Tech

How is this possible? I've seen a few times in my latest log.

Jason Dove

I've seen that a couple times also, but when it happens to me it's -.1 to -.2 degree's so I haven't worried about it.

Tech

Mine is more significant. TTT

Jason Dove

You could be tossing the Low Octane retard, but I don't know how that gets triggered... I doubt there's an Octane sensor in the fuel tank.

JSK333

I replied to your other thread too.

Do a search in this forum for "burst knock."

Tech

Burst and low octane knock have been disabled.

DOOM Master

I might have your answer. Your knock sensor is probably almost dead. The same thing was happening to mine and it just died on Friday. Watch for your SES light to start flashing on and off and see if you can feel when the knock retard starts kicking in. The only good thing is that the knock sensor is only like $35 from a place like Autozone or Parts America. You can drive without it working, but the car will run like garbage. Mine is right now because I don't have the time to fix it until Saturday.

SABLT194

I think your in Low Octane mode. I've got the same problem. It seems that if you get enough knock counts in a certain period of time, the PCM will start to pull timing based on MAP & RPM conditions weather your knock counter is banging or not. I have this happen all the time on my car and it can be quite a bit of retard. After a while of normal driving with no more knock counts, the mysterious auto retard feature goes away. I've just decided to run good gas (GT 100) at the track and set KR to 0 then switch my program back to normal for street driving and 94 octane gas.

Now my disclaimer:
I can't guarentee that statements are 100% correct because I haven't truely hacked the low octane portion of the code to see how it really works. These are just my observations and some experience with some older GM logic

Steve

96zvert

I read on another post that if it goes into low octane mode, it will only come out when the gas tank level is increased by about 20%, like you filled up with new gas. Does anyone know how to disable low octane mode, or is it possible? My car is doing the same thing.

SABLT194

I don't think that fuel level is an input to the PCM so there's no way for it to know that you've added 20% more fuel.

Tech

I was unaware until recently that there was such a thing as "low octane mode." They car has never had under 93 octane in it.

Tech

Anybody want to see my Tunercat and DM files?

Tech

Nobody knows?

SABLT194

In LT1 Edit I just set my Lo Octane Retard down to 0 degrees and now mysterious KR is gone. Check out the Lo Octane post on www.thirdgen.org in the DIY Prom forum. There's a good explaination in there on how the some of the older Lo Octane code worked. GM probably used much of the same logic on our PCMs as well.