Cylinder Deactivation Update

Just so you guys know with regards to the CD "feature". Mazda released a new service alert for the 2.5 with CD. They have been replacing the cylinder head(with new modified one) in cars that have failures due to CD. This was released after the recall and is a fairly recent development. Obviously there's been troubles even after the recall
 
Impressed that MAZDA stepped up to permanently fix the issue with a problem engine. I always felt that adjusting the oil pressure was a bandade fix and that a clip or another method to secure the rocker to the cam was the best way. CD doesn't suck, only the engineering design was flawed. Ed
 
Strange that there haven't been any reports on problems after the original recall, but we are a small group after all. Happy to see Mazda step up. yrwei52 will be happy :)

I wonder if Mazda just did the software/firmware update as a holdover until they could gather the resources/parts for this service alert.

I'll update the original post to include this new info.
 
Impressed that MAZDA stepped up to permanently fix the issue with a problem engine. I always felt that adjusting the oil pressure was a bandade fix and that a clip or another method to secure the rocker to the cam was the best way. CD doesn't suck, only the engineering design was flawed. Ed
Although I personally dislike the concept of cylinder deactivation and would never want one, but I believe this Service Alert SA-058/20 from Mazda doesn’t mention anything about physical changes on cylinder head assembly. Rather, the SA merely describes:

DESCRIPTION
A new cylinder head assembly for service parts has been newly established for SKYACTIV-G 2.5 with cylinder deactivation when replacement is needed. Valves, valve springs, valve spring seats, and cotters (IN/EX) are included in the new assembly.


In other words, in USA only, any repair job which requires cylinder head replacement now can only order 0000-99-SCX5 Cylinder Head Set Kit, which includes many necessary gaskets、washers、bolts、and clips, instead of old PYY4-10-SJ0 Cylinder Head Set. Also there’s a note in the SA which seems to indicate this new 0000-99-SCX5 Cylinder Head Set Kit is fully assembled and Mazda dealer should charge less labor time for cylinder head replacement:

NOTE: DO NOT USE the cylinder head replacement labor time listed in Warranty Wizard. That labor time is for a bare head and includes time to swap parts from the original head to the new head.

For an already efficient 4-cylinder engine implementing a very complicate cylinder deactivation which requires many changes to engine and transmission to fight against vibration, and all of these efforts are for only 0~1 mpg gain on EPA ratings. The history on CD has proven the long-term reliability issues on fouling spark plugs、misfire、oil consumption、engine mounts、and even engine wear. In addition to thermal complication between active and inactive cylinders which causes many side-effects, sudden deactivating a cylinder and shutIng off its injector which “causes formation of pressure pulses inside the common rail, which is harmful”. Yes, I believe CD does suck!
 
I don’t think there were any changes or improvement to the original design though. I could be wrong though: “cotters” could be the improvement. When people experienced the rocker arm fall off, Mazda was replacing the entire engine as a fix. Rather than continuing that action, this looks like the new approved repair: a replacement head. Much cheaper and labor intensive than a full engine swap.
 
What "CD display" are you referring to. I am not aware of any display, and in fact asked my dealer over a year ago if there was a display I hadn't yet discovered. At least on my '18 model there is no display to indicate when the CD kicks in.
The following comments apply to a US 2020 2.5L gasoline normally aspirated. The experience of others may vary.

Real time cylinder deactivation can displayed on the touch screen at Applications > Fuel Economy Monitor. You will not find this anywhere in the 714 pages of the PDF owners manual.

If you want to use the touch screen for something else, a handy alternative would be to set the right instrument pod to the "Info" setting that shows real time mpgs. For example, in a recent test in normal (not sport) mode, I found that after accelerating to 50 mph and then easying off the throttle or holding it steady, the real time mpg monitor might jump up to 45-55 mpgs and the cylinder deactivation display shows two cylinders running. Then, taking my foot all the way off the gas pedel, the real time mpg needle buries at 80 and zero cylinders are shown to be active on the touch screen. At low speed, around 15 mph, I've found two cylinder mode tops out in the the low 40's mpg range; all the way off the gas again buries at 80. I never use sport mode so others may or may not see differences.

The long and short is if you use the real time mpg monitor, any jump into the 40s or above would tell you cylinders are shutting down; buried at 80 tells you all 4 are shut down.

