Live Data From The Saturn

[The Critic]

Here is some live data from my Saturn's onboard computer.

The vehicle is a 96 Saturn SL2 with 143,000 miles. The Thermostat is a 195F unit. I currently have a mix of 11 gallons Costco 91 octane fuel and 2 gallons 87 octane in the tank, if that matters. There is also a few ounces of Amsoil PI left in the tank as I have just finished a treatment.

I am confused as to why the spark advance is in the negative. More specifically, why I have 14 degrees of negative spark advance at idle. Is this normal? Or is it something bad? Could it be due to the high octane fuel I have in the tank? The car specs 87 octane, but I am running 91 as a test.

Also, in my OnDemand5 reference source it shows that for Oxygen Sensor testing, 0.1 volts equals lean and 1.0 volts shows a rich condition. Mine is showing 0.270 volts, so is that good or bad?

And for the STFT B1 value-- is that the long-term fuel trim?

Thanks.

 

[Colt45ws]

Oxygen sensors constantly switch between lean and rich. It occurs way to fast for you to watch the computer output. You would have have to use a scope to see. The post cat sensor will switch slower. It will also be more gradual of a curve; less amplitude. I have a pic somewhere Im trying to find... This is how the computer looks for a failing cat, if the switching speed approaches that of the forward unit, it pops a P0420.
Being less than .4v it means the engine was lean at the specific snapshot. The computer would then add a bit more fuel next go around and get a different number. More than .6v is rich. It ignores .5v, thats near stoich, so those numbers get thrown away.
Ive never gleaned any useful information from watching spark advance. It takes so many variables into account to come up with the advance it wants its hard to exactly duplicate conditions. I suppose if you could datalog it so you can see trends you might be able to see what its doing. Do you know if it has a knock sensor? If it does not it wont be able to tell you have more octane and its doing the same spark it would do with any other gas.
STFT is short term.

 

[The Critic]

Originally Posted By: Colt45ws
Do you know if it has a knock sensor? If it does not it wont be able to tell you have more octane and its doing the same spark it would do with any other gas.
STFT is short term.

Yes, it does have a knock sensor.

 

[Colt45ws]

Yeah, Ive watched spark on my car with the scangauge and tried different octanes. I couldnt tell anything since I am unable to exactly replicate all the conditions it takes into account. If you could data log it you might be able to tell where its trending, though.

 

[Colt45ws]

Here.

 

[JHZR2]

Looks like what my scangauge reads out, but with sensor voltages.

Ive seen ignition go negative (though not that negative) at idle on all my vehicles. Then it goes positive to >30 when driving.

It only seems to go negative at true idle (not foot off throttle coasting in gear).

 

[The_Jeff]

The true test, and not part of the unencrypted OBDII bits, is knock retard. Doubt your scan tool shows it.

Apples to Kumquats, but I can squeeze 31-32 degrees of advance out of my SOHC saturn at incredibly light throttle and highway speed. Amazing how another degree of pedal travel pulls timing into the lower 20s.

 

[IndyIan]

Originally Posted By: eljefino
The true test, and not part of the unencrypted OBDII bits, is knock retard. Doubt your scan tool shows it.

Apples to Kumquats, but I can squeeze 31-32 degrees of advance out of my SOHC saturn at incredibly light throttle and highway speed. Amazing how another degree of pedal travel pulls timing into the lower 20s.

I don't think I've seen negative advance on my cars, my parents CRV showed -8 deg on my scangauge.
I think its how the advance range is setup in the computer or what they define as 0 advance. Is 0 actually spark at TDC or is 0 spark at 10 deg before TDC but with zero computer adjustment?
Both my cars see advance as high as 40-41 deg with a light pedal and rpms around 2800 but they idle at 10 or 12 deg, not zero.