[Jhannah469]

If it were up to me, (its not), I would not add the complexity of cylinder deactivation to gain one mile per gallon. Not worth it. But, I have it now, and I 'll have to live with it. It already failed once, and caused this brand spanking new 3 to spend a month in the shop waiting for parts from Japan. Its fixed now, and so far the car is running great. We'll see.

What happed when it failed? Did it stop running completely and we’re you driving when it happened?


Sent from my iPhone using Tapatalk

 

[rpg51]

The car went into limp mode intermittently. Yes, while driving. I could get where I was going, at about 25% power or so. The dealer explained it by telling me that there is a part incorporated in a section of the exhaust that varies the back pressure provided by the exhaust depending on whether the engine is running on 2, or 4, cylinders. That part was not working properly. The system sensed the wrong back-pressure and put the engine in limp mode to protect it from damage.

 

[Jhannah469]

The car went into limp mode intermittently. Yes, while driving. I could get where I was going, at about 25% power or so. The dealer explained it by telling me that there is a part incorporated in a section of the exhaust that varies the back pressure provided by the exhaust depending on whether the engine is running on 2, or 4, cylinders. That part was not working properly. The system sensed the wrong back-pressure and put the engine in limp mode to protect it from damage.

At least it wasn’t an internal valve mechanism that could have damaged the engine.


Sent from my iPhone using Tapatalk

 

[da2el]

I still have not understand. Is some people getting a physical part replaced in the exhaust? Others just a software update? Are we talking about the same recall or 2 different ones?

 

[Jhannah469]

I still have not understand. Is some people getting a physical part replaced in the exhaust? Others just a software update? Are we talking about the same recall or 2 different ones?

The software update is the recall. The exhaust valve part is not. At least I have not seen a recall for the exhaust valve.


Sent from my iPhone using Tapatalk

 

[2.0_Mazda]

If it were up to me, (its not), I would not add the complexity of cylinder deactivation to gain one mile per gallon. Not worth it. But, I have it now, and I 'll have to live with it. It already failed once, and caused this brand spanking new 3 to spend a month in the shop waiting for parts from Japan. Its fixed now, and so far the car is running great. We'll see.

I'm curious, how did it fail?

The recall was already applied to my car when purchased but I'm a little worried about long term reliability. I do see instant fuel economy improvements when the cylinder deactivation engages but there is a noticeable droning sound when engaged.

 

[rpg51]

As far as I know, the problem I had (required replacement of an exhaust part that varies back pressure) is not the subject of a recall. I have not heard of anyone else with this same problem.

EDIT: Someone above referenced exhaust VALVE. My problem had nothing to do with exhaust VALVES.

 

[arathol]

As far as I know, the problem I had (required replacement of an exhaust part that varies back pressure) is not the subject of a recall. I have not heard of anyone else with this same problem.

There is nothing in the exhaust system that regulates back pressure. :dunno:
I think what you are referring to is a shutter that blocks off the part of the exhaust that isn't used when the cylinders are de-activated. This keeps the exhaust flow normal and prevents reversion pulses from traveling up and down those unused pipes, something that can cause a bunch of problems for the cylinders that are still running. If that shutter is not opening when it should the engine won't run right if at all....

 

[iwolffy]

The transmission for 2019 is a bit different from previous years. Most likely the extra fluid has something to do with the vibration dampening mechanism... Or not.....:dunno:

Yes, this is it.

"Because the firing interval is doubled when running on two cylinders, the engine is more likely to cause vibration than when using all four cylinders. A centrifugal pendulum damper adopted in the torque converter for the six-speed SKYACTIV-DRIVE automatic transmission compensates for this. By generating counterforce that responds to fluctuations in engine torque, the centrifugal pendulum damper suppresses the transmission of unpleasant vibrations into the cabin. "

 

[rpg51]

There is nothing in the exhaust system that regulates back pressure. :dunno:
I think what you are referring to is a shutter that blocks off the part of the exhaust that isn't used when the cylinders are de-activated. This keeps the exhaust flow normal and prevents reversion pulses from traveling up and down those unused pipes, something that can cause a bunch of problems for the cylinders that are still running. If that shutter is not opening when it should the engine won't run right if at all....

Interesting. The service guy told me it affected back pressure. Guess he didn't know what he was talking about. But yes, the word shutter was used.

What part of the exhaust isn't used when running on two cylinders? I'm trying to visualize how that works.

Came across this: diagram - https://corksport.com/blog/wp-content/uploads/2019/04/mazda-6-exhaust-header-diagram.webp. might be the 2019 3?

 

[arathol]

When the cylinders are shut off only two of the four primary exhaust pipes (#1 through 4 in the CS diagram) are used because there is no ignition in those cylinders. (cylinder 1 and cylinder 4 get shut off)
Because there is no ignition there is no exhaust pulse traveling through those two pipes. Those unused pipes create what is virtually an empty chamber, and exhaust pulses from the active cylinders will travel up them then echo back into the exhaust stream, causing a reversion-type obstruction to the flow from the active cylinders. If those two pipes are closed off at the collector where the flow from all four pipes enter the exhaust system, the flow from the two active cylinders will be normal. I assume that the shutter assembly the tech referred to would be placed somewhere between the primary collector and secondary collector where the flow from cylinder 1 and 4 enter the main exhaust stream. Since exhaust gas velocity is critical to the operation of the SkyActiv engine, anything that restricts the flow will reduce gas extraction from the cylinder, causing cylinder temperatures to go up and leaving residual unspent fuel in the chamber. This causes knock or pinging, which, when detected by the knock sensors, causes the ECU to pull engine timing until the knock is gone.

 

[rpg51]

Interesting. Isn't the exhaust stroke just pushing "clean" air instead of burnt exhaust gases at exactly the same velocity that it does when there is normal ignition?

Seems like back pressure is part of what you are describing, no?

I gotta say, it all seems terribly complex for a very small gain in fuel economy. Lots of stuff to break.

 

[sandy]

can't wait for the X>

 

[arathol]

Interesting. Isn't the exhaust stroke just pushing "clean" air instead of burnt exhaust gases at exactly the same velocity that it does when there is normal ignition?

Seems like back pressure is part of what you are describing, no?

I gotta say, it all seems terribly complex for a very small gain in fuel economy. Lots of stuff to break.

No, if you watch the video demonstration you can see that the valves don't open when the cylinder is de-activated, so there is nothing being pushed out and the two primary pipes are just dead space.
As for the back pressure, sort of but not not really. The exhaust system is designed to provide maximum scavenging. Basically the timing between pulses exiting the exhaust creates a vacuum that draws the hot gasses out. The empty pipes can create a reversion wave that will disrupt the scavenging and make the exhaust less efficient.
Yes, it does seem like a lot of work went into making a simple thing into a Rube Goldberg device. Lots to go unnecessarily wrong for very little return.