I find the cylinder deactivation/reactivation in this model to be entirely transparent with no noticeable change in engine noise, vibration, nothin'.
I think you're confusing engine auto stop/start (engine cuts off when you pull to a stop, then starts again when you take your foot off the brake) with cylinder deactivation. CD on GM and Mazda vehicles is pretty much unnoticeable (I have worked for both brands). Auto stop/start though is very noticeable on GM vehicles
At full stop idle in drive the cylinder deactivation display in the above referenced year and model shows all 4 cylinders running without exception in my brief tests. That's different from other makes that tout cylinder deactivation or shut down/restart at idle. That's a good thing. Constant reignitions from full stop idle can't be anything but additional wear and tear on the motor and starter.

In fact, I've found all 4 cylinders running under all conditions up to 10 mph which suggests Mazda wants to be primed for get up and go without any lag or unusual noise or whatnot, keeping the process transparent.

Some confusions may arise from Mazda's use of the term "Stop and Go" for something entirely different.
 
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When people experienced the rocker arm fall off, Mazda was replacing the entire engine as a fix. Rather than continuing that action, this looks like the new approved repair: a replacement head. Much cheaper and labor intensive than a full engine swap.

You may be right. This does make a lot of sense.
 
Wow, well this doesn’t make me feel good about my recent purchase of a 2020 GT.

The lack of VIN specification indicates 2020s did not get the new head.

Such a dumb move by Mazda, just for the small percentage in fleet mileage.

You have a GT Reserve, don't you? The service alert only applies to Skyactiv-G 2.5 engines with Cylinder Deactivation.
 
19 Reserve and a 20 GT

Oh sorry, my mistake. But if yrwei52 and ruthrj are correct, it's not actually a "new" head, it's just been established as a separate assembly. This way, if the head needs to be replaced, they can just order the head assembly instead of ordering and replacing the whole engine.
 
This may mean that for folks who didn't get the recall, and get the failure the recall was meant to prevent, instead of getting a new engine, you might get a new cylinder head.
 
At full stop idle in drive the cylinder deactivation display in the above referenced year and model shows all 4 cylinders running without exception in my brief tests. That's different from other makes that tout cylinder deactivation or shut down/restart at idle. That's a good thing. Constant reignitions from full stop idle can't be anything but additional wear and tear on the motor and starter.

In fact, I've found all 4 cylinders running under all conditions up to 10 mph which suggests Mazda wants to be primed for get up and go without any lag or unusual noise or whatnot, keeping the process transparent.

At 2,000 RPM, a piston moves up and down 25 times per second. In a four-stroke engine, a combustion event occurs once every 40 milliseconds at this speed. The engine can switch between 4 and 2 cylinders in less than one engine revolution. For all practical purposes, the engine can switch from 2 to 4 cylinders instantly - it's not a gradual "ramp", but rather a sudden event.

I've never heard of an engine with cylinder deactivation technology running on a reduced number of cylinders at idle. Can you give me an example of one that does that I may have missed?

The primary reason the engine runs on all cylinders at low engine speeds (including idle) is because it would shake your teeth out running on 2 cylinders. :)
 
At 2,000 RPM, a piston moves up and down 25 times per second. In a four-stroke engine, a combustion event occurs once every 40 milliseconds at this speed. The engine can switch between 4 and 2 cylinders in less than one engine revolution. For all practical purposes, the engine can switch from 2 to 4 cylinders instantly - it's not a gradual "ramp", but rather a sudden event.

I've never heard of an engine with cylinder deactivation technology running on a reduced number of cylinders at idle. Can you give me an example of one that does that I may have missed?

The primary reason the engine runs on all cylinders at low engine speeds (including idle) is because it would shake your teeth out running on 2 cylinders. :)
I'll trust you on the 2-cylinder business though as I noted if you let off the gas into coast somewhere between 10 and 15 mph dropping to low RPMs it goes to 2-cylinder mode with no teeth rattling, then giving it gas it switches to 4-cylinder, seamless throughout from my experience.

If reaction times are that twitchy, why not zero cylinders at idle? Not that I'd want that, the less deactivation the better as far as I'm concerned. MPGs are toward the bottom of my priority list. I'm especially thankful for not having the stop/start feature of other makes trying to milk an mpg or fraction thereof.
 
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True or false, all 4 cylinders are pumping at all times, the shutdown being the fuel injection?
 
True or false, all 4 cylinders are pumping at all times, the shutdown being the fuel injection?

False.

Injectors stop and valves close, so those cylinders function as air springs. The spark plugs continue to fire to reduce heat loss.
 
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