Miatas and premium versus regular gas

josh wrote:

> Funny how I can't really find much info on the operation of this thing
> on the net.

The temperature sensor is most likely a temperature-variable resistor,
also called a "thermistor".

You can probably gain some insight from looking at the Megasquirt
EFI page or perhaps at Dick Bipes' ACU documentation.

Cheers,
Dana

josh > wrote:

>Leon van Dommelen wrote:
>> josh > wrote:
>>
>>
>>>Larry Gadbois wrote:
>>>
>>>>Josh,
>>>>
>>>>The '99 and 2000 Miatas engines are the same.
>>>
>>>Yes that's what I figured.
>>>
>>>But of course I did drive a number of '99s (with low miles... under 15K)
>>>before I drove MY 2000 model, and my car was decidedly more peppy... very
>>>noticeable.
>>
>>
>> Strange. Do you think the knock sensor could be broke?
>
>Well it doesn't regularly knock on 91+ octane gas. You have to really TRY
>to get it to knock (5th gear 20mph WOT).

I too have no information on what exactly this thing does or think
it does, but it has been suggested on this group that the advance was
not very aggressive. Mazda might have designed the engine control
for 91 octane, relying on the knock sensor to take out timing if
that proves too aggressive for 87 octane.

Retarding timing by sensing knock is not a very reliable procedure,
because when it knocks audibly, you probably already have glowing
carbon deposits causing it, and making things worse.

>IDK exactly how the knock sensor works on a NB but if it's like other cars I
>have experience with, then it's a piezoelectric element embedded in some
>kind of casing bolted to the block in a certain spot. Failure mode would be
>disconnect (which would cause an error code, likely retard timing, engine
>light come on), wiring/connection flakiness (intermittent engine light),
>overtorqued/cracked element (constantly sense knock, car would run like
>total crap and retard the timing), or undertorqued or the thing is defective
>in a way that it never senses knock, in which case you'd think it'd knock
>all the time no matter what gas.

I would not. As a supercharger owner, I know 91 makes a big
difference in whether it knocks or not compared to 87.

Leon

--
Leon van Dommelen Bozo, the White 96 Sebring Miata .)
http://www.dommelen.net/miata
EXIT THE INTERSTATES (Jamie Jensen)

Leon van Dommelen wrote:

> I too have no information on what exactly this thing does or think
> it does, but it has been suggested on this group that the advance was
> not very aggressive. Mazda might have designed the engine control
> for 91 octane, relying on the knock sensor to take out timing if
> that proves too aggressive for 87 octane.

My 2002 SE, pre-JRSC, would ping slightly under WOT@3k RPM, like when
climbing a steep hill in a low gear at low speed. I think the motor
probably needs genuine 93 octane to avoid knock/retard.

Dana

Leon van Dommelen wrote:

> I too have no information on what exactly this thing does or think
> it does, but it has been suggested on this group that the advance was
> not very aggressive. Mazda might have designed the engine control
> for 91 octane, relying on the knock sensor to take out timing if
> that proves too aggressive for 87 octane.
>

So you're saying that the ignition advance provided by virtue of input from
the intake air temp thermistor is not very aggressive? Or the timing curve
is not too aggressive on the whole? Frankly I have no clue what the ECU
function is but if this intake air temp sensor has much of an effect on
timing advance I'd be surprised, particularly in comparison to the input of
a knock sensor (or four). My guess is that the ability of the ECU to retard
the timing is insufficient to prevent knock on 87 oct. gas given whatever
other combination of variables and tolerances on my particular car. I guess
a timing light would settle it once and for alL!

I'd think the air temperature in the tract between the air filter and the
throttle is reasonably consistent and exact location of this sensor should
not make a really big difference in running of the car. Certainly it can't
be sensing anything very fine... 10degF or larger resolution? Hard to say.
Mainly the only thing different in my car is where this component is
located in the intake plumbing. I guess it's possible it's getting an
erroneous reading.

FWIW I found some notes... I put this intake in with 600 miles on the car.
So having not broken it in 100%, there's no way to recall whether it truly
"always knocked" or "always since I did the intake mod".

In article <1112802547.638935@sj-nntpcache-3>, josh >
wrote:

> Frankly I have no clue what the ECU
> function is but if this intake air temp sensor has much of an effect on
> timing advance I'd be surprised

I don't know much about NBs, but I'd suspect the sensor affects mixture,
not timing. Of course, being too lean can cause pinging, too.

--
Lanny Chambers, St. Louis, USA
'94C
the alignment page:
http://www.hummingbirds.net/alignment.html

josh > wrote:

>Leon van Dommelen wrote:
>
>> I too have no information on what exactly this thing does or think
>> it does, but it has been suggested on this group that the advance was
>> not very aggressive. Mazda might have designed the engine control
>> for 91 octane, relying on the knock sensor to take out timing if
>> that proves too aggressive for 87 octane.
>>
>
>So you're saying that the ignition advance provided by virtue of input from
>the intake air temp thermistor is not very aggressive?

