I heard something interesting this weekend and was hoping someone out there could verify... heard that the S197 ECM will automatically remap fuel and advance timing if higher octane fuel is detected.. is this true? Required running 87 fuel tank empty, then filling up up 91 (or 93), disconnecting battery (15min), then restart. Will ECM continue to push timing up a few degrees without a reflash (thus generating a few more HP)?

 

no it will do nothing, maybe even cost you half a pony

 

The only thing you could benefit is the guarantee that the engine won't pull any timing due to knock sensors. If you are running 87, it is always possible to get a little bit of spark knock, causing the sensors to pull some timing, costing some power. Running 91 will virtually guarantee this won't happen. But, I don't think it will ADD any HP that wasn't there before.

 

There is no sensor that I am aware of that will detect the octane rating of the fuel that you are using and advance timing all on it's own. Maybe someday when we have flying cars

The CPU can only deal with what it knows, and from the factory it knows it has to run on 87 Octane.

 

I agree. In fact, when I go racing I let my tank get down to about 2-3 gallons or so of 91 octane pump gas, and then add about 2.5 gallons of 110 octane to it. So, I get an effective octane of around 100 (give or take a couple). But, since I'm still running my everyday 91 pump gas tune, I don't expect any power gains from it. What I get is anti-detonation protection. Even a "bullet proof" motor can get seriously hurt by detonation.

 

Mine runs noticeably better on the stock tune with 93, and I get about 2.5-3 mpg more than 87. I thought this was normal for these cars. I have tested this several times as my drive is nearly precisely the same everyday, and the exact same test in my '02 showed no difference between the 2 gasses (before tuning).

 

Interesting. I will try this experiment myself next fill up. I have a perfect drive to work each day, ~30 miles one way of interstate at 75 on cruise.

 

Normally I use 95RON because it's the lowest octane available here. A couple of years ago, before any mods (i.e. no tune, CAI, etc), I was in Germany and filled up with 100RON just out of curiosity. Although I had no proper means of testing the difference, the SOTP meter showed no improvement.

 

you need to advance the spark timing to get any benefit out of the extra octane

 

the rumor is that the stock tune is actually set for 93 octane and it uses the knock sensors to reduce timing and allow 87 octane. There have been a couple of dynos that have shown an increase of a few rwhp with 93 octane on the stock tune and no other mods.

normally, you guys would be absolutely right of course.

 

Thx for all the replies.. that was basically my question. Since I've been running 87 since day 1, was curious if the ECM went into 'adaptive learning' mode, and lowered my timing. Now, if i put in a higher octane, will it 're-learn' (i.e, does not sense knock-sensor reads) and increase timing... or does the ECM consistently have timing set high (as you indicate for 93) and just retard it if it senses knock?

 

On hotter days you can hear it ping a couple times here and there a millisecond before the computer adjusts on 87. I switched to 89 and it never does it anymore.

 

I wouldnt doubt that these cars were meant to run 89 or 91 stock. Mine does seem to run better on 89 or 91. I am going to be tuning mine to 93 this week once the tank is empty.

 

for me its simple. 87 is fine. there is a good knock sensor on our cars though. to properly adjust the timing the car needs to feel a slight knock first