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Old 05-21-2012, 06:36 PM
The PIG Smith's Avatar
The PIG Smith The PIG Smith is offline
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Join Date: Nov 30, 2001
Location: Fort Wayne, Indiana
Posts: 6,525
LS style V4 mode: Active Fuel Management

I recently drove our company's 2008 Chevrolet Tahoe from Butler, Indiana to Pittsburgh, PA.
This Tahoe is powered by a 5.3L V8, model LY5, that was was equipped with Active Fuel Management.
I did not even know what Active Fuel Management was until while driving up the Interstate, the Information Center indicated V4 Mode.
I thought it was some sorta of Variable Valve Timing, but I was wrong.
I looked it up later and as I understand it, the computer shuts of the coil and the injector to 4 cylinders.
Anyways, that Tahoe received economy numbers in the low 20's.
I was greatly surprised that a truck so big and heavy could achieve better than 20 miles per gallon of gas.

I was also shocked at how well this Tahoe drove and rode.
That 5.3 in V8 mode has about 320 horsepower and really had the zip to get up the road! I liked the Vroom Vroom!

OKAY...so you fellows that have performed LS swaps in a FSJ, here is my question to you:
With an 5.3L LY5 with its 4L60E and transfercase (NP241?) can a person get the Active Fuel Management to work in a non GM vehicle?

While doing research, I discovered that on the www.gmfullsize.com forum, folks either love it or hate it.
Well, I can tell you that it worked well for me and I loved it.
I had the power when I wanted and had the economy when I was just cruising.
Seemed to be one of those examples of getting to keep my cake and eating it too!

My hope is that this question will draw a lot of technical discussion.
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Old 05-21-2012, 07:06 PM
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j20owner j20owner is offline
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Join Date: Jan 11, 2003
Location: Kansas City, MO
Posts: 355
Well, where do I start? Can you do it, more than likely. Would I EVER use it? No.

We've had 4 trucks in the last month come in with issues with the lifters. It's not just the coils and injectors that are shut off, it's the lifters for cylinder #1, #4, #6, and #7. The lifters are controlled by oil pressure. There's an AFM Manifold underneath the intake manifold. This is fed pressurized oil by the pump and is equipped with 4 electric solenoids. These solenoids are turned on to allow the pressurized oil to a special passage in the block the the lifter. Once around the lifter, it is fed into a port on the lifter where it enters a channel and presses two locking pins to 'unlock' the lifter. These pins are held out under spring pressure and are what actually allow the lifter to push the pushrod. We've seen these pins stick, causing the lifter to permanently unlock. This of course causes a dead miss. This happened to two of the four trucks. The other two had something break inside the lifter, causing it to be collapsed permanently, also causing a dead miss. In both cases, both heads came off, all the AFM lifters get replaced. Three of the four trucks were under 100,000 miles. The fourth had over 150,000 and the customer decided on a new engine with a warranty of a rebuild.

Glad I could share my experience.
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Old 05-21-2012, 08:54 PM
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billyj7175 billyj7175 is offline
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Join Date: Sep 10, 2001
Location: Sooner State
Posts: 1,513
I can't add anything technical...however, if you do go with the active fuel management, stay with a quiet, stock exhaust. If not, when it activates and shuts down cylinders...it sounds really goofy. My 08' Silverado had it and a 70 series Flowmaster...had more than one person ask "what's wrong with your truck". It was that noticeable.
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