Why No Afm ?

[Eddie 70]

Last Sunday I took a 250 mile trip in my 07. When I got closer to my destination, the AFM quit kicking in. The last 70 miles or so were between 45 and 65 MPH. The closer to the destination, the less often the AFM would come on. Is there anything any reason that the AFM should not continue to work? The engine temps and trans temps all seemed normal. As a matter of fact trans temps had dropped for the last part of the trip compared to the interstate driving.

 

Anything ideas about the AFM. I did manage to get 18.0 MPG out of the truck for the trip though.

[cerbomark]

if it s like my 09 it will only kick in while in the highest gear. (which is 6th for me). If it s under any type of load, such as hills or added weight it won t go into 4 mode. Maybe you had it locked out of OD? By the way, I had mine turned off on my 2007 and again on my 2009. It did nothing for my mileage.

[Eddie 70]

Thanks for the reply Mark. It just seemed to go away completely near the end of the trip is what is puzzling me. I have no idea if my truck was going into OD during those times but, I was off the gas and it still didn't kick in.

[rogerf]

Check your tow/haul switch. Remember reading AFM gets locked out while in tow mode. It is very odd to not have AFM cycle. Mine is very sensitive to any added load (A/C, grades, weight, headwinds, speed, etc...) but this is odd.

[nathan60]

a f m stiil works in tow haul mode believe me been there done that..

[pm26]

a f m stiil works in tow haul mode believe me been there done that..

 

I verified that when I test drove a 2008 truck with the 5.3 liter engine.

[L76PWRD]

I don't care for AFM, I'm actually going to look into removing the AFM system.

[C. Charles Hahn]

As I recall correctly, the factory parameters for AFM disable it if certain parameters such as speed, gear, trans temp, and coolant temp are met. Perhaps something just got warm or your foot got heavier toward the end of the trip?

[ColoradoSkiCountry]

I've found with my old 07 5.3 that going up the slightest of hill would cause it to go back into 8 CYL mode. Even the slightest of hill. Of course, there is no flat land out here in Colorado unless you go east far enough.

[saxdogg]

Were you driving with a tailwind and downhill under 65mph? That's the only time mine turns on...

[Eddie 70]

Tomorrow afternoon, I make the 250 mile trip back home. When I get home, I am going to check the trans fluid and make sure it is back where it is supposed to be. Its been a while since I have checked an auto trans, still check it with warm fluid in park, idling? My last DD was a manual.

 

I will update the thread with what happens with the AFM. The last 10 miles are mostly coming down a long grade.

[Eddie 70]

I checked the fluid this morning after driving 10 miles to work. Fluid level was in the area between cold and hot levels, so I took that as good. Started the 250 mile trip home and kept an eye on AFM activity. Seems the hotter the trans the less active AFM is. The highest I ever saw trans temp was around 176 or so with outside temps around 96. Closer to my house and 230 miles later the outside temp was around 85 and the trans temps had dropped to around 160. AFM seemed to be coming on more often and staying around longer.

 

Is there a tutorial about what makes AFM function? I guess I need to get out there and scan my truck with HP Tuners and see what I can see there too. I just wish I knew enough about HP Tuners to do some real good with it. I bought it for the 70 LS conversion and have never really played that much with it.

[Ryan00TJ]

Is there a tutorial about what makes AFM function? I guess I need to get out there and scan my truck with HP Tuners and see what I can see there too. I just wish I knew enough about HP Tuners to do some real good with it. I bought it for the 70 LS conversion and have never really played that much with it.

 

 

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

[Yz2k20]

Once I've noticed that my AFM stopped working on my way to work one morning. On the way home that afternoon, everything was back to normal. Strange..

[Eddie 70]

Mine seemed to work correctly on the way back home but I thought it was due in part to the high temps outside. It is supposed to be very warm on Sunday going back so I will see what happens this time.