uprev wrote:Just to be clear, I'm not trying to throw a monkey wrench into the whole deal.
Fact of the matter is the way the Nissan and Infiniti ECU works is that it measures parameters and adjusts itself based on data it gets from sensors. There are very few static settings in the ECU. Most of the data it runs its routines on are look up tables and the way it calculates its outputs are based on numerous tables from different points of input.
You have some tables that are target guidelines and some that are corrections. No single adjustment is made without referencing a number of different tables. The ECU learns by way of adjusting to hit its given targets. If it cannot reach those targets, it is often because of another table that limits the corrections allowed.
Timing and fuel corrections in the ECU that would be directly affected by changing your Octane rating may also need to reference a given load, calculated or predetermined and it may not be able to adjust because from the factory it was designed to use a certain octane level and Nissan limits those references for safety purposes.
On the G/Z cars the ECU is set (in north american markets) for 91 Octane fuel. The trucks are all set for 87 Octane. Using 91 Octane in the G/Z will obviously cause the ECU to adjust itself, and it will try its best to cope with it. The primary means it has is the high det ref table. If you add load to the motor while running lower octane fuel, you will come up against detonation. The ECU will compensate quickly for this by using the high det table timing references and it will lower the timing to a more safe setting temporarily. It however will not change it for the rest of the time you own the car, it is very temporary. This does not change drastically over time, contrary to what people think, it is not learned. It happens very quickly and hopefully that reference table on your particular car works well enough to cause it to stop detonating. You lose power and economy when this happens.
Now that said if you never go up a hill, or carry 4 people in your car, or accelerate quickly, you might just be safe. The only way to change this is to get a tune designed for your car with low octane. That way those reference tables are changed and you don't have issues with load.
Realize that timing is done based on fuel burn rates, and peak cylinder pressures. If you don't use the recommended octane, the fuel burn rates change, and the ECU doesn't change to match that. So your timing will be off no matter what argument you wish to make about it. This is part of the code running on every ECU.
The same goes for the Truck owners that want to run premium fuel. It is better for the motor (the higher octane helps keep the cylinders cooler and less chance of detonation under load), but you really won't see any power gains unless you adjust the tune for the higher octane.
uprev
Thank you for your input
What I am trying to prove is that for the two thousand miles a month that I commute, regular 87 octane is fine?
There are no hills, just flat New Jersey Turnpike and Garden State Parkway 50 miles each way usually on cruise control on the way in and not on cruise control on the way home.
I have 3 1/2 years of records of every fillup. There are a gazillion threads on gasoline so I agreed to this experiment. I filled up yesterday with 93 octane for the first time with 85k miles on my GI will use 93 octane for about a month calculating my MPG with each fillup. First results should be Friday with about 300 miles on my Tuesday fillup.I will repeat the test next month with 91 Octane for about another month.My feeling is the extra expense versus regular is probably not worth it but we shall see
Telcoman
