VLOM or engine block.

To control any contamination to the hydraulic circuits, a small replaceable oil screen is located in the VLOM oil inlet passage, below the oil pressure sensor. The oil pressure sensor is a 3-wire sensor which provides oil pressure information to the ECM.

During service, use extreme care in keeping the VLOM assembly free of any contamination or foreign material.

Engine Control Module (ECM)
The engine control module (ECM) is responsible for the management and control of all engine functions. Each ECM comes equipped with a specific set of software/calibrations designed for that engine and vehicle application. The ECM will determine engine operating parameters, based upon information from a network of switches, sensors, modules and communication with other controllers located throughout vehicle. Internal to the ECM is an integrated circuit device called a low-side driver. The low-side driver is designed to operate internally, like an electronic switch. An individual low-side driver controls each valve lifter oil manifold (VLOM) solenoid. When enabling conditions for V4 mode are met, the ECM will command the low-side driver to ground each VLOM solenoid control circuit, in firing order sequence. Internal to the low-side driver is a fault detection circuit, which monitors the solenoid control circuit for an incorrect voltage level. If an incorrect voltage level, such as an open, high resistance, or short to ground, is detected, the low-side driver, along with the fault detection circuit, will communicate the condition to the central processor in the ECM. The ECM will then command a return to V8 mode, set a corresponding DTC, and illuminate the malfunction indicator lamp (MIL) on the instrument panel.

Cylinder Deactivation Inhibit Reasons
Listed below are the powertrain conditions that will inhibit V4 mode, while operating under light load driving conditions:

• Engine manifold vacuum low

• Brake booster vacuum pressure low

• Accelerator pedal position rate of increase too high, electronic throttle control

• Accelerator pedal position too high, electronic throttle control

• Ignition voltage out of range

• Engine oil pressure out of range

• Engine oil temperature out of range

• Engine RPM out of range

• Transmission gear incorrect

• Transmission range incorrect

• Transmission gear shift in progress

• All cylinders activated via scan tool output control

• Minimum time in V8 mode not met

• Maximum V4 mode time exceeded

• Engine oil aeration present

• Decel fuel cutoff active

• Fuel shut-off timer active

• Minimum heater temp low, HVAC system

• Reduced engine power active, electronic throttle control

• Brake torque management active

• Axle torque limiting active

• Engine metal over temperature protection active

• Catalytic converter over temperature protection active

• Piston protection active, knock detected

• Hot coolant mode active

• Engine over speed protection active

• Fault Active or Fault Pending--cylinder deactivation is disabled for the following faults:

- Brake Booster Vacuum Sensor

- Manifold Absolute Pressure Sensor

- Engine Oil Pressure Sensor

- Engine Coolant Temperature Sensor

- Vehicle Speed Sensor

- Crankshaft Position Sensor

- Engine Misfire Detected

- Cylinder Deactivation Solenoid Driver Circuit

The scan tool output control is used to deactivate half of the engine cylinders, V4 mode, by commanding all of the solenoids ON, or deactivate one cylinder switching to a V7 mode, by commanding ON one solenoid. Listed below are the powertrain conditions that will inhibit V4 mode, or V7 mode, with the engine running, while using the scan tool output control function:

• Engine speed out of range

• Manifold absolute pressure (MAP) sensor fault

• Accelerator pedal position too high, electronic throttle control

• Piston protection active, knock detected

• Engine oil temperature out of range

• Engine oil pressure out of range

• Engine oil aeration present

• Engine metal over temperature protection active

• Accelerator pedal position rate of increase too high, electronic throttle control

• Cylinder deactivation solenoid driver circuit fault

• Engine coolant temperature sensor fault

• Catalytic converter over temperature protection active

• Brake booster vacuum pressure low

• Brake Booster Vacuum Pressure Sensor Fault

• Axle torque limiting active

• Brake torque management active

• Vehicle speed sensor fault

• Engine coolant temperature too high

• Engine not running

• Vehicle speed not zero

• Engine coolant temperature low

• Reduced Engine Power Active, electronic throttle control

• Transmission gear incorrect

• Transmission range incorrect

• Ignition voltage out of range

• Maximum V4 mode time exceeded

Listed below are the powertrain conditions that will inhibit a cylinder deactivation solenoid from being energized, with the ignition ON and the engine OFF, while using the scan tool output control function:

• Engine speed not zero

• Vehicle speed not zero

• Transmission not in park or neutral

• Ignition voltage out of range


Lots of info for sure, but I have had 0 cars/trucks in here with AFM problems, and its been out for 3 yrs now, started on the 05 Envoy V8's. So, as you can see its fairly complex, but again, it has proven thus far to be trouble free.

[Smaart Aas Saabr]

One of the problems with the V864 was that the controller wasn't nearly powerful enough and the software on it was poorly done (perhaps at the limit of what the controller could do). The PCM on the AFM cars is much much more powerful and also it has only 2 choices not three which is a big difference.

[69Chevy]

It's been out for a while in it's current configuration and I've yet to see any problems at all come through the shop door. I say go for it!

[zabolots]

33k miles and not a single problem on my '05 GXP.

[Triple-X08]

havent seen any issues yet with the 5.3 AFM system, seen a few 3.9 v6's with the system and it has a voltage regulator problem.

the only issue you will have with that car is the tire pressure monitor. new impalas and monte carlos have problems with them.


the 5.3 is a good engine, and it has alot of torque. i have owned a few monte carlos, i love them.

[01cavalier]

The AFM system has been trouble free, haven't heard many complaints about normal operation either.
The information mentions a maximum amount of time in V4 mode, how long can it run in that mode? It also mentions a minimum time in V8 mode, any information on that?

[1999 White C5 Coupe]

Originally Posted by Triple-X08

havent seen any issues yet with the 5.3 AFM system, seen a few 3.9 v6's with the system and it has a voltage regulator problem.

the only issue you will have with that car is the tire pressure monitor. new impalas and monte carlos have problems with them.


the 5.3 is a good engine, and it has alot of torque. i have owned a few monte carlos, i love them.

Tell me more - I am considering ordering a 2008 Impala with the 3.9 V6 with active fuel management (and stability control - the option I was waiting for).

[rbarrios]

SOME of the EARLY 3.9L engines with AFM- had an issue that appears when in 3 cylinder mode. This has been corrected.
Early build 07's - owners report that when in 3 cyl mode- headlights and dash lights sort of pulsate. Some say its noticeable- others say annoying. I never saw it myself- but they described that it was apparent to them (no one ever said it appeared to bother oncoming traffic- so it may have only been noticeable to driver).
Within the past month or so- a fix was put out. Owners take the car in and the fix is applied. No more pulsating. A coil is repalced and a ground strap is installed I believe.
I have an 07 3.9L Impala built Feb 12, 07. the problem NEVER appeared to us. (the keyless entry and tire monitor problem) also never appeared on our car. I talked to another owner whose Impala was built a few days before mine.... no problems there either. So the problem has been fixed.

[1999 White C5 Coupe]

Originally Posted by rbarrios

SOME of the EARLY 3.9L engines with AFM- had an issue that appears when in 3 cylinder mode. This has been corrected.
Early build 07's - owners report that when in 3 cyl mode- headlights and dash lights sort of pulsate. Some say its noticeable- others say annoying. I never saw it myself- but they described that it was apparent to them (no one ever said it appeared to bother oncoming traffic- so it may have only been noticeable to driver).
Within the past month or so- a fix was put out. Owners take the car in and the fix is applied. No more pulsating. A coil is repalced and a ground strap is installed I believe.
I have an 07 3.9L Impala built Feb 12, 07. the problem NEVER appeared to us. (the keyless entry and tire monitor problem) also never appeared on our car. I talked to another owner whose Impala was built a few days before mine.... no problems there either. So the problem has been fixed.

Thanks for the reply.

[WannabeRich]

Originally Posted by rbarrios

SOME of the EARLY 3.9L engines with AFM- had an issue that appears when in 3 cylinder mode. This has been corrected.
Early build 07's - owners report that when in 3 cyl mode- headlights and dash lights sort of pulsate. Some say its noticeable- others say annoying. I never saw it myself- but they described that it was apparent to them (no one ever said it appeared to bother oncoming traffic- so it may have only been noticeable to driver).
Within the past month or so- a fix was put out. Owners take the car in and the fix is applied. No more pulsating. A coil is repalced and a ground strap is installed I believe.
I have an 07 3.9L Impala built Feb 12, 07. the problem NEVER appeared to us. (the keyless entry and tire monitor problem) also never appeared on our car. I talked to another owner whose Impala was built a few days before mine.... no problems there either. So the problem has been fixed.

Apparently, my Impala LTZ was an early 07 with the AFM/headlight problem (bought in Dec 06). My dealer did the fix and no longer an issue. Also had the tire pressure monitor problem which was fixed at the same time. First reported both problems in Jan 07. Took GM five months to come up with a solution.

[ggcurtis]

I can not believe what I'm hearing, I have a 2007 silverado that has been in the shop 3 times due to what feels like a misfire but no check engine light. Had the service manager drive and he said we had a problem but when the head mechanic connected to the ECM and drove it down the road with me he showed me that tremendous jerk I was feeling was the cylinder activating. They have had several complants on this and have contacted GM engineers on this one due to all the vehicles having the updated software loaded.

[69Chevy]

Originally Posted by ggcurtis

I can not believe what I'm hearing, I have a 2007 silverado that has been in the shop 3 times due to what feels like a misfire but no check engine light. Had the service manager drive and he said we had a problem but when the head mechanic connected to the ECM and drove it down the road with me he showed me that tremendous jerk I was feeling was the cylinder activating. They have had several complants on this and have contacted GM engineers on this one due to all the vehicles having the updated software loaded.

We've sold a lot of GMT900 with AFM and as I say I've yet to see anyone come through our door with an AFM problem. The few I've driven that had gone into and out of 4 cylinder mode have been seemless. Maybe there's something related to the area where you live? Just a guess, don't know. That's kinda strange.

EDIT: Byt the way- welcome to GMI!

[vitonvalve]

Great info. How can you turn it off?

[rbarrios]

i think ive read some post in other forums, where getting a tune, can turn off AFM