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Get the service manual, pull the intake manifold and look at the intake valves for yourself...and take photos if there is carbon buildup. Mazda says that valve overlap prevents this, but I'm not sold given other people saying they have benefited from sea foam cleaner.

Also do direct injectors ever need to be cleaned? I know somebody else here said their car benefitted from some injection cleaner.

Also are you running a slippery oil like the factory oil? Not all 0-20s are created equal.

Freakish of all, you could check the engine compression to make sure there isn't an issue with combustion chamber sealing.
 

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RT03, I only use regular 87 octane gas, not premium. Filled gas today, previous tank gave exactly 30mpg with 65% city driving , lot of lights and stop signs. I also thought Tecron would do nothing for DI engine , added it as I figured it would'nt harm either but was pleasantly surprised by the engine smoothness and responsiveness. I would be more curious to see how Techron does in severe winter months of Jan/Feb because last year my mpg dropped to 27 those months and I did not use Techron.
Does the smoothness and responsiveness stay with the next tank of gas without the Techron?

The Techron is an additive that may be having the effect of raising the octane level of the tank of gas, which would cause the engine to run smoother and more responsive than 87 as noted on the octane thread.
 

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This is my third tank after Techron , the smoothness and responsiveness is still there. I intend to put Techron once more in January to cover the winter.
Thanks for responding. I wanted to rule that out. I'll be using some techron as well once I hit 5k.
 

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Glad to see you are seeing the benefit racing tiger, but I'm with tickerguy that I think this huge change is pretty much just attributed to the injectors.

Not to say there couldn't ultimately be some carbon buildup on the intake valves as well, since 2014mazda6 member said running the seafoam treatment improved his engine smoothness and had a small impact on fuel economy.

I would be curious if somebody with high miles on their mazda 6 that hasn't run any cleaners could do a borescope inspection of the tops of the intake valves to see if they are shiny clean or something else...

I'll definitely be running some techron through my engine before too long here as a routine maintenance.
 

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Does the 6 have a real fuel filter? My Miata didn't.


It may have been something freakish, or it may be something isn't quite right with one or more of your injectors. If it starts to crap up over the next 10-20k you may need to replace the injectors.


I'd at least notify the service department of your local mazda dealers to put it in your records that you had injector clogging issues.
 

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Racing Tiger, If I was in your shoes I would, despite your other cars never having problem with Pilot and BP gas, still make a new habit of filling up at a different subset of gas stations for the Mazda 6. If the problem happens again you will be able to completely rule out the brand/type of gas causing the problem.

Also, you should try "racing" your wife in the miata while on 93 octane again, perhaps you would be able to keep up now that your injectors are clean?
 

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Hey guys, I too have horrible mileage. My car is at 25k miles. First 10k miles I'd average like 29 mpg. Now it's down to 23 and only going lower. I dropped it off at the dealer yesterday for a rough idle and bad mileage, hoping to get the injectors, MAF etc looked at. Will report back once I get the car.
See if they can peek at the tops of the intake valves too! Everybody is wondering how this DI engine does for intake valve deposits...mazda says the intake valve timing keep it clean, but...
 

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Hey everyone, got the car back today.

They fixed my door insulation (thank God, the car was WAY too loud), but no luck on finding the cause of my bad MPGs. They checked MAF, filters, injectors, etc. They even said injector cleaning at 30k is part of their maintenance plan.

On the upside, Andy is the Master tech at Tustin Mazda, and he is the most awesome tech from a dealer I have ever talked too. Per my personal request, he took the car in the back and gave me all the diagnostic print outs to see if anything came up. Nothing did, but still nice of him to do so.

Other than that, I guess I will be going the fuel additive route to see if that helps as it did in your case.

Other than that, the only thing I can report is that I am due for tires and I am going with Michelin Pilot Super Sports. I will do some canyon carving and report back. Soon, I am planning on adding a swaybar and upgrading to EBC pads and rotors, and also adding in a drop in filter. Nothing major to the car after that. MAYBE some auto.exe stuff, but without Torsional-Stiffness here to answer my questions I am holding off!


Did they check the intake Valves? Oh, well, someday somebody will.


BTW I noticed my mileage dropping too, so I dumped the techron in the current tank. I also checked my tires for the first time since the warm fall and they were down to 25psi...ok that explains it. So I got them back up to 35ish, and I expect mileage to substantially improve. With the colder weather it definitely drops the tire pressure. Interesting the TPMS never said boo. That explains the recall, but man I don't want any warnings flashing at me all the time like it has been for some people.
 

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200,000 miles at 12k per year is around 16 years off the top of my head, I don't think that is unreasonable to spend an extra 1,333 dollars in todays dollars over 16 years for the extra enjoyment and satisfaction and cleaner running engine of the higher octane and possibly even better gas mileage. And most everywhere I've been in my life it's an extra 10 cents for every 2 octane.


