So...i learned in my automotive technology class WOT it doesnt really monitor the fuel thats going into the engine , it closes off vacuum and just dumps fuel in at full injector/fp capacity.
Is this true with rotaries/RX7's as well? and if this is true, how are you supposed to tune the SAFC or whatever for WOT when the car doesnt give a **** either way and lets the fuel flow at full injector capacity?

This is another question, but not as important as the first: Can you tune the SAFC2 for both low throttle and high throttle, or does it matter.

 

I don't see how that is true or how it could work.

 

uhh....maybe you should look for another teacher

 

Get him to name a car that runs like that. Its total bullshit.

 

Maybe I misunderstood or something, cuz the guy is pretty knowledgable.
So is there a difference in WoT vs not WoT as far as AFR's go? And do people usually tune the SAFC for WoT?

 

That's a very rough description of what is happening.


It is to a point.
Once the ECU knows you're at heavy load (i.e. WOT), it reverts to a fuel map.
This fuel map uses the air flow meter is it's primary load sensor.
So, the ECU knows how fast the engine is spinning (i.e. RPM's via the CAS) and how much air it's ingesting (the AFM), it goes through a look-up table (i.e. the fuel map) to calculate the proper fuel injection duration.

See above - the S-AFC adjusts the AFM signal.
The AFM is the primary load sensor for the FC3S.

I don't think the low throttle is as important at the high throttle settings.
I would concentrate on the high throttle stuff first.


-Ted

 

Thanks Ted, you can really spell it out. The people that hate on you are full of ****.

 

 

Your instructor is talking about closed-loop vs. open loop. Yes, at WOT the ECU ignores the O2 sensor input on all vehicles that I know of. This is because the O2 sensor does not react fast enough to allow accurate fuel metering through the ECU under dynamic conditions. The O2 sensor input is used by the ECU only in steady-state conditions like cruise or idle.

The fuel dump is usually called acceleration enrichment, which is just a way for the ECU to fudge the amount of extra fuel needed under acceleration. I don't know of any systems that dump the fuel at the full rate, but I guess you could look at it that way to simplify the process. Anyway, this enrichment is added to injector pulse width specified in the ECU base fuel map, as the base fuel map is only set up for static conditions (constant load and constant rpm). The faster the acceleration, the more enrichment is added to the base map injector pulse width value.

The throttle position sensor (TPS) is usually used to determine the acceleration value, so this is usually what controls the acceleration enrichment. If the TPS is not very accurate (S4 RX-7), and more like an on/off switch, then the ECU will not be able to have a very refined acceleration enrichment function. If the TPS sends a more refined signal (S5 RX-7), then the acceleration enrichment can also be more refined. The refined signal allows for better on/off throttle, partial throttle, and gradual throttle changes. The advantage to more accurate acceleration enrichment is that smoothness and power are increased because too rich of a mixture will cause the engine to bog a bit, and a less-accurate acceleration system is usually set a bit on the rich side just to be safe against a possible lean situation.

Well, I don't have any experience with an S-AFC, so I can't comment on that system. I suggest checking in our S-AFC forum for that information.

However, in the case of a generic EMS application, you would first set up a static fuel map (usually on the dyno). Then, you would make acceleration runs to set the acceleration enrichment. The acceleration enrichment is a little more difficult to set, and usually requires a knowledgeable tuner.

 

Thanks evilaviator, nice explanation

 

Yeah... a CARB works that way, going WOT on a carb "closes off" vac and the carb just dumps all the fuel in it can. If you've ever seen a carb without an air cleaner at WOT, you know why the term "dump" fuel is correct.... EFI is just a tad different than that.

On a stock engine, if the car was run WOT and the EFI actually went 100% duty on the injectors, the car would just stall and die and if its a rotary, probably flood itself, heh. I doubt our injectors on a stock rotary see over 70ish% Duty cycle @ WOT... STOCK.

EDIT: well damn... the above post sounds smarter than mine, read it.