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My Mazda6 has racked up 75,000 miles already, so in the past three months I have experienced power loss and the fuel economy is going down in the gutter. I'm getting like 20 mpg on highway and 15 mpg on city. I don't have any CEL. When, I push the gas pedal, there's a lot of hesitation in terms of acceleration, like pulling a boat or something, and sometimes it would buck back and forth. I did the maintenance such as changing the spark plugs at 75k miles (OEM plugs), changing the oil at 5k (Castrol EDGE Full Synthetic) with OEM oil filter (also I put the fuel cleaner [Chevron Techron] after each oil change, changed the air filter (OEM) at 75k miles, and cabin air filter too.

So, what is the issue? Is it in need of "fuel induction service" that the stealership keeps pushing me to buy? Or is the intake valve full of carbon deposits?
 

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Have you cleaned the throttle body and MAF?
 

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No, I have not cleaned both of things.. I don't know how to do it though
Would make it easier to help if we knew the year.

Here are some vids from youtube. Hopefully your year/gen is there.

 

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It is extremely unlikely that TBI cleaning and such will do anything.

Check your brakes -- carefully. Drive for a while then get out and feel (CAREFULLY!) the hub area; if you find a hot one (or more) you have a dragging caliper, which will do severe damage to your fuel economy.

It's likely also spark plug time, and also check your air filter.

That's where I'd start.
 

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Discussion Starter #7
It is extremely unlikely that TBI cleaning and such will do anything.

Check your brakes -- carefully. Drive for a while then get out and feel (CAREFULLY!) the hub area; if you find a hot one (or more) you have a dragging caliper, which will do severe damage to your fuel economy.

It's likely also spark plug time, and also check your air filter.

That's where I'd start.
Thank you tickerguy for your advice. The spark plugs has already been replaced, and air filter too.. I have been noticing the steering wheel has been shaking slightly while braking at the highway speeds (65+ mph), meaning I might have warped rotors.
 

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Im at 79,000 miles on my 2015 Mazda 6 GT with i-eloop and i get about 30mpg thats with non spirited driving and majority highway miles. I use to get at least 35mpg but to be honest it was never the same once i changed to a short ram k&n intake and the racing beat axle back exhaust. I’ll be putting the stock intake back on the car to see if it helps gain back some mpg. I’ve also never used those fuel injector cleaners. I do my own oil change using Pennzoil platinum synthetic oil every 7500 miles and I flushed the coolant at 70k miles. So my car is pretty good on maintenance. The only thing left to replace is the rotors and pads due to warping.


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I am at 101,000 miles 2015 Mazda 6 sport. I recommend cleaning throttle body and maf sensor. I did it at 75,000 miles. It made a huge difference my throttle body was really dirty. I also recommend doing a drain and fill on the tranmission fluid.
 

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Here a YouTube link of video of a guy cleaning cx 5 throttle which is the exact same way our Mazda 6 is:

 

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Dragging brake(s), intake tract leak, injector problem... these are things to check when mpg goes down quickly and stays there, when we’re not just entering winter.
 

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Modern MAFs are almost impossible to successfully clean and should never actually get dirty, assuming you are using the OE airbox and filter. They are "hot surface" (rather than "hot wire") and it's very easy to damage them even with so-called "MAF cleaner."

If they're not working properly the only real fix is usually replacement. The throttle body wasn't the issue; the MAF may have been, but do expect to be buying a new one; cleaning them usually is unsuccessful over the long haul, especially the hot surface ones..
 

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Discussion Starter #15
Modern MAFs are almost impossible to successfully clean and should never actually get dirty, assuming you are using the OE airbox and filter. They are "hot surface" (rather than "hot wire") and it's very easy to damage them even with so-called "MAF cleaner."

If they're not working properly the only real fix is usually replacement. The throttle body wasn't the issue; the MAF may have been, but do expect to be buying a new one; cleaning them usually is unsuccessful over the long haul, especially the hot surface ones..
Tickerguy, I have checked the hubs of the brakes after driving them for a while, they are not hot at all, and oddly they are cool to the touch.

Damn, I wish someone in this forum lives near me who has a 3rd gen mazda6 and has the mechanical aptitude to effectively diagnose the root cause and fix it.
 

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Discussion Starter #16
Here a YouTube link of video of a guy cleaning cx 5 throttle which is the exact same way our Mazda 6 is:

Haha, I don't want to even bother disassemble the airbox and it's surrounding parts to get the throttle body. I would be likely to screw up one of the sensitive parts of the body if I was cleaning it or whatever.
 

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Cleaning the TB is a waste of time if your air filter works at all. All it does is throttle the air; it's not involved in fueling or metering anything, other than the air. Think about it.

Now the MAF, on the other hand, can very easily cause all sorts of trouble, and chief among them is poor throttle response and bad fuel economy, because it's what tells the ECU how much air is going into the engine and thus how much fuel SHOULD be injected (by its maps), which is then "confirmed" by the O2 sensor on the other end that you actually burned what went in (the oxygen was consumed.)