I really think 93 is a bridge to far for this car stock or even modified, but without a tune. I DO get better MPG on 91 vs 87, but I'm not so sure I would still be even better at 93, it could be worse.
 

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My throttle is also more responsive now to slight pedal push (never used Moly nor ever filled anything but 87 gas), so I attribute this to wear on the pedal linkages making them smoother and easier to glide (kind of a break in).
The gas pedal is electric. Its just a resistor and a spring. There is more power with less throttle because the timing is being further advanced and burning the same amount of gas and air more efficiently. So it isn't your imagination or the pedal depressing easier.
 

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RacingTiger, are you sure the stock tires weren't LRR to begin with? You say the new LRR tire has significantly better handling than stock which makes me skeptical it has lower rolling resistance of any significance. And nitrogen won't change RR.

You probably are at the point where you need to have the intake valves checked, or at the very least run the seafoam experiment yourself.
http://forum.mazda6club.com/engine-drivetrain/289505-seafoam-cleaning-our-2-5-skyactive.html
 

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This article I read said that no one gas brand's detergent mixture is perfect. Based on these imperfect detergent additives each will keep certain areas of the injection system and combustion chambers clean AND LEAVE DEPOSITS on other parts of the system. I think it has to due with the different detergent formulation's performance at certain temperatures as different parts of the combustion chambers and intake system will experience and maintain slightly different temperatures. That seemed pretty reasonable to me. The article went on to say that if you continually switch brands, even top tier brands, the different formulations will not only create deposits in different spots but also REMOVE deposits in areas that the other brand created. The whole point of the article was to recommend that you stick with "the devil you know". Pick one top tier brand and stick with it and, even better, stick with one gas station if you can.
This is borderline hilarious. The first part sounds reasonable, but why would you reach that conclusion? It's like saying all kinds of food are different so you might as well just eat one kind of food the rest of your life.

I reach the exact opposite conclusion. If you routinely change from one gas station to the next of top tier, you are unlikely to get significant buildup in any one area and each one works on a different area with detergents keeping all areas of the engine relatively clean.
 

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My last post in this thread, I give up. 35MPG would look good about now. Filled up with 87 this time around to see if maybe just MAYBE 93 was keeping me out of the 36+ zone. Nope.. it was a crutch. 28MPG 100 miles into this tank all HWY, 0 idle time, could NOT get above 36 even on the instant trying like hell. (70MPH MAX) 37,980 miles... #$!#$%@#$^%@$^[email protected]#%$^$%&^$&$%!#[email protected]#[email protected]#[email protected]!$. /rant /thread.
Your mileage continues to deteriorate. Clearly your engine has a problem.

If it isn't buildup on the intake valves, likely another component is slowly deteriorating in its function. You don't have a check engine light on, so it may not be the MAF sensor, o2 sensor or spark plugs, but then again, it may not be bad enough to trigger a fault, but could still be affecting mileage. I would look at the injectors and and probably last, consider checking the coils. other wild potential problems are a clogged air filter, or some other restriction in the exhaust? Even the throttle body should be questioned. It's a bit of a wild goose chase until the problem gets really really bad, unless you can get some diagnostic guy that can check each of the items for proper function.

On my Volvo my MAF was bad for a while giving me bad gas mileage, but it wasn't until a re-oiled airfilter really trashed it that the check engine light came on. When the maf was replaced the car finally got good gas mileage for the first time since I had bought it.
 

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In case it is just carbon on the intake valves causing mileage to drop, I'm almost completely turning off the EGR valve with my Orange Virus Tune.

I also requested from JBR when they were going to come up with an EGR block off kit for the skyactivs.

Those with the dropping mpg issue should try the CRC Intake Cleaner mentioned above to see if it makes any difference.
 

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Keep in mind that if you block off the EGR, your combustion temperatures and tendency to knock will increase. I think you already run 93 octane, but if not you will certainly need higher octane fuel after blocking the EGR. I found this out when tuning a GM 3.8L back in the day :)
Your assessment is mostly valid for an EGR block off plate, although I don't know how adaptable the stock ecu settings are to adjust valve and spark timing for that.

However for our car with a proper modified ecu tune, an EGR valve is a piss poor way of managing compression ratio and knock when you've got an ultra-expensive electrically phased intake cam timing system that can do the same thing (limit the air mass in the intake stroke) without introducing hot exhaust air full of uncombusted crap back into the combustion chamber. It should have even less knock and take advantage of even more timing advance with the EGR valve closed because of that.

So with a tune my mileage will improve with no increase in knock on the same octane after almost completely disabling the EGR valve.
 
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