I am a little confused with my ignition timing. I know that, for setting the base ignition timing you have to:
1) warm up the engine to normal operating temperature,
2) jumper the service connector
3) use a timing light and rotate the distributor to set the timing,
4) after done, turn off engine and reconnect the service connector.

I've done this but the results is confusing. For my accord, after I jumper the service connector, I checked my current base timing. It was at 15 degree TDC, which is within specification. After shutting off the engine and reconnecting the service connector, I turned the engine back on. When I checked the timing again, the timing was retarded to 11 degree TDC. Why is it retarded when the operating condition has not changed? It is only idling.
Please help clarify my confusion.

Thanks,
beocop

 

the engine will constantly move the ignition timing after setting the base timing, this is normal

thats why you jumper it while setting the base timing, it prevents the ecu from trying to move it while you set the base timing

 

If the ECU constantly adjust the timing, why is setting the base ignition timing important? It seems like the ECU controls all the ignition timing regardless of what you set it to.

 

ECU bases its timing changes on that the base(mechanical) timing is correct. It has, and only needs, a finite amount of adjustment which can only correct for known(pre-programmed tables) timing demands. ECU has no way of actually 'knowing' where the timing is set, nor can it change it to fix incorrect base timing. There is no need to create timing tables(or devices) to adjust for incorrect base timing, when simply checking and correcting can be done. At idle less(than base mechanical) timing is needed so it retards timing, when the throttle is initially opened it will need to advance timing(more than base) to increase engine speed, then at cruise it will adjust again to maximize economy.