NO.


-Ted

 

We got lucky, and we stumbled upon the stock Cosmo (yes, it's not quite an FC3S) ignition timing map as reference.
The last generation Cosmo was made about the same time as the FC3S, and it's engine controls are similar.


The boost sensor is a true "2-bar" MAP.
It can read up to ~15psi of boost.
The ignition maps were mapped at least to 10psi, IIRC.


Ignition timing does advance as RPM increases, but it is also retarded dependent on boost levels.
Look at almost any good ignition map (there are lots all over the forum), and you can see this for yourself.


That's the million dollar question.
I've used an FCD up to 15psi with no problems.
You need to use the best octane fuel you can get your hands on.
Octane suppresses pre-ignition from the advanced ignition timing.


That is the assumption.
Again, good octane fuel should help here.


-Ted

 

thanks for your answers Ted, They are much appriciated.

it helps to know that there actually is no answer and im not wasting my time searching a forum for one.

 

The only effect the MAP sensor has on "fuel injection amount" is the overboost fuel cut. That's what the FSM is referring to.

Actually the info quoted is correct. If you read it again you'll see my comments were about EFI systems in general and not specifically about the FC. This probably would've been clearer in the context of the thread it was copied from. Since posting that (ages ago) I've learnt that the S5 uses the full-range TPS for transient fuelling. Not sure what the S4 does.

 

Geez Ted, I thought you ALWAYS took everybody's feelings into consideration.
OK, I surrender.

As this was posted quite a while ago, and part of his overview on EFI systems, it was taken out of context.

I do have a question though, after 2PSI of boost, as I'm assuming fuel delivery must be altered depending on the boost level, what feeds the ecu to ultimately change the fuel delivery if it's not the boost sensor? If it's just the AFM or TPS, I can run 3/4 throttle at 2 lbs and 3/4 throttle at 10 lbs, so fuel delivery must be changed somehow, unless I'm way off base once again.

 

You don't seem to understand how AFM-based EFI systems work. The ECU takes the airflow and rpm measurements and injects the correct amount of fuel for those conditions. Obviously as boost increases so does airflow, and the ECU reacts accordingly. The ECU doesn't need a MAP measurement to calculate fuel requirements. The relationship between boost and ignition timing is different, hence the MAP sensor's use for this.

 

Jason:
I do understand, but I thought that the increase in airflow isn't proportional to the increase in boost. It seems that MOST everyone on this site as long as I can remember has always indicated that the FCD will trick the computer and create a lean condition at higher than fuel cut boost, but according to the recent information that the MAP doesn't change any fuel map over 2 lbs then we've been wrong for years, or at least I've been wrong for years. Just find it difficult to believe that even Paul Stoaks (FCD write up) would be wrong, but I guess it can happen if testing isn't accurate. I even got hammered for mentioning that larger injectors are needed because of the decrease in fuel mixture, and a possible lean condition at the higher boost levels, but once again if it's the AFM that controls the mixture, this is incorrect.

So am I now to assume, that using a FCD causes no harm whatsoever when boosting to 12/14 lbs, other than a difference in timing, and obviously as has been stated, the AFM will take care of the fuel mixture? This is what Ted indicates, and I assume your thoughts parallel his? If this is true, a lot of guys have been spending money foolishly over the years to create the correct fuel mixture at higher boost levels when the AFM will do the work for them, and then only the timing needs to be addressed.

I guess I need to start looking at some before and after air/fuel maps.

Thanks again

 

Well, after doing some more homework, it seems as though you(Jason), Ted, and a few others have stated for years that the pressure sensor doesn't add any input to the adjustment of the fuel mixture. So I guess that answers the question as to the FCD inhibiting a fuel mixture change, and creating a lean condition. The only lean condition would be when the AFM is calling for more fuel, and the stock injectors are maxed out, leading to a needed upgrade.

I guess it's live and learn time once again.
So, to sum it up, a FCD isn't the villian I once thought, no harm. Now I can take a nap as I'm exhausted from all the research.

 

It isn't, but that doesn't matter. What matters is having the correct AFR, so if the ECU knows how much air is entering the engine (from the AFM), it can calculate how much fuel is need to match it. Boost is irrelevant to that calculation.

The way I see it, this myth has come about because people who assumed the MAP sensor controlled fuel saw engines fitted with FCD's blow because of detonation, and decided it must be caused by a lean mixture. But ignition timing that's too advanced (because of the FCD) will cause the same thing. Making the mixtures richer will lower combustion temps and hence supress detonation, so if you are using a FCD and cranking the boost up, more fuel is necessary.

Not necessarily. The stock EFI system has it limitations, like how much airflow the AFM can measure before maxing out. Fuel controllers that allow you to increase fuelling as revs increase can get around that though.

Even if they were doing it in ignorance, adding fuel does work in preventing engine death, and it's also a lot easier to do. Bigger injectors and fuel controllers are readily available, but remapping the stock FC ECU's ignition timing is almost unheard of beyond the Rtek's very mild tweaking.