Cylinder Deactivation

[XR250]

Maybe TLDR.
I have a 2023 Mazda3 6MT with a 4 cylinder 2.5 engine. It has cylinder deactivation where it runs on two cylinders under certain operating conditions. It does this by energizing an oil control solenoid which pushes a pin out of the hydraulic lash adjusters causing them to collapse instead of the rocker arms pushing down the valves.
On the highway, it is pretty unobtrusive and provides pretty impressive fuel economy. Around town though, it is annoying AF. Anything under 2k rpm, it vibrates when in CDA mode. As such, I always find myself driving one or two gears lower than I normally would to keep the RPMs above 2,200 where it smooths out nicely. I typically would like to drive at 1,500 RPM's as the engine has no problem doing this and the "suggested gear indicator" always wants me there for best fuel economy.

None of the aftermarket tuners are able to access this part of the ECU to turn it off. As such, I took matters into my own hands by simply disconnecting the CDA solenoid electrical connector. Sure, I have a constant check engine light, but the car seems to just use the non-CDA map. It is like a completely different car now. So much more enjoyable to drive. I am actually getting better fuel economy as I can drive in higher gears around town without the annoying vibration of 2 cylinder mode.

So other than CEL, i see no downsides to this. I suppose if there is an unrelated fault, I will not know as the CEL is already on. However, I feel like that would be pretty apparent in the driveability.

Y'all have anything for me?

 

[Lou Scannon]

Sounds pragmatic to me. You might as a precaution check codes with a scanner periodically just to make sure nothing is being missed.
rant/ My late model Grand Marquis defaults to use overdrive at speeds above 35 or so, which is way too low for overdrive, so it is always downshifting or coming out of lockup for the slightest hill or accell. So, every trip, I have to manually disable overdrive, and manually engage it only when I want it, e.g. for steady cruising above 45. /rant

 

[gruntguru]

Sounds like you need a deactivate switch on the dash so you can activate the system during highway driving. If you use a changeover switch you could include a resistor to fool the ECU that the solenoid is still connected.

 

[XR250]

@lou - That would annoy the crap out of me. Good idea to check the codes

@gg - Maybe i'l try that after the warranty expires.

T

 

[System Protection]

Does it have a Sport Mode? That will deactivate it on some cars.

Also look into FORSCAN. I think it works on Mazda too.

 

[3DDave]

A brief look at Mazda forums show some have the same issue; no solutions.

 

[XR250]

Yup, been thru all of that.

 

[MintJulep]

include a resistor to fool the ECU that the solenoid is still connected

I don't think that's a good idea.

@XR250 reports that with the CDA valve disconnected the ECU seems to fallback to 4-cylinder mapping.

Running on 4 cylinders with 2 cylinder mapping, as would probably happen if you spoof the input, is probably bad.

 

[XR250]

Agreed MJ

Does it have a Sport Mode? That will deactivate it on some cars.

Also look into FORSCAN. I think it works on Mazda too.

Only the slushboxes have sport mode. Forscan will not address this as far as I can tell. One of the tuners asked me to pull codes while the CEL is on. He said he may be able to use that to tune it out. I'll let y'all know if that pans out.

 

[TugboatEng]

Can you install two of the regular lifters in the deactivation bores and just let the system think it's doing its thing?

It's not good to lug engines. Subaru drivers are fascinated with lugging their engines and they break piston ring lands because of it. A little piston speed is important. There is talk of bringing back opposed piston engines for this reason (Achates).

 

[XR250]

Can you install two of the regular lifters in the deactivation bores and just let the system think it's doing its thing?

It's not good to lug engines. Subaru drivers are fascinated with lugging their engines and they break piston ring lands because of it. A little piston speed is important. There is talk of bringing back opposed piston engines for this reason (Achates).

That would not work as it cuts the fuel in those cylinders and uses a completely different map. It also has a valve in the exhaust system that activates under 2 cylinder mode.
The engine is perfectly smooth and happy at 1,500 rpm. The shift indicator wants me to have it down around 1,300 sometimes. I typically will not go below 1,500 though.