Active Fuel Management

**Restlessone** · 02-28-2009, 05:14 PM

I was wondering what the opinion of the group on GM active fuel management. Is this system reliable, it seems very complicated.? Could it be disconnected and the truck still run ie pulling a fuse or something.
Obviously I don't understand the system so I look forward to your commrents

**TRPLXL2** · 02-28-2009, 06:46 PM

I don't know a thing about the active management system either, but I do know it switches from 8 cylinders down to 4 cylinders. My personal opinion is the dealership can't even fix a traditional fuel injection system, so how the hell are they going to keep up with this stuff. I have heard the speech a hundred times from the ASE certified technicians, "They send us to school all the time to keep up with all of the upcoming technology." Well how can you move on to rocket science when you haven't even completed biology, the concept of it is awesome but how does it really perform. Thank you for asking this question, I am curious about some of the answers that will pop up............AMY

**Restlessone** · 02-28-2009, 08:13 PM

Yeah it seems you know about as much as I do. I was hoping with the fountain of knowledge on this site someone would jump in.

**Restlessone** · 03-01-2009, 10:37 AM

No response, I'm shocked.
I'm really just trying to find out if this is a reliable system. When the warranty runs out will you have to replace expensive solenoids. There must be somebody out there with this system on there trucks.

**DrewsZ71** · 03-01-2009, 11:13 AM

I have the AFM on my truck. Ive had it over a year now and it seems to work flawlessly. I havent had any problems with it. If you drive on flat roads and highways, it'll will save you some MPGs. I live in a hilly area so it only cuts down to 4cyl mode when im on flat spots or coming down hill. Theres been several times ive done 70-75 mph on the freeway in 4cyl mode getting 36mpg. The changing from 4cyl to V8 mode is seemless there is no harsh bumping or jarring whenver it changes. I like mine, I could still live without it buts its just a lil bonus for me i guess...lol

**Dickie** · 03-01-2009, 11:14 AM

I have it on my truck havent had any problems with it yet knock on wood....Mine dont kick down to often with the way I drive

**Restlessone** · 03-01-2009, 10:12 PM

Thanks for the replies. One more question, can you adjust the system or turn it on/off.

Thanks

**chance** · 03-01-2009, 10:28 PM

Why would you want to turn it off, Its designed to save you money?!? The system is actually more simple then you are thinking and Im pretty sure it is mostly controled by the engines computer simply turning off the injecters and cuting the ignition to the 4 cylinders (no expensive solinoids). I also believe that throttle position, and vehicle speed determine whether the AFM is operating or not.

just my .02 cents

**Steve** · 03-01-2009, 10:45 PM

You can easily turn the system on and off, with your foot on the accellerator.

I've driven multiple different Silverados with the AFM in them and it's very impressive to watch it work.

The system is only moderately complicated and GM tried to do it in the early 80's but the computer technology wasn't advanced enough to handle it. The engine has been redesigned to allow for exhaust valve to stay closed when the computer determinds that there is a low demand on the engine. That essentially keep pressure inside the value and then the next rotation the intake valve is kept from opening as well. The gas pressure inside acts like a gas spring essentially.

All this sounds like it's complex, but it's really just 1) shutting off the fuel, 2) shutting down the exhaust value, 3) shutting down the intake valve. Then when power is needed, the exhaust value opens up, followed by the regular cycle of the engine. I think they started upgrading the engine with some type of solinoid system now to make this all work and only like half of the cylanders can be deactivated at any one time.

**chance** · 03-02-2009, 12:03 AM

i did a quick search, i found this on wikipedia. i know its not an officail site but it supports what was previously stated by steve and corrects what i had thought.

In order to deactivate a cylinder, the exhaust valve is prevented from opening after the power stroke and the exhaust gas charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the intake valve is prevented from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring. As multiple cylinders are shut off at a time (cylinders 1, 4, 6 and 7 for a V8), the power required for compression of the exhaust gas in one cylinder is countered by the decompression of retained exhaust gas in another. When more power is called for, the exhaust valve is reactivated and the old exhaust gas expelled during the exhaust stroke. The intake valve is likewise reactivated and normal engine operation is resumed. The net effect of cylinder deactivation is an improvement in fuel economy and likewise a reduction in exhaust emissions. General Motors was the first to modify existing, production engines to enable cylinder deactivation, with the introduction of the Cadillac L62 "V8-6-4" in 1981.