FCD's?

[Guest Usmann A]

With devices such as FCD's, where does the stock fuel cut system take its readings from, I assume from the fuel pressure regualtor and some type of turbo boost sensor, by a volatge signal to the ecu.

So, fcds bascially drop this volatge signal, if it bases its activation on the FPR then surely it is reciving a incorrect signal( showing that the FP is lower than reality), and many people say this makes it run lean.(incorrect afr, ecu is supplying less Fuel accoring to the air at that moment)

Although ,I thought the ECU bases its fueling mainly upon the MAP reading(hence afc contorller), if the MAP reading is un-tampered with how can the ecu make a judgement.

As it is seeing a fake fuel pressure reading(by voltage), but on the other hand it is seeing the correct Pressure of intake air(which is what MAP is I hope), and then it trys to match the correct amount of fuel with air, thus allowing fuel cut to be activated again.(not getting rid off it?)

I am not getting this, unless Fuel cut is also evoked from the MAP sensor supply also??

Or seeing as their is a certain boost limit, it must take a signal from a boost sensor, it shouldnt need to, as it probably knows how much fuel will be used when running over 14psi(its fuel cut limit)?

Or the fact that FCD's adjust more than one signal inputs to the ecu?

(do the HKS FCD, and the BCC work similar?)

 

HOW DO THESE DEVICES WORK??

I would like an indepth explanation please,

 

 

 

 

 

 

 

Rgds

U

[Ian C]

First off, it's all done on the manifold pressure. Fuel pressure isn't measured anywhere by the car, it's built mechanically into the regulator.

 

If the ECU sees a high MAP reading, it initiates fuel cut. Pete Bett's defender simply holds the MAP signal to about 0.05v below that threshold.

 

As this is at the limit of the stock MAP sensor's sensitivity and the stock ECU fuel map anyway, it doesn't matter that the signal is clamped. You just need to make sure you are providing enough fuel over and above that amount of airflow.

 

I'm not 100% about this explanation, that's just how I think it works. Anyone else care to chip in?

 

-Ian

[Guest Usmann A]

ok, so Fuel cut is measured on the basis of manifold pressure, so in other words the FCD's reduce the voltage of the signal from the MAP at that certain point to the ecu, therefore the ecu, is thinking that the manifold pressure is still safe.

Andwhile this is happening the FPR is mechanically supplying the fuel, but surely the ecu must have some control over the fpr?

Or does it simply control the pump etc, through the fuel pump ecu?

Evenso, by us advanceing over the fuel cuts limits we are stepping the boundary of the stock map, then surely that is not good?

You say stock map,based the MAP flow? Then how can we run big boost, hybrids etc, and expect the ecu to cope?

Afc, I thought this just adjusts the MAP signal to the ecu, but if the ecu is not mapped to see such high MAP pressures, then how does the AFC conqer this?

Unless, it too causes the ecu to see lower MAP signals, but then then this would surely affect the fueling no?

 

 

Sorry, I know boring for you all, but im interested!

 

 

Cheers for the advice Ian...

 

Is my thinking right, or am I just confising myself even more?

 

 

Rgds

U

[Wez]

Hiya,

 

I think you are on the right lines here, basically the MAP signal is clamped as Ian said so the ECU never sees the higher voltage the problem as you are pointing out is that the ECU will be supplying fuel for what it thinks the MAP is which is not real MAP.

 

The safety is that the FPR which is purely mechanical as Ian also stated has MAP pressure applied which increases the fuel pressure at the rail so more fuel as added.

 

I agree this is not 100% accurate and when people add uprated fuel pumps and FPR`s to go with higher than stock boost you are just increases fuel pressure to dump more fuel in, the ECU would still be at the load site for what ever the FCD clamped the voltage too.

 

It does work as many many cars not just Supras use this method for increasing power.

