Effect of low octane gas?

boostisgood said:
Ohhh educate me please. Or how about I educate you.

First, you have 2 types of Oxygen sensors in ODBII cars.

1. Zirconia sensors, which produce a reference voltage on thier one (Between 0mV to 1000mV with 450 mv being Stoichiometric) it compares the oxygen content of outside air which is 21% to the content of the exhaust. This is to allow the PCM to go rich/lean rich/lean so the Catalyst will operate properly and burn off the NoX and produce the water and C2O for emissions.

2. Titania sensors. They do not produce a voltage but act as a normal sensor in your vehicle and return a reference voltage back to the PCM (resistance type sensor). This sensor ACTUALLY detects the ammount of air in the exhaust and returns the signal voltage to the PCM. It does not use outside air to compare.

What your front oxygen sensors do is called cross count. It will go above and below .450 V (again that is stoich) and feed that info to the pcm so it can ad and take away fuel as needed for emissions.

now with that brief explanation of Oxygen sensors (and toyota uses a 5v in some cars) I will now ask you these questions.


1. Are you a tech or an engineer of PCM programs?
2. If you are and use a scan tool (Genysys Snap on red brick or OEM like the ford/mazda WDS) do they show what the octane rating is along with the data streams of the sensors? Ill actually answer that one for you NO THEY DONT. Now if the octane rating is that important, wouldnt you think that if the PCM was capable of determining the rating via what the sensors are sending it, it would ? Case in point, when my engine blew, Mazda could not gather the info on the type of gas in my car based on PCM/ECU data provided nor from the freezframe info from the CEL. If the PCM could determine it, should it not have been displayed ?


I could go on forever, but I would rather go play with my kids now.
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What are you talking about? You answered your own question. A O2 sensor reads the oxygen content in the exhaust stream. Period, end of story. The Oxygen content, nothing else. It doesn't matter what sensor you use.
If it knows everything going in the motor, it knows what it should see coming out. By changing the octane rating of the fuel going in, it changes the oxygen content coming out. It's that simple. I did not come up with this crazy notion one day. It was all explained to us at the Mazdaspeed6 tech. training. On top of that if you went to Engine Management Level 2 class by Vw you would also learn this (New Vw's do the same thing).

Also I assume you mean you blew a MSP motor, totally different pcm's going on here.

And with the pcm's in the Mazda6 and Speed 6 you can determine the octane reading...sort of. Using a new pid called rear fuel trim. It gives you a value that can help you determine whether the correct fuel is being used.

You do not need a egt sensor to read the temperature of the exhaust.
 
BlkZoomZoom said:
What are you talking about? You answered your own question. A O2 sensor reads the oxygen content in the exhaust stream. Period, end of story. The Oxygen content, nothing else. It doesn't matter what sensor you use.
If it knows everything going in the motor, it knows what it should see coming out. By changing the octane rating of the fuel going in, it changes the oxygen content coming out. It's that simple. I did not come up with this crazy notion one day. It was all explained to us at the Mazdaspeed6 tech. training. On top of that if you went to Engine Management Level 2 class by Vw you would also learn this (New Vw's do the same thing).

Also I assume you mean you blew a MSP motor, totally different pcm's going on here.

And with the pcm's in the Mazda6 and Speed 6 you can determine the octane reading...sort of. Using a new pid called rear fuel trim. It gives you a value that can help you determine whether the correct fuel is being used.

You do not need a egt sensor to read the temperature of the exhaust.
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dealer techs dont know s*** except whats handed to them in a manual or learned at "new car coming this is whats wrong and how to fix on our campaigns"

Second, you NEED AN EGT gauge to know the EXHAUST GAS TEMPS. Oxygen content or lack there of does not give exact Gas temps.

GAS or the volitility does not control the ammount of O2 in the gas, AIR controls that. the actual combustion and ammount of fuel and air put into the engine controls the ammount of air coming out.

So you have now went from saying it KNOWS the octane rating to it SORT OF based on what the rear O2 sees ? you contradicted yourself there bro.

Dont argue with techs unless you are a tech yourself bro. :D

(I really am not trying to be a jerk man, just dont want wrong info put out to people is all)

Also, I dont know Vdubs so I cant answer ya there.
 
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he IS a mazda tech. You shouldnt act so high and mighty. Its not like what he explained wasnt feasable.
 
I am not trying to act all high and mighty. I just hate wrong info put out to people. (BTW I am a tech myself and in ADVANCED ENGINE PERFORMANCE RIGHT NOW)
 
I am done arguing with you. You are right and I am wrong. The Head Mazda Trainers in the country know nothing and were feeding me bulls*** just so you could prove me wrong by telling me two different types of oxygen sensors..


