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Discussion Starter #22
Did they find the root cause of the issue?
Nothing yet. The Technicians seemed to be talking a lot about build up due to the direct injection fuel delivery system but no official next steps yet. I suspect that's why they scoped the engine last time I was there.
 

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I think you do NOT want to consider a non-turbo Mazda these days. They have Cylinder Deactivation... wherein they go from 4 cyl. operation to 2 cyl. operation. Experiencing BIG prbs in 2019 & 2020 Mazda3's... evident at www.mazda3revolution.com. I personally would not consider a Mazda3 after 2018 model year... and indeed I would not consider a nonturbo Mazda6 for 2018 onwards. I hav not actually heard of Mazda6 prbs with this system though. I am fundamentally opposed to the concept, however. It offends my "mechanical harmony" sense as a mechanical engineer.
I want to correct my comment about not having heard that the normally aspirated 2.5 in the 6 was experiencing vibration problems with the Cylinder Deactivation system... Witness post no. 57 (on p. 3 of this Mazda3Revolution thread) where the individual talks about his '18 Mazda 6 2.5:

Cylinder deactivation issues.

Be glad many of you have 2.5 T's... with no CD system...
 

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Discussion Starter #24
I want to correct my comment about not having heard that the normally aspirated 2.5 in the 6 was experiencing vibration problems with the Cylinder Deactivation system... Witness post no. 57 (on p. 3 of this Mazda3Revolution thread) where the individual talks about his '18 Mazda 6 2.5:

Cylinder deactivation issues.

Be glad many of you have 2.5 T's... with no CD system...
Geez, thanks for sharing that. I didn't realize that this issue was pushing some driver's to consider selling their brand new 3s. Really unfortunate. I thought this was all solved with that update. Eep!
 

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If the spark plugs and coil packs were replace but didn’t resolve the issue then work your way to the airflow sensor. Process of elimination. My guess is still a faulty afs.
Check for air leaks between the sensor and engine. I know it sounds basic and simple, but I forgot to do it after some time and money.
 

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Howdy, Just thought I'd share the latest with my 6.

Current mileage is 105,000kms.

Condition has degraded drastically. Car is now sputtering bad when stopped in drive, feels like it's going to stall. Idling low at 500-600 rpm. I have a check engine light now and it's throwing Misfire in cylinder#2 code. Has been to dealer 3 times for diagnosis for this issue and another (OCV leak). You can feel one cylinder is misfiring as there is a methodical thump in the whole car when it's idling. Seems ok when driving at speed, though. They ran a scope into the engine today to check for carbon build up due to direct injection, my guess is that's the latest fix they are going to try (carbon cleaning). So far I've been told car needed a new injector, needed new spark plug as the current one was cracked, and also told engine may need to be completely replaced. Currently awaiting next step instructions from Mazda Canada.
Howdy, Just thought I'd share the latest with my 6.

Current mileage is 105,000kms.

Condition has degraded drastically. Car is now sputtering bad when stopped in drive, feels like it's going to stall. Idling low at 500-600 rpm. I have a check engine light now and it's throwing Misfire in cylinder#2 code. Has been to dealer 3 times for diagnosis for this issue and another (OCV leak). You can feel one cylinder is misfiring as there is a methodical thump in the whole car when it's idling. Seems ok when driving at speed, though. They ran a scope into the engine today to check for carbon build up due to direct injection, my guess is that's the latest fix they are going to try (carbon cleaning). So far I've been told car needed a new injector, needed new spark plug as the current one was cracked, and also told engine may need to be completely replaced. Currently awaiting next step instructions from Mazda Canada.
105K is a lot of miles for a 2 model year old car, how was it maintained including oil changes? One spark plug was reported to be cracked, what is the real story on that because plugs don't crack by them selves. The plugs for this car were scheduled to be replaced at 75K, were they? Was one cracked a while back during the plug change and malfunctioned up recently? I broke a few spark plugs myself many years ago installing or removing hard to get at plugs on a V8 engine but these plugs are not difficult to replace.
After replacing the cracked #2 plug and miss fire is still present and trouble shooting a problem at home, it don't cost anything to swap coils to see if the miss-fire changes cylinders. If so, replace the #2 coil in this case and done. If not a coil, time to dig deeper, the #2 injector would be next to check into and replace if necessary. If this engine ever overheated it would be wise to do a compression check to check the health of this engine.
At 105K miles carbon build up on intake valves shouldn't be a big issue yet with a non turbo engine. Turbos force far more crankcase oil fumes into the intake system causing the carbon issue. Many people are are installing oil catch cans on their direct injection turbo engines to eliminate this carbon build up.
 

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Discussion Starter #29
105K is a lot of miles for a 2 model year old car, how was it maintained including oil changes? One spark plug was reported to be cracked, what is the real story on that because plugs don't crack by them selves....
That would be 105,000 kilometres, not miles. Still high but not as high if it were in miles.
The Signature has a turbo engine so the maintenance schedule is different than the one for the NA 2.5 that you are citing.
Maintenance schedule has been meticulously followed as per Mazda's requirements, including spark plug replacement.
Some good trouble shooting suggestions. Thank you for that.
 