I was talking about the knock sensor, but on the link ECU's, ignition
is retarded when the intake air temperature increases too. But as
Lanny says, the problem with having a nonstock intake might be too
cold air for the amount of fuel supplied by the ECU, giving a lean
mixture. The stock airbox takes in warm air at a regulated
temperature.

> Or the timing curve
>is not too aggressive on the whole? Frankly I have no clue what the ECU
>function is but if this intake air temp sensor has much of an effect on
>timing advance I'd be surprised, particularly in comparison to the input of
>a knock sensor (or four). My guess is that the ability of the ECU to retard
>the timing is insufficient to prevent knock on 87 oct. gas given whatever
>other combination of variables and tolerances on my particular car. I guess
>a timing light would settle it once and for alL!

I should have somewhere the Link ECU timings for the nonaspirated
1.8l engine.

>I'd think the air temperature in the tract between the air filter and the
>throttle is reasonably consistent and exact location of this sensor should
>not make a really big difference in running of the car. Certainly it can't
>be sensing anything very fine... 10degF or larger resolution? Hard to say.
> Mainly the only thing different in my car is where this component is
>located in the intake plumbing. I guess it's possible it's getting an
>erroneous reading.

Sure. It could be heated by a variety of problems (boundary layer
air, heat conduction through the conduit, radiation, etc. But IIRC,
you said that your plugs did not show evidence of a lean mixture?

Leon

>FWIW I found some notes... I put this intake in with 600 miles on the car.
> So having not broken it in 100%, there's no way to recall whether it truly
>"always knocked" or "always since I did the intake mod".

--
Leon van Dommelen Bozo, the White 96 Sebring Miata .)
http://www.dommelen.net/miata
EXIT THE INTERSTATES (Jamie Jensen)

(Leon van Dommelen) wrote:

>I should have somewhere the Link ECU timings for the nonaspirated
>1.8l engine.

Come to think of it, that is for the M1 compression ratio.

Leon

--
Leon van Dommelen Bozo, the White 96 Sebring Miata .)
http://www.dommelen.net/miata
EXIT THE INTERSTATES (Jamie Jensen)

Leon van Dommelen wrote:

> Sure. It could be heated by a variety of problems (boundary layer
> air, heat conduction through the conduit, radiation, etc. But IIRC,
> you said that your plugs did not show evidence of a lean mixture?
>

That's right.

But I haven't had them out in 30K miles. Worth it to check that too. The
orig. plugs just had regular looking plug wear and were nice and tan.

Ok here's a different view I bought my 1990 Miata last April specifically
with the intent of summer drives and autocrossing it every chance I get. The
car had a Jackson Racing supercharger on it when I bought it which requires
and or specifies 93 octane which is hard to get. So I have 2 marks on the
crank sensor 6 btdc for 91 and 8 btdc for 93. A friend asked me what kind of
mileage I get my answer was "Who Cares" I did not buy the car for milage.
"Larry Gadbois" > wrote in message
nk.net...
> There are a lot of differences of opinion on this issue. Mazda designed
the
> 2001 and new MX-5s to run on 91+ octane gas.( I don't think you need 104
> octane gas!) Mazda design engineers know which fuel octane will provide
the
> best performance and reliability for the car. Your MX-5 has a knock
sensor
> that retards the timing when knock is detected, to prevent possible engine
> damage. Running a octane gas that is lower than recommended may reduce
your
> effective miles per gallon and also reduces engine torque. It also causes
> increased engine temperatures that could cause damage when driving in
> extremely hot summer weather.
>
> I passed a '97 Eldorado yesterday with the 4.6L Northstar motor. These
cars
> have a knock sensor also, but I could easily hear the "pinging." Why would
> someone spend that kind of money for an automobile and run it on 87
octane?
>
> Another approach to saving money on gasoline is to adjust your driving
> style. If you are getting only 20 to 24 mpg on your car and you need to
make
> your money go further, it makes more sense to use the right grade of
> gasoline, and reduce the hard throttle starts and high rpm shifting that
> burns more fuel.
>
> The older '89 through 2000 Miatas were designed to run on 87 octane. I
> average about 26 mpg in combined city/freeway driving on my '99, and that
> includes some spirited driving. Running higher octane than recommended
does
> not increase power or miles per gallon on any stock MX-5.
>
>
> "Boris Goldofski" > wrote in message
> news:71n3e.146153$gJ3.121513@clgrps13...
> > What are the opinions of Miata drivers about premium versus regular gas?
> > I
> > have babied my 2003 Miata with 104 octane premium, but with present gas
> > prices I wonder if this is worth it?
>
>