In many cases a bad MAF will not throw a code since it's quite difficult for the ECU to know that the reported value indicates a problem with the sensor. You can get an "implausible" code in some cases but a good percentage of the time you just get crappier performance and often crap fuel economy without any other warning. MAFs generally do not go bad PROVIDED your air filtration is up to snuff; the hot film ones, however, are quite-easily damaged by any sort of particulate or (much worse!) oil contamination. If you like buying MAFs then aftermarket intakes and air filters are a good thing to put on your car, in other words.....

BTW many if not most modern vehicles have digital MAF outputs; you cannot check them with a voltmeter as they return a digital signal. The only way to know what it's actually returning is to look at the PCM data, which in most cases is visible using something like Torque via the OBD port.

Most engines have a maximum published airflow; one way to test the MAF is to run a log at WOT all the way to redline on flat ground at or near sea level and see if you get a reported value at or very near that amount. If you get materially less than the published figure odds are high the sensor is bad. If you do it's probably working ok -- but not always. One way these do commonly fail is to limit out well below the actual maximum possible airflow.

A definitive test is to swap it with another identical car and see if the driveability problem disappears. In cases where you're seeing fairly extreme performance or fuel economy impacts you can unplug the MAF (engine OFF when you do it!); the car will run with the default fuel maps in limp-home mode (and WILL throw a code); if it runs BETTER with it unplugged than with it plugged in the MAF is definitely no good as there's no way that default map is superior in performance.

If you have a friend with the same car swap his MAF into your vehicle and see if the performance problem disappears (it will disappear IMMEDIATELY if the MAF is the cause.) If not then unplug it (car OFF of course when you disconnect it) and see if performance IMPROVES. Again, the change will be immediate if the MAF is the cause. If you do the latter you WILL get a check-engine light and code that you'll have to clear. If either restores performance then replace the MAF sensor.
 

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My Mazda6 has racked up 75,000 miles already, so in the past three months I have experienced power loss and the fuel economy is going down in the gutter. I'm getting like 20 mpg on highway and 15 mpg on city. I don't have any CEL. When, I push the gas pedal, there's a lot of hesitation in terms of acceleration, like pulling a boat or something, and sometimes it would buck back and forth. I did the maintenance such as changing the spark plugs at 75k miles (OEM plugs), changing the oil at 5k (Castrol EDGE Full Synthetic) with OEM oil filter (also I put the fuel cleaner [Chevron Techron] after each oil change, changed the air filter (OEM) at 75k miles, and cabin air filter too.

So, what is the issue? Is it in need of "fuel induction service" that the stealership keeps pushing me to buy? Or is the intake valve full of carbon deposits?
On this, I would hook it up to an OBD-II scanner and see if the ECM can tell you something. There are a lot of times that trouble codes will be present without triggering the CEL. I bought a
Zurich ZR-13 scanner from Harbor Freight a few years ago and it has a lot of features that have helped me with my cars over that time. Besides the features it also can 'read' a variety of cars.
For me, it works on my 2015 Mazda 6, 2001 Ford Ranger, and 2003 Porsche Boxster S. So I don't have to have multiple scanners. It is currently $190 at Harbor Freight. If that is a little expensive
and you have a Windows 7, 8, or 10 laptop or tablet, you can get a ELM327 OBD-II to USB adapter/translator and install software on your device that ranges from free to a couple of hundred
dollars. You can get more information via a web search for 'ELM327'.

The more information that you have, the better diagnosis you can make.

At this point, everybody is just guessing based upon their experience. For instance, I had an O2 sensor go belly up on a 1998 Saturn that exhibited the same symptoms that you describe.
The ECM had no input on how fuel was being burned. So it reverted to an open-loop condition that caused too much fuel to be injected into the cylinders. Hesitation on acceleration,
crappy fuel economy, etc. It may be a sensor, but I really don't know.

Ask the ECM. It'll give you better information than our SWAGs here.
 

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No, I have not cleaned both of things.. I don't know how to do it though
I have a 2004 Mazda 6s 3.0 liter stick shift and I am dealing with the same issues exactly I’ve also cleaned throttle body and Maf and no difference so I read obd code p3405 camshaft position sensor and so I changed it and no difference so I am confused to what I need to do next liana from California
 

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It is extremely unlikely that TBI cleaning and such will do anything.

Check your brakes -- carefully. Drive for a while then get out and feel (CAREFULLY!) the hub area; if you find a hot one (or more) you have a dragging caliper, which will do severe damage to your fuel economy.

It's likely also spark plug time, and also check your air filter.

That's where I'd start.
Yeah I also did coils plugs and Maf and throttle body along with camshaft positioning sensor and no difference I even replaced valve cover gasket at the very beginning to ensure my plugs were getting spark and there are no oil leaks I did oil and filter and nothing changed on my 04 Mazda 6 s and so any suggestions
 
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