Mikeymx5

iTrader: (2)

I had a question about the Timing on a NB

Background:
I started by using the Xede which only controls timing on the crank. The New AEM FIC Controls both timing on the Crank and on the CAM . The result is lower HP numbers for the FIC.

I know that on my old NA I would adjust the sensor on the CAM to advance or retard timing but on the NB this was no longer possible.

Can anyone give me an explanation of how the ECU uses these signals?

My though is to disconnect CAM sensor from the FIC and force the FIC to only control timing on the Crank like the Xede does.

Joe Perez

iTrader: (8)

The crank signal is what triggers the ECU to start the firing countdown. IOW, it's the one directly responsible for timing.

The cam signal is not critical to spark advance. It's just there so that the ECU can tell the difference between TDC and BTC on the crank. You can alter the cam timing (with adjustable gears or VVT) without affecting spark advance at all.

On early Miatas, the CAS outputted two signals, one of which was the equivalent of the crank signal on the NB. So twisting the CAS was effectively like moving the crank sensor on the later cars.

Mikeymx5

iTrader: (2)

That helps alot, I was wondering what changed in the setups NA to NB.

SO I wonder why advancing both will cause lower HP numbers.

Joe Perez

iTrader: (8)

From an electronic standpoint, damn near everything. To a mechanic or a suspension guru, the NA and NB are pretty much the same car. To a EE however, they might as well not even be made by the same company.

Delaying or advancing the CMP signal on an NB (within the limitation that you must not cross a CKP pulse) will have absolutely zero impact on ignition advance or horsepower. Anyone who says otherwise is wrong / misinformed / an idiot*.


(*) On an '01 or later, altering CMP independent of CKP (or altering CKP independent of CMP) will **** up the VVT system's cam angle calculation, and probably cause a loss of power due to improper cam timing.

Mikeymx5

iTrader: (2)

OK I need a dictionary to understand what CMP and CKP spell out, but anyway, I have been tuning out the FIC and I am still under the HP numbers that I was making with the Xede. Not sure why? Both AFR and Timing are right on target.

Some people mentioned that advancing both the cam and the crank together makes a difference.

The Xede as I stated only advanced the Crank timing and worked well as long as you dont pass about 10 degrees. Which I suspect is what you were talking about crossing the crank and cam timing signals.

Im really just trying to understand how the system works, so I can make a better educated decision about how to proceed.

I looked in to all possibilities why this would be and I dont have alot of explanation, but it could be something as simple as changing the injector delay time, causing less ionization. This could reduce the HP with out changing the AFR. Or I could be way off?

Joe Perez

iTrader: (8)

CKP = CranKshaft Position.
CMP = CaMshaft Position.

These are the names commonly used to refer to those two particular signals. The FSM also uses the terms G (for CMP) and Ne (for CKP), though these terms are not as commonly used in casual conversation, as they are somewhat less intuative.


Different day of month, different phase of moon, etc. How big a discrep are we talking abuot here?


You mean atomization?

Changing injector constants will change AFR. It doesn't really matter what portion of the injector's cycle time the ECU thinks is lag vs. actual delivery- the physical characteristics of the injector don't change.

Mikeymx5

iTrader: (2)

You are correct, thank you.