Thread: Timing mark indicator is gone. What now?

Doh! I wonder if the Knock Sensor is retarding the timing and the reason why I'm still getting piss poor MPG's



Good luck either way you go

Sticking something on there probably will render the most accurate results

"Doh! I wonder if the Knock Sensor is retarding the timing and the reason why I'm still getting piss poor MPG's "

The knock sensor would not change your base timing. When you go into the "Set Timing Mode" the ECU does not change the timing or idle speed -- it's whatever the raw mechanical setup provides.

Not sure what to take of that. So that means that the timing that you set manually is not reflected by what the ECU can then change?

Nope -- the base timing setting affects all the timing specifications that the ECU sends to the distributor. The ECU assumes that your base timing is 15*. So if it's really 17*, and the ECU thinks the timing at max load and 6000 RPM should be 30*, the engine will fire at 32* because of the advanced base timing.

I was responding to the suggestion that the knock sensor was retarding timing in a way that would affect the reading of base timing with a timing light. Here is why I do not think that would happen --

Under normal idle conditions, the ECU is constantly messing with the timing and Auxiliary Air Control Valve setting to maintain the factory-spec idle speed. This is why, when you just slap a timing light on an idling SR20 the timing will jump around when you are reading it at the pulley. When you put the engine in "Set Idle/Timing Mode" you are basically telling the ECU "hands off - I want to see what the engine does without your intervention." In this mode, you are reading the true base timing, which is what you should be setting with the timing light. It does not jump around, and it changes as you rotate the distributor. Same for idle -- in base idle mode, when you turn that idle adjust screw, the idle speed changes. If you are not in idle adjust mode, the ECU will work against any changes you make in idle speed or base timing.

So, I don't see how the knock sensor retarding timing at higher loads and RPMs is going to change your base timing, which is measured at idle, with no intervention from the ECU with respect to spark timing.

Thanks for clarifying Bill!