Timing off by 11 degrees? How is it possible?

[zer0c123]

1993 240sx Manual KA24DE
What can cause the ignition timing to be off by 11 degrees without touching the distributor? A smog tech measured my timing to be 9 BTDC. Also another mechanic that I know confirmed that the timing was at 9.

3 days before, the smog tech measured it be 20 BTDC, but I never touched the distributor. I had the bolts on the distributor marked when I did a timing chain job years ago, so it never moved from that position.

SO this makes no sense to me. Need some input, because my car does not run right after I had the timing readjusted to 23 BTDC.

Here is how the distributor looks now for 23 BTDC. The black mark indicates where the middle of that bolt was originally for 20 BTDC.


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[zer0c123]

The only code that pops up from Mode II is code 34 for knock sensor.

[asoomal]

I think the knock sensor is retarding the timing...

[zer0c123]

Yea it does look like it....

I've been searching though old posts by Nistech and found this a minute ago.

"If a knock sensor goes open circuit [your failure] It will go into a fail safe timing setting. Meaning it will not allow the timing to advance on accel as much as it would when the sensor is functioning properly"

This might explain why the tech commented that he noticed fluctuating ignition timing with the timing light. I think I need to read more in this. I really don't want to change the knock sensor. It's expensive and I hear it's a PITA to change.

This is starting to make more sense the more I think about what I did before the smog test. Using Arco 87 octane probably sent my knock sensor into over drive mode and code 34 for knock sensor was present during the test. Therefore it probably retarded my timing to compensate for the lower octane fuel. I normally use Chevron 91 supreme, but I was running 2 gallons of alcohol in a 1/4 tank of gas. I didn't want to dilute the alcohol with good gasoline, so filled up on Arco 87.