no, it's causing the engine to knock, the knock sensor picks this up and tells engine management to retard the timing causing a decrease in power. Increased octane fuel might be bringing it back to near normal conditions, all just a theory. I'm not saying this is what's happening to the OP, just an offshoot discussion about possibilities. Other reasons for knocking could be low fuel pressure, higher than normal cylinder temps, really dry air, etc.
no, it's causing the engine to knock, the knock sensor picks this up and tells engine management to retard the timing causing a decrease in power. Increased octane fuel might be bringing it back to near normal conditions, all just a theory. I'm not saying this is what's happening to the OP, just an offshoot discussion about possibilities. Other reasons for knocking could be low fuel pressure, higher than normal cylinder temps, really dry air, etc.
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I don't think it's knocking or retarding timing, or an ses light would have occurred by now, if op could actually hear and feel these processes.
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CX5_Pete
I've been going back and forth between 91 and 87 for the last 4 tanks. So far I can't say if it does make a huge difference. I think with the 91 it might have been more responsive, but it's hard to say. As far as gas mileage goes, I still average about 32 MPG on both. I am a bit disappointed, though. I thought I would be able to hit at least 34-35 MPG, but it is still pretty good for a CUV I suppose. The RAV4 I had as a rental for the week averaged about 29 MPG. Then again, I rev the piss out of the 2.0 driving around in the city cause it is so rev happy and the wonderful exhaust note that fills the cabin as the engine sings past 4,000 RPM puts a big smile on my face. On the highway I keep it civil and stay at 70 MPH.
If you switch each fill up, the octane rating of the fuel in your tank probably fluctuates between 88 and 90 since there is probably 2+ gallons of gas left in your tank each time you get gas.
The difference isn't "huge", but some do see a small difference in how the engine sounds and in how smooth the torque curve feels at high temperatures.
To see the difference, run 87 octane for a few full tanks before trying a tank of 91 octane.
Accelerate to 43MPH, shift to 6th gear (43MPH is the recommended shift point into 6th for cruising) and try to accelerate.
With 87 octane, my CX-5 just won't feel happy and you'll want to downshift.
With 91 octane the engine happily and smoothly pulls me forward.
Mine has been like this since new, so I don't think deposits play a role here.
On the skyacitv engines, knock (abnormal combustion) is not really an unusual event. It's just another piece of basic information that the ECU uses to control the motor.
C
CX5_Pete
If you switch each fill up, the octane rating of the fuel in your tank probably fluctuates between 88 and 90 since there is probably 2+ gallons of gas left in your tank each time you get gas.
The difference isn't "huge", but some do see a small difference in how the engine sounds and in how smooth the torque curve feels at high temperatures.
To see the difference, run 87 octane for a few full tanks before trying a tank of 91 octane.
Accelerate to 43MPH, shift to 6th gear (43MPH is the recommended shift point into 6th for cruising) and try to accelerate.
With 87 octane, my CX-5 just won't feel happy and you'll want to downshift.
With 91 octane the engine happily and smoothly pulls me forward.
Mine has been like this since new, so I don't think deposits play a role here.
On the skyacitv engines, knock (abnormal combustion) is not really an unusual event. It's just another piece of basic information that the ECU uses to control the motor.
I agree with this somewhat. I have this hill that I hit on my commute. Usually I have to downshift from 6th to 5th as the engine couldn't hold 6th even with full throttle. With the 91, it seems to hold it a little bit longer and actually makes it to the peak. Having said all this though, here premium is usually $0.20 more per gallaon and I just can't justify the cost.
I'm in the same boat. I'll only get premium if it's hot out and I really want the car to perform as well as it possibly can.
The $2.50 per tank is better spent on beer 95% of the time.
Hmmm, that's interesting. The last time I put 11 gallons of premium in (by accident), I noticed the engine seemed slightly less peppy (slower) and that tank returned less MPG than the 4 previous tanks and 17 tanks afterwards. All tanks were 87 octane except the one Premium tank that had lower mpg's. Yes, the 11 gallons of premium were blended with 4 gallons of 87 but still, it felt less powerful.
I'm not convinced my knock sensor has EVER detected knock. Keep in mind "abnormal" means "not normal" which is a synonym for "unusual". Maybe your California gas is different than what I get up here from the local refineries.
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CX5_Pete
Our gas (California) is special. So special we get to pay at least $0.50 more per gallon compared to the neighboring states. In some areas I saw gas was still close to $3/gal! But those are usually on the west side close to beach cities.
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I put 91 octane in my tank the other day. So far, I am getting identical mileage to 87.
WA state has a gas tax around $0.45/gallon IIRC.... today I filled up CX-5 at Costco north of Seattle and paid $1.66/gallon for regular.
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CX5_Pete
At my Costco 87 was $2.059. I haven't seen it this low in a long time.
Well, no.
The engine parameters are dictated by things like temperature, barometric pressure, etc. The systems strategy is to use parameters that won't cause knock as long as the octane is at least 87. So, yes, the engine management will dial back timing when it's extra hot but it will do that whether you have 87 octane or 93 octane. The knock sensor is a fail-safe in case your fuel doesn't meet the 87 octane spec or a sensor is out of whack and returning inaccurate readings causing knock. Your check engine light will come on and an error code will be stored and the engine power will be reduced so you can safely drive to have the issue diagnosed.
If you live in the Rocky Mountain states, do not use 85 Octane due to the altitude. The engine management system KNOWS you are at altitude and will compensate for it. By putting 85 octane in you would be double-compensating. This is not a "dumb" car of yesteryear when the high altitude/lower octane rules of thumb were developed.
I don't think that's right.
http://www.mazdas247.com/forum/show...D-s-for-CX-5&p=6254804&viewfull=1#post6254804
You might find this quote interesting:
Piotrek, you are misinterpreting the info contained in that post. It actually supports that the ignition is retarded the same amount regardless of octane 87 or octane 91. Read it again:
Notice that his data reader reports the same amount of knock retard regardless of the octane. Knock retard (KNOCKR) is simply a value (in degrees) that is applied to the base ignition map to AVOID knock. It does not imply that knocking has already occurred. When knocking occurs an error code is stored in memory, the check engine light illuminates and a new, more conservative correction factor is loaded to allow you to continue driving without knock.
The KNOCKR value is calculated based on the amount of air that was taken into the cylinder (not from knock sensor data). The amount of air in any given combustion event is a function of valve timing, throttle plate position, barometric pressure and temperature and is measured in a variety of ways but octane is not considered (because the engine management system does not attempt to guess the octane).
Check engine light usually comes on only when there is a malfunction such as a bad knock sensor. Engine timing is always being adjusted (retard/advance) as the ECU sees fit according to engine sensors without throwing a code. I can understand where a constant knocking will set something off but knocking that occurs once in a while shouldn't throw a code. Where did you get this from?
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It's true that ignition timing (not engine timing) is always being adjusted to avoid knock. The primary adjustment to avoid knock is based upon data from sensors such as air temperature, barometric pressure, MAF, MAP, etc. The knock sensor only comes into play when knock unexpectedly occurs. This is in contrast to the recently announced Skyactiv turbo which will adapt to fuels of different octane using the knock sensor to adjust timing to suit as a normal part of it's operation. It will constantly try to advance the timing as far as possible without knocking.
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And if it makes it into the CX-5, will be a real winner!
