Can you run rich but suffer detonation due to too low octane

[douglas vincent]

I am going to assume the answer is yes but let me desribe my situation.

I had a hidden boost leak/vacumn leak which I kept missing and instead kept fixing/upgrading everything else. I installed new plugs, magnecor wires, battery and battery connections, MSD DIS-4 (not the 2 cause it was free), and cleaned the air filter and cleaned the MAF element.

Now the car ran better but I still had the boost leak which was showing up as hesitation and bogging. basically it was a giant vacumn leak.

Now with all the electrical upgrades, the wagon obviously would run better but since I was never able to get up to full boost (even though sometimes it seemed like it according to the boost guage), I never go the compression up to a stage where I would suffer detonation.

Now last night, after a fun but dissapointing session at PIR, I finally found and fixed the boost/vacumn leak (bad hose connection under the AWIC. Bingo Bango Bongo, full power captain! Along with some nasty ping. But my AF ratio if fine and rich.

I had been running all day on 95-96 octane so this may have had the ecu tricked.
I also had just refilled the tank with 92 octane.
I went back the shop and poured the last 3-4 gallons of 100 octane into the tank and the pinging stopped.

So is it my upgraded electrical causing my detonation or my ECU being used to the higher octane for the day? Or a combination of both? If its the ECU, would resetting it drop the timing back to stock?

Thanks.

[vrg3]

Okay, a couple things:

1) The voltage from a narrow-band oxygen sensor can't really tell you whether or not you're running sufficiently rich.

2) You were running much more rich when you had the boost leak than you are now, because you still got fuel for all the air that escaped through the leak.

3) Chances are slim that your ignition upgrades are contributing to detonation. Some people do feel that MSD ignitions can lead to pinging because of the multiple sparks at low RPMs, but there isn't enough evidence one way or the other to know if this is true. There are gazillions of high-boost forced induction motors out there with MSD though.

4) Going from high octane down to lower octanes can cause pinging because the ECU learns to advance spark on the high octane. It should correct pretty quickly though, after detecting a few knock events. I usually reset my ECU any time I have to fill up with 91 or 92 octane, since I normally run 93. That's surely overkill though.

5) You may find that 7ish psi with a Roots blower and a stock ECU can't be done on pump gas. It's quite possible that you need more retarded timing than the ECU can do. Further enriching the fuel mixture, or injecting water or alcohol, might help some.

[-K-]

Reset the ECU and see what happens. If it still pings I'd say it's the octane.
Or the high compression.
Or the N/A ECU not pulling enough timing.
But that can be fixed you will just have to decide what to try next. If it was me I'd try the turbo ECU.... Well first I'd get a WB02 to see what the AFR is.

[douglas vincent]

Its gone now, I think the ECU got used to 92 again.

[Brat4by4]

http://www.streetrodstuff.com/Articles/ ... etonation/

Very informative.