Octane too high = stalling?

Kurt B · 01-06-2003, 11:08 AM

When cold. Or takes a while to get warmed up and not stall. I'm guessing based on my latest experience. No preignition whatsoever, but the idles funny and sporadically when cold.
My imagination? Confirm or reject this theory if anyone knows.

Emission · Emission's Garage

COLD in Los Angeles is what... 50 degrees?

I could only WISH to have too much octane in Southern California.

ttweed · ttweed's Garage

Hey- we've been down in the mid-40s overnight here in Lo Cal lately, at least before this latest Santa Ana started...

I don't see how octane rating of your fuel is going to cause your stalling problem. My guess is your mixture is not being enriched enough on cold starts. No experience with Motronics, but doesn't the head temp sensor tell the brain how much fuel the engine needs according to temp?

TT

Kurt B · 01-06-2003, 12:17 PM

Good point. I guess it could be the cold, but it was warm the last few days. It just seems to me that when the car is at running temp, and I bring it up to 5500 or 6k, and octane too low causes pinging, then it stands to reason that if I have the right mixture for those same conditions so it doesn't ping, the result might be that it's not explosive enough at low temp and low rpm to idle right. Maybe the DME has to adjust to the octane (it learns or whatever, about a few conditions)

That's my reasoning...and I'm looking for various opinions on it.

Rot 911 · 01-06-2003, 12:22 PM

Quote:

Originally posted by Kurt B
Maybe the DME has to adjust to the octane (it learns or whatever, about a few conditions)
That's my reasoning...and I'm looking for various opinions on it.

The Motronic DME in the Carrera's does not have a knock sensor or the ability to "learn" what octane gas you are using.

Superman · 01-06-2003, 01:00 PM

For current intents and purposes, higher octane gasoline should be recognized as LESS explosive than low-octane gas. Higher octane gas does not have any more power than its lower octane cousins. Octane is a measure of gasoline's tendency to detonate. Without a spark, gasoline will spontaneously ignite (see Island, I remembered) at a certain combination of heat and pressure. Higher octane gasoline requires a higher combination of heat and pressure.

So, bottom line....octane has nothing to do with your experiences. If your engine runs fabulously at temperature, and more poorly when cold (brrrrr, fifty degrees!), then your cold enrichment system is not working properly.