I am a Mazda Tech, Vw Master Tech, Ase Master certified.
Graduated almost top of my class at UTI, and re-built my first car at 15.

How does any car read the Cat. temperature without a Egt? Every ODB2 car reads it, but most do not have a Egt.

Octane controls the burn time of the combustion. The more delay you have in the combustion the more oxygen is going to make it out without burning.
 
it just sounds like you are. thats all. how is what he said wrong? your saying thers no calculation or amount of sensors that can guess at if you have the wrong octane? I dont buy that. he never said it tells you the octane, he said it tell if the octane isnt what its supposed to be. I dont think its an overly complicated thing for an oem ecu to do... but im not a tech.
 
BLKZM. Not gonna argue anymore either. No disrespect towards you at all man.

All Im trying to say is this, a PCM does not know the octane rating of the car based on sensor inputs from what I have learned and seen myself.

What you have learned from the guys that spread the word of the mazda engineering gods, I dont know. If something new has come out, I have not seen it yet.

as far as explaining the O2 sensors, that was without knowledge of ya bein a tech and felt that the explanation of the sensors would help.
 
Lets end it this way. The Mazdaspeed6 can determine the octane reading of the gas used. Now whether I convinced you how it determines it or not does not bother me. That is how it does it.
 
ok ok I will concede. I can see, based on what you explained, how it is possible. I just have not seen it for myself and will see what I can get on Monday.

Its always best to learn as much as possible in our field.
 
So if you use Octane booster say 103; would it incresingly make the car quicker? Or is it programmed to only accept as high as 93 or 91? (depending on the state.)
 
Correct. It will only do what it is programed to do. Using a Higher octane fuel will slow it down, but not to the effect a lower octane will.
 
Can you explain why using say Race gas of at least 100 octane will slow down performance? My car always felt like it performed better with it, but without data to support that, its just flapping. So I am curious to know why it has a negative effect.
 
It slows down the burn rate. If this is slowed down without need it is just a waste. The slower the combustion, the less oxygen is burned thus lower power will result. I do not know how much will be lost, it will be determined on the set-up. I have heard it is noticeable on a dyno though.
However, it depends on what the car is set up for. If you tune for the race gas then more power will result.
 
What he said again. If mazda didn't have the wds you could tune it yourself with the help of programers and a Xcal2. also not to fuel the already lit fire but I got cels from my intake but when my engine threw 2 pistons I didn't even get a cel and the car was running for a good 9 seconds afterwards. Moral of the story is Low grade octane in Hi octane rated/Hi perfomance vechicle=Bad don't do it :)
 
Da 6 said:
what he said...can't detect an exact octane rating but can detect wrong fuel and then lets you know you using the wrong fuel. As for not telling you it's marked somewhere. My car has it under the fuel gauges"Remium Fuel Onlt" but other companies put it on the inner gas cover. not shure where they put it on the speed 6. If someone could, please snap a pict :)
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Don't need any pix. I've known it needed premium since I read the first review way back when. Thanks to info in a previous thread, I suspected that the clowns at the dealer prep station DIDN'T know and put in regular before handing the car off to me, DESPITE the label inside the fuel door. I started this thread to get more info re: the wastegate for when I talked to the dealer.

Anyway, I'd like to thank everyone for the full and complete edyookayshin on PCM vs. wastegate. (deadhorse
 
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most dealerships do that and wonder why people won't buy the Hipo cars when they fail to perform better than the non Hi po version at a cheaper price. Neon R/T was one of those cars that couldn't sell cause they put 87 in it. At least the dealership admitted to it :)
 
Da 6 said:
most dealerships do that and wonder why people won't buy the Hipo cars when they fail to perform better than the non Hi po version at a cheaper price. Neon R/T was one of those cars that couldn't sell cause they put 87 in it. At least the dealership admitted to it :)
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Yeah, I was kinda shocked that they admitted it so quickly. Best in the long run for them, I think, since they lose trust and reputation when they try to hide/deny/etc.
 
about using higher octane fuels and power:

As mentioned earlier, higher octane fuel burns slower that's why it's more resistant to pre-ignition / detonation. To extract more power out of it the ignition has to be advanced to provide a longer burning time before the exhaust stroke. If the PCM is programmed to maximum safe ignition advance with 93 octane, then using higher octane may slightly reduce power because it will burn slower and less power will be extracted. At the same time it will provide a bigger margin of safety against detonation; that's why even though my RX-7's ECU is programmed for 91, I always use 93 or 94.

Now, some cars will continue to advance timing until detonation is detected, in these cases 100 or 110 octane race gas will provide more power.
 
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