Why was AFM disabled to begin with? Was it a problem and failed then had to be disabled?
Or was it disabled because we just don't like the idea of coasting using only 4 cylinders?
I have been trying to understand this commonly discussed issue since I found this forum.
Engine Half@$$ was a bad idea to start with, even if GM had spared no expense on the V4 mode parts so that they'd outlast the full time V8 parts.
Attacking "don't like the idea of coasting using only 4 cylinders", because I've a particularly unique experience with it that others ought to learn from.
Had my ecm tuned in 2013 to INCREASE both the likelihood of V4 Mode AND length of its duty cycles when in effect, which was a huge mistake -
only so much can be done to improve the fuel economy of a 5900lb vehicle, but me and my tuner tried (it was a lease).
Anytime my '12 Yukon XL SLT was in 3rd 4th 5th or 6th / +21MpH, under light load & TPS% meaning lazy driving, the Engine Half@$$ed to TRY to save gas. TRY.
For what it's worth my tuner (see my sig) did a great job, whenever I even considered fun, it was already in V8 mode (and it'd already downshifted too),
but most of the time I spend driving for uber/lyft/juno/gett/via, I was in V4 mode TRYING to save gas. Basically, it worked for about 1.5-2 years.
After that, MpG started to go down. After about 2.5-3 years, MpG was worse than prior to the ecm tune, despite me trying to drive even more conservatively.
In 2016, oil consumption hit at least 1Qt every 1000 miles if not more - part-time cylinders were sucking oil past their rings into those combustion chambers.
Despite changing the oil every 2500-3000 miles (monthly) with Group4 synthetic, the problem I'm talking about in this post regarding Engine Half@$$
is that the part-time V4 cools down and warms up & cools down chronically, while the full-time V4 keeps a far more steady temp.
Unfortunately the full-time V4 can only do so much to keep the part-time V4 warm,
ask Chrysler about engine blocks that cleaved/shattered from staying in V4 mode too long.
My tuner and I were aware of this, so we limited how long V4 mode would stay in effect in any one instance, but it was longer than GM OE.
The long-term result of V4 mode, even if you manage to avoid all the other potential component failures that have been documented by thousands,
is that the part-time V4 wears out sooner than the full-time V4. The longer the engine lasts, the worse the fuel economy gets, both in V4 mode and in V8 mode,
because the full-time V4 is dragging the other 4 lazy worn out cylinders. Turns out I wore out sooner than anyone elses without intending to,
but every other engine that has not yet disabled Engine Half@$$ will eventually age out the same way, even if the lazy cylinders don't carbon up like mine did.
This post is NOT about lifter failures / slipping or bent pushrods / rocker failures / cam lobe wear, or even TCC wear eventually taking out the 6L80E.
Tens of thousands of posts out there about those.
My '12 Y-XL SLT never experienced ANY of those failure modes. Still should've disabled Engine Half@$$ first chance I got. Everyone else too.
www.tahoeyukonforum.com
