A friend of mine (TypeSH) and I both have '02 S2000's with similar modifications. The only real difference between them is that I have a V-AFC, and he does not. He got one of those Techtom OBD-II devices for Christmas, so we hooked it up to my car and went for a drive. During the drive, we noticed that my ECU is advancing my timing by around 10% more than his throughout my VTEC range.

The only reason we could come up with is that the ECU thinks there is less air (due to the V-AFC), so it is allowing more advanced timing. Does this sound right?

 

On second thought, we also have different spark plugs. My plugs are 1 step colder than his. Could that be the reason?

 

On the other hand, the VAFC should have no direct effect on your ignition timing. Were you also monitoring temps? If not, too bad. Insufficient data to reach a conclusion. Try capturing coolant, intake air temp, and ambient temperatures and then make your comparisons.

Why would a lower manifold pressure prompt the ECU to advance ignition timing?
What would a VAFC have to do with MAP readings if its properly installed?
How would running richer or leaner modify your MAP sensor readings?



Plugs may be a "factor" in a fringe sort of way. Without temp captures no dice, and no final answer.

 

We were monitoring coolant and intake air temps. My coolant hovered around 175 deg. F, and my IAT fluctuated between around 85-125 deg. F (it changes VERY quickly depending on throttle position). These were not much different than what TypeSH experienced.

The V-AFC adjusts air / fuel ratio by changing the signal from the MAP sensor. If it is trying to lean the mixture by 2%, it alters the signal by some amount (I'm guessing by about 2%).

I'm guessing that the ECU may be allowing more timing advance, since less air (and fuel) may have more tolerance for detonation. I'm just guessing that this is the case, since detonation is such a problem with FI.

 

I"m pretty sure ignition timing follows a map with RPM and MAP as input just like the fuel map. If thats indeed the case then yes changing your MAP reading via a VAFC will have an effect on timing via the ignition map. Take a look at the AEM EMS software sometime, its very informative as to how an ECU such as ours operates.