Re: Terrible mileage 99 GLE

Ralph Hertle wrote:
> Dave:
> 
> David Geesaman wrote:
> [...]
>> I've done two years of serious research tracking my fuel economy.  I 
>> used only 93 octane for several years before switching to 89.  My fuel 
>> economy did not change at all.
>>
>> I imagine under very heavy load there is a difference, but for routine 
>> driving you will not see anything.
>>
>> Dave
> 
> 
> The higher octane rated, or equivalent to chemically pure octane, has no

> benefit to power at all. Nor is there a difference in the quality of the

> product. The octane rating numbers have nothing to do with quality or 
> power produced.

No, not directly.  But you're missing the point - the Maxima has a knock 
sensor, and if it detects engine knock it will retard timing to avoid 
further engine knock.  When running on retarded timing it will have 
lower power, and many have re****ted lower fuel economy.

 > The computer makes the ignition delays, and other changes to 
induction > timing and fuel metering, etc., and you may not be aware of
the
 > changes made to the engine functions to avoid the knocking.

Yes, this is the reason for my post.

Early on I checked my ECU codes for the ghost code that indicates the 
ECU has retarded the timing due to knock sensor feedback.  Of course, 
the actual fuel economy numbers are further evidence.  That's the point 
- I want to run the lowest octane fuel that does not trip the ECU into 
conservative timing maps.

> Ralph Hertle