 

[Adam W]

The ECU doesn't control the FPR or the pump, fuel metering is done by altering injector pulsewidth. Flow through the injectors is proportional to the pressure difference between the fuel rail supplying them and the manifold pressure they are trying to spray into. Hence, the FPR is referenced to boost pressure so that the pressure differential across the injectors remains constant.

 

Going over the stock fuel cut limit is where your fuel mapping will begin to get a bit vague. There are ways of bodging it but if you want to run serious amounts of air and fuel through your engine the stock ECU will be way out of its depth no matter what you try and trick it into thinking. Your options at this point are full replacement ECU, or the Greddy E-manage (maybe the Apexi FC as well?) which can add injector pulsewidth directly.

 

You're in that horrible no-mans-land where you can make the stock ECU work, but life becomes much easier and tuning much more straightforward if you can ditch fuel cut etc and take full control of what the engine is doing (ie new ECU). All depends what you want from the car and how much you want to spend etc, I got so pissed off with constantly fighting my stock ECU that I ordered the AEM.

[Ian C]

If you put in hybrids, you put in bigger fuel injectors to fuel them, but you trim the airflow signal down with a fuel controller so that the ECU uses a lower injector duty cycle. As they are bigger injectors, you get the same amount of fuel injected for less duty cycle, so this setup works. The drawback is that you need to set up the fuelling so that when the ECU is seeing it's maximum boost pressure (say 1.2bar) the engine is fuelling for your chosen maximum boost pressure (say 1.5bar), which means you will deliver the same amount of fuel at 1.5 bar as at 1.4, 1.3, and 1.2bar because as far as the ECU is concerned, it's all 1.2bar.

 

So it's not a perfect solution, but it works.

 

-Ian

[Wez]

If I am reading the posts correctly it would appear we are all saying the same thing but in our own way.

 

[Guest Usmann A]

Great, now thats cleared it up for me?

Now with having an understnading of this, must say that a AM ecu, would be the best choice, financially your total for all the add on goodies would be not so far off the price of the ecu itself.

 

Cheers guys, I get it now!

 

Oh, last thing, what about the ecu's timing adjust, I thought that it could adjust its ignition timing accordingly, ie, knock sensor at the crank, senses "knock" it would retard the timing no??

If, not then what safety precautions would it take?

 

If it does retard the timing, then would this affect the AFR ratio, I would think not, if "knocking" as we know, causes a slight drop in manifold pressure than surely the FPR would sense this a still fuel correctly?(I understand its diaphgram type constrction is how this meters the fuel?)

 

 

 

Rgds

U

[Wez]

Hiya,

 

The AEM has very good knock control built in but it has to be setup properly, it can pull ign and or add fuel and this can be done across the whole engine or per cylinder, does need to setup properly though which takes a little while, I am still using basic knock control at the moment and will fine tune it when my single is on.

 

[THOR Racing]

I think you've sorted the FCD issue?

Basically it's a simple get out of jail card that allows 80% of would be "modders" to get the power they want for the right price.

 

It is in NO way harmful so long as you get the fueling checked out at the boost you run.

This is because the Jap cars tend to overfuel anyway and we're just using that extra safety margin.

 

You might cringe at that but that's life, you don't get something for nothing.

 

Oh, last thing, what about the ecu's timing adjust, I thought that it could adjust its ignition timing accordingly, ie, knock sensor at the crank, senses "knock" it would retard the timing no??

 

The stock ECU does retard ignition if it detects knock. Gradually advancing the ignition back to stock setting over a period of time (a time of NO detected knocks)

 

 

 

If it does retard the timing, then would this affect the AFR ratio. I would think not,

 

You are correct.

You can treat fueling and ignition as seperate and not dependant on one another for most cases.

 

 

if "knocking" as we know, causes a slight drop in manifold pressure than surely the FPR would sense this a still fuel correctly?(I understand its diaphgram type constrction is how this meters the fuel?)

 

I think you're over analysing this.

 

The knock happens after the fuel delivery so what if it causes a drop in manifold pressure. That only serves to reduce the chance of knock happening again. O.K. