Some questions that have been bugging me about DOD...

[I12XLR8]

OK. First, what does DOD stand for? Is this the same as AFM (please define this as well).

Next, how does DOD work and how does getting rid of it add power.

When does DOD or AFM (assuming they are the same thing) work on the vehicle? Is it engine speed that determines when it will kick in? Will it kick in at any engine speed as long as there is little to no load on the engine?

I am toying with a cam in the 1-2 year future of the car but like that when I cruise I have some fuel savings with the DOD. However, I think my 3.70 gear have negated the DOD so changing the cam should be less of a hit on the fuel bill (over what I am current paying). My understanding of this technology is weak I don't want to make any assumptions.

Help?

[Cobra]

DOD and AFM are the same thing. Displacement on Demand and Active Fuel Management. Others can chime in but I believe it kicks in when cruising at certain speeds. Most likely highway speeds. Not sure what the MPH or RPM has to be in order for it to be activated.

Others that have done a DOD (Cam) swap have reported better gas mileage while others report a loss of 1-2 mpg.

[zemog255]

DOD stands for displacement on demand. It works based off of engine load and rpm. I'm not sure what speeds it comes in on, I never paid attention usually just at crusing speeds. You can access engeneering mode and see when it is coming on and off.

You don't necessairly gain power by deleting the DOD. The stock DOD cam is tiny thats why the gains are so big from a simple cam swap in these cars.

They do make DOD cams but I haven't seen much on them. If you really want to keep it. Most resonable street cam setups won't hurt you gas mileage alot. Don't expect to gain any but a mpg or 2 loss is to be expected maybe more in the city. Really has to do with who is tuning the car. Hope this helps you some.

[LDM]

If you want some technical info:

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.

Valve Lifter Oil Manifold Assembly



The valve lifter oil manifold assembly (1) 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 (2). Each solenoid directs the flow of pressurized engine oil to the active fuel management intake and exhaust valve lifters (5). The active fuel management oil pressure relief valve (6), 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 (4) is located in the valve lifter oil manifold oil inlet passage. The oil pressure sensor (3) 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 (1) travels upward and downward to actuate the rocker arm and valve. The spring loaded locking pins (5) of the lifter are extended outward and mechanically lock the pin housing (4) to the outer body of the valve lifter (3).

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 (6) of the valve lifter.

When operating in V4 mode, pressurized oil forces the locking pins (11) inward. The pushrod (7) remains in a constant position and does not travel upward and downward. The outer body of the lifter (9) moves upward and downward independently from the pin housing (10). The valve lifter spring (8) 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.

Engine Block



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 (2) in the rear of the cylinder block. Cylinders 1, 4, 6, and 7 each have 2 vertical, cast-in-block oil passages (1). The vertical oil passages permit oil flow from the manifold assembly to the valve lifter bores.

Engine Control Module (ECM)

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

[I12XLR8]

This is an awesome resource to understand how the system works...thank you very much, LDM! It answers most of my questions but I am still left with the important one.

I am still trying to find out when it will activate and more importantly when it will not. The closest information to this is "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." Is there an RPM ceiling that will prevent DOD from activating if crossed? I only care about DOD on the highway but as I am cruising at 2400rpm now I'm not sure it is on at all.

zeemog255 mentioned engineering mode as a way to determine whether DOD was engaged. From what I remember is seemed to only tell me that AFM was enabled, not that is was currently being used or not. I will give it a try later today if possible but would still like more info if there's any out there to be had.

[SRG963]

I believe it depends on throttle position and engine load. I am probably wrong on the percentage, but lets say anything over 20% throttle position will not allow AFM to engage.

I've had AFM active above 85mph.

Your DIC should tell you if AFM is engaged or not, and you can also check out your throttle position.

[I12XLR8]

I've had AFM active above 85mph.

Did you know this by feel or through Engineering Mode?

[SRG963]

Did you know this by feel or through Engineering Mode?

Both

[Matt@Texas-Speed]

It's more about load than MPH....if you're doing 80-mph on an incline, it's not going to shut down cylinders. But 80mph downhill and you have a great chance of doing so! From the factory, it is tuned fairly conservatively and will not go into 4 cylinder mode with much load at all. With a little tuning though, you could turn your G8 into a real mileage getter on the highway, without giving up anything in town or on the street at lower speeds.

I'm "thrifty" enough that we tuned my 2007 Silverado 5.3L for mileage...between tweaking the A/F and timing, DFCO, and AFM we were able to make it mileage very well. I got about 20-21mpg in town (cruise control when I could, even at low speeds), and about 26mpg on the highway at 70mph without any major climbs or descents.

[TomPierce]

PM me your email address and I will send you a screen shot. It's too big to upload or attach, but it shows all the DOD settings for a stock G8 GT.