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Discussion Starter #31 (Edited)
Any update on the issue?
Nothing yet so I requested a rental and dropped the car off yesterday. I have no idea why Mazda Canada is dragging their heels on providing solutions to the Tech's but I am happy my dealer agrees that it's past reasonable.

I grabbed some videos of how rough the engine was running. Just posted them on YouTube. The car is shaking itself to sh!t when in drive with foot on the brake. I am surprised of how much of that vibration the engine mounts are absorbing...very impressive.

The Dodge Charger I have is pretty smooth but wow...makes me really appreciate the elegance and richness of the Mazda 6!


 

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Discussion Starter #32 (Edited)
Here's another video. Interior is wobbling because of the misfire. The whole car bounces. Yes, I know the video is shot the wrong way but how else was I going to get the whole pop bottle in the shot ;)
The interior lights are actually dimming along with the wobble as the car is idling so low it isn't generating enough juice to keep them steadily lit.

 

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Discussion Starter #33
Just as an aside, this Charger I have rented...it's interesting. Really not a driver's car, seat is so stiff and uncomfortable. I feel like I am on the car and not in it and it feels HUGE on the road plus the drivetrain is clunky but the engine is very smooth and sounds alright. You can tell it's heavy as heck. Loves to rev out.

But check out this fuel economy on my drive home! This was driving around 100 km/hr on my commute home for about 120 kms. Weather has been cruddy here the last few days so speeds are slower than usual on the highway.

6.3L/100 kms!! I think that's around 37 MPG? That is mega impressive for a RWD, just-shy-of-300 hp V6 large car! I guess this is where you see the benefit of the 8 speed transmission...revs are so low on the highway (1500 or so RPM). I do like how my Mazda6 is always in the right gear and has so much torque it doesn't need to shift nearly as much as this beast does but I think the Dodge does a pretty good job of handling all the gears.

Also, the RWD is really fun to play with in the snow and ice.

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I think the Pentastar 3.6 is a decent engine. 9 speed A/T is I believe a jt. venture with ZF. Transmission has "range select" control ... not "manumatic" control. 'Gotta say I prefer the former. There are subtle differences between the two... and folks soon tire with the latter.
 

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Discussion Starter #35
I think the Pentastar 3.6 is a decent engine. 9 speed A/T is I believe a jt. venture with ZF. Transmission has "range select" control ... not "manumatic" control.
Yeah, this one has the 8 speed which seems to shift less than the 9 speed, I guess that is sort of obvious but I hope you get what I mean.
 

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Dang that's a crazy misfire under the hood. Definitely wouldn't be trying to drive that.

Your interior bouncing vid kinda looked like that thing that's happened to mine a couple of times in the way the momentum was shifting in the car - but I don't think I was having a misfire at the time. Next time I get that bounce happening I'll try putting it in park, getting out and listening for similar sounds.

*knock on wood" I haven't has the bouncing issue since my last post on the subject.
 

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Discussion Starter #38
Dang that's a crazy misfire under the hood. Definitely wouldn't be trying to drive that.

Your interior bouncing vid kinda looked like that thing that's happened to mine a couple of times in the way the momentum was shifting in the car - but I don't think I was having a misfire at the time. Next time I get that bounce happening I'll try putting it in park, getting out and listening for similar sounds.

*knock on wood" I haven't has the bouncing issue since my last post on the subject.
It's interesting you say that because you can really only see how bad the balance is off when when the car is idling really low.
The only way I could get it to do this and capture it on camera was to have the brake applied while in gear. When in this state, the idle goes below 500 rpm and it runs really rough.
For example, when coming to a stop in traffic, idle goes down to 800 or so for a few seconds than it goes much lower to 500 when sitting and idling and this is where things seem to go off the rails. Having said that, as soon as I took the Service Manager out for a drive he said he could tell it wasn't running right by the sound of it as soon as I started pulling out of the parking spot but the Check engine light was off at this time.

If you have access to a scan tool and can find the time, I would highly recommend checking for stored codes. My car had this misfire code stored but it never happened again in a close enough time frame to illuminate the check engine light. It was actually when I was looking around to diagnose an oil leak that I happened to find out it had the stored code and after that the CEL came on.

I suspect the car had this code stored for a very long time and the occurrence was far enough apart in time that it never trigger the CEL.
 

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Discussion Starter #40
Speaking from experience you should definitely have the dealership look closely and replace the air flow sensor. My car suffered from the same symptoms as yours poor idle 500-600, cylinder misfires, and would randomly stall at stop lights. Make sure they use oem mazda parts and not some off brand. Best of luck to you. Thank me later.
So they are checking this part ( mass air flow sensor) now. The decarb did not fix the issues.
 
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