'Flat-spot' - Mazda CX-30

[mph999]

Hey Guys,

Thought I'd pick your brains before I head to the dealer.

I have a CX-30 (Auto, Registered March 2020) with the Skyactive-X engine. I've owned it since Feb this year, it had 21000 miles, now about 24500.

This past week it's developed what I can best describe as a flat spot, it tends to happen just as it changes gear at around 2300 rpm, initially it felt like it was changing gear twice - however, if you stick it in 'manual' you still get it (without the gear change) - so I don't think it is gearbox related.

I've felt in in 2nd, 3rd, 4th - I'd say mostly 3rd but that's the gear most suited for the roads I've been testing on. One thing I've just realised is I didn't try in under hard acceleration, but certainly in normal driving, you'll get a brief loss of power (I presume) felt as a slight 'jolt' at around 2200 to 2400rpm.
It's intermittent - at least these past couple of days you'll feel it a couple of times within 10 mins - that said, I didn't notice it at all on Friday, well, maybe once but very slight.

Seems other have reported it:

https://www.cx30talk.com/threads/skyactive-x-flat-...
https://www.mazda3revolution.com/threads/e-skyacti...

I'm not accepting it as a characteristic as suggested in some of those posts because it wasn't doing it prior to this past week.
It's not the fuel as this would happen all over the place (+ I've filled up since it started)
It's not when switching to SPCCI, because at those speeds / throttle position it's always in SPCCI (spark controlled compressive ignition - it's really only not in SPCCI when idling or very low rpm)

Any ideas ?

KR

mph999

[350Matt]

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out causing rough running.
As its a mechanical fault it may not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.


best method to find a leak is to use a smoke machine,

or you can have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.

[mph999]

350Matt said:

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out causing rough running.
As its a mechanical fault it may not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.


best method to find a leak is to use a smoke machine,

or you can have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.

Thanks Matt - yep, I was thinking originally if it could be the mass airflow sensor, but with no code I figured not, but your suggestion is in the same kinda area.

I'll have a look tomorrow, failing that it can go to Mazda (it's under warranty + my local dealer is actually pretty good) - suspect they'll also have a smoke machine.

Cheers again,

Martin