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Originally Posted by EcoCivic
That is very helpful, thank you for the information! I presume that the D series engines uses fixed timing tables too then. Another question- Since the timing tables are fixed, there would be no benefit whatsoever to using a higher octane fuel than recommended since the ECU won’t advance the timing anymore anyways. Is that correct? Also, under normal conditions, would there ever be any knock for the sensor to pick up to retard the timing.
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No reason for higher octane fuel under normal conditions, no, since the ECU will only ever subtract (retard) timing, and never advance it.
Knock sensors are good to have especially on higher performance engines because they allow the manufacturer or tuner to tune advance at higher throttle much closer to the point of knock, since 1) you can't typically advance ignition enough on pump gas to get maximum economy and power at WOT, 2) under these conditions, knock can be very damaging to the engine, and 3) engine knock can vary based on conditions.
Just as an example, the TSX motor in my car calls for 91 octane. It has tables for ignition advance at 6 different cam angles which it interpolates, as well as tables which add or subtract timing from those other tables based on coolant temperature, intake air temperature, and other factors. But, they can't make a table for everything. What if the intake air sensor goes bad? Or, I get a bad batch of fuel? A knock sensor both allows them to be less conservative in their ignition tables and provides protection in case anything goes wrong.
Quote:
Originally Posted by EcoCivic
Also, does the IAT affect the ignition timing? If it does, I presume maybe I could get a little more power by installing a resistor in the IAT wiring harness so the ECU thinks the air is colder than it is and advances the timing more if I use high octane fuel?
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It does, and what you suggest might work, but chances are good that part throttle ignition timing is already very close to perfect and more advance is not necessarily a good thing. Cooler air is more dense, and a higher density charge burns more quickly, so at part throttle it may actually pull timing for cold air, and it might add or subtract at WOT (or have tables for both) depending on whether the faster burn or higher cylinder pressures are more relevant.
I'll take a look at the factors I can modify on my Hondata ECU and get back to you.