CX-9 Engine problems, constant P0306 codes - Please help!

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2009 Mazda CX-9 Sport AWD
First time here in this forum; I hope somebody can help. I have a 2009 CX-9 Sport AWD w/50k miles (very low miles). 2 months ago, wife noticed engine running very rough and check engine light came on (solid). Checked with my scanner and found (2x) P0306 [cylinder 6 misfire]. After Google search, found many saying plugs need to be changed between 50-60k. No problem changing front 3, but the rear 3!?!? Had to go in for inspection anyway, so paid mazda to do it & troubleshoot the code. They said the coil pak on cyl 6 had "internal fault" and replaced, along with all plugs and new PCV valve.
1 week later, rough startup, check engine light, and heavy white smoke coming from both exhaust pipes (outdoor temp 80-90F - this was not startup condensation!). Took back to Mazda dealer. Found P0306, P0316, P0206 codes. Replaced cyl 6 injector.
3 weeks later, noticed the engine running VERY HOT with A/C on, almost overheated. Engine running rough again, check engine light on, P0306, AGAIN!!! Removed oil cap and found white "gunk". Took back to dealer. Removed (new) spark plug from cyl 6, found "carbon deposits". Swapped plugs with cyl 4 and got misfire code on cyl 4; determined bad spark plug. Replaced with new spark plug. Performed compression test on all cylinders, ~ 175psi each. Added 1/2 gallon of FL-22 coolant and performed pressure test; no leaks. Mechanic said the white gunk was just condensation. Where did 1/2 gallon of coolant go and why did I experience 2 episodes of heavy white smoke??? No answers
A few days later, engine running rough on startup, check engine blinking, then solid. When I say running rough, I mean bucking, shaking. Back to the dealer. More P0306 codes. They called Mazda, who said to replace the PCM. Currently waiting for the part to arrive.
Has anyone ever heard of anything like this?? This vehicle is driven primarily on very short trips (2.5 miles each way to work + normal weekend driving).
I've asked multiple times if they've checked the crankshaft position sensor and pulley, but they insist there would be a code if there was a problem. Also still no answer as to where 1/2 gallon of coolant went. I asked them to change the oil again and inspect for any signs of coolant (less than 500 miles since last change).
What am I missing here??? The thing they haven't checked is the intake manifold gasket. In my experience, lost coolant & white gunk = one of 3 things:
1. Intake manifold gasket
2. Head gasket or cracked head
3. Cracked engine block

HELP, PLEASE!!!!!!
 
I'm with you on the head gasket. Anytime I've seen "white gunk" under the oil cap and you're low on coolant leads me to that conclusion. Could be something else, but...
 
You really need to stop going to that dealer and find a real shop capable of troubleshooting an issue instead of just throwing parts at it.

White smoke, overheating, running rough and coolant missing? Sounds like an expensive shot in the dark to be replacing a PCM at this point. Has the dealer agreed to eat the cost of the PCM if doesn't fix it? Your problem is indicative of a real issue with dealership service departments. They've become far to reliant OBDII codes telling them what area to throw parts at and extended warranties allowing them to get away with that lax troubleshooting because the vehicle owner doesn't pay.

Really sounds like a head gasket to me.
 
The PCM is being covered under the 7yr/100k powertrain warranty. I think they're wasting their time & money. Unfortunately, I think I have to stay with the mazda dealer for the warranty work. I think they should be spending their time searching for the leak. Waiting to hear back on the oil change inspection. There should be signs of coolant in the oil if it is a major engine failure. And if so, I would expect them to switch gears...
 
In sure you're already doing this, but make sure to save all the receipts and document everything: repairs, conversations, etc.
 
The PCM is being covered under the 7yr/100k powertrain warranty. I think they're wasting their time & money. Unfortunately, I think I have to stay with the mazda dealer for the warranty work. I think they should be spending their time searching for the leak. Waiting to hear back on the oil change inspection. There should be signs of coolant in the oil if it is a major engine failure. And if so, I would expect them to switch gears...

If they're doing it under warranty I'd say let them replace away. The minute they start continuing their parts guessing game with parts you're expected to pay for I'd bail for a reputable independent shop that still understands how to troubleshoot an issue.
 
So... Just as I thought, the PCM replacement did nothing. Finally, Mazda tech support recommended to the tech to check for leaks around the head gasket. Guess what??? Surprise Surprise! Both head gaskets leaking. They replaced the gaskets, flushed the engine, and then gave to their driver for road testing. Can anyone guess what happened next???

That's right, he wrecked it!!! I've never owned such a jinxed vehicle. I was/am out of town while all this happened. Going home next week to deal with this problem. If the dealership is smart, they will replace the vehicle. There's no way I'm taking this one back! Hope it doesn't have to involve lawyers. This one is pretty straight forward. You wrecked my vehicle, you now owe me a like vehicle.

Anyone else ever go through this??? Would love to hear about the outcomes of others.
 
Wow! Hopefully it's totaled and you don't even have to worry about lawyers.
You've got to post pics! Glad you weren't driving and hopefully this will be the last of any bad luck with this vehicle.
 
Anyone else ever go through this??? Would love to hear about the outcomes of others.

Not personally but I know a guy who did. The car wasn't totaled, not even close, so the dealership just sent it over to their body shop and fixed it up good as new. They gave him some free oil change coupons for his trouble.

As far as getting a lawyer involved because you want a replacement car, good luck if it's not totaled or at least close to the threshold for being totaled. It's no different than someone hitting you in traffic and them being 100% at fault. They (or more specifically their insurance company) are responsible to put your vehicle back to pre-accident condition, not simply replace it. You can fight about things like diminished value because it went from a clean carfax to 1 accident car fax and may get some extra money out of it but there's no legal responsibility to replace a vehicle that can be repaired.

That said, it might be a good time to use the goodwill they're likely to extend you to make this all go away to trade up on a newer CX-9. How much goodwill you get will likely depend on the circumstances of the accident. IE, was their driver at fault.
 
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