High or Low Octane Table which one or both!!
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Oz Director
Joined: Nov 2001
Posts: 208
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From: Australia
High or Low Octane Table which one or both!! When does the PCM switch between tables, need the main point or 's??
Is it a combination of thing's or just eg: the IAT vs Temp, that make it drop into the low octane table.
I need to know what the best way to prevent the PCM thinking i need to reduce the timing so it jump into the lower table because of these factor's.
I solve this by mirror image of both tables, but i have solve this, by lower the intake temperature, this can be achieved by plumbing the car intake to pick up cooler air, as i'm talking about the Holden Commodore here. Alot hard to do on our car because the engine is forward and less room for a front entry of intake air.
By doing this i can see the car is still between the high and low tables, compare by mirror image both table the same, which kept it in the high table, there got to be something else that help the PCM to shift into the lower octane table?, i can eliminate Fuel as i am running higher octane fuel all the time.
Would the temperature of the engine play a part in this shifting of the timing into the lower octane table?.
Can there be more than just a couple of parameter built into the PCM that shift the timing via the low octane table, i know Knock Retard play a major part it lowering the timing, but i use high grade fuel, there is no KR recorded on my car!!!.
what do you think can there be something else.
Is it a combination of thing's or just eg: the IAT vs Temp, that make it drop into the low octane table.
I need to know what the best way to prevent the PCM thinking i need to reduce the timing so it jump into the lower table because of these factor's.
I solve this by mirror image of both tables, but i have solve this, by lower the intake temperature, this can be achieved by plumbing the car intake to pick up cooler air, as i'm talking about the Holden Commodore here. Alot hard to do on our car because the engine is forward and less room for a front entry of intake air.
By doing this i can see the car is still between the high and low tables, compare by mirror image both table the same, which kept it in the high table, there got to be something else that help the PCM to shift into the lower octane table?, i can eliminate Fuel as i am running higher octane fuel all the time.
Would the temperature of the engine play a part in this shifting of the timing into the lower octane table?.
Can there be more than just a couple of parameter built into the PCM that shift the timing via the low octane table, i know Knock Retard play a major part it lowering the timing, but i use high grade fuel, there is no KR recorded on my car!!!.
what do you think can there be something else.
Re: High or Low Octane Table which one or both!! I am not very familiar with the Commodore version....but I am going to assume all engine management is the same as the Americana LS1's.
You may be mis-interpreting the IAT timing reduction as the Low Octane Ignition Advance. If you have NO knock retard, then odds are you are still referencing the High octane table. What you are seeing is the actual ignition advance after the IAT makes it's adjustments because of increased air temperature.
You mentioned that you solved this problem by cold air induction. This would also point to the IAT. Underhood temperatures rise significantly as the car is running at standstill or low speeds. A tyipcal air induction, pulling air from under the hood, will suck in this hot air. The IAT sees the abnormaly hot air and reduces timing accordingly.
To fix this problem you will need to unplug your IAT sensor and place a resistor into the plug. I believe a 4.5 kohm resistor will do the trick, but you may want to check on this. This will trick the computer is to seeing a constant cool temperature and will not retard timing accordingly.
Good Luck,
Kevin
You may be mis-interpreting the IAT timing reduction as the Low Octane Ignition Advance. If you have NO knock retard, then odds are you are still referencing the High octane table. What you are seeing is the actual ignition advance after the IAT makes it's adjustments because of increased air temperature.
You mentioned that you solved this problem by cold air induction. This would also point to the IAT. Underhood temperatures rise significantly as the car is running at standstill or low speeds. A tyipcal air induction, pulling air from under the hood, will suck in this hot air. The IAT sees the abnormaly hot air and reduces timing accordingly.
To fix this problem you will need to unplug your IAT sensor and place a resistor into the plug. I believe a 4.5 kohm resistor will do the trick, but you may want to check on this. This will trick the computer is to seeing a constant cool temperature and will not retard timing accordingly.
Good Luck,
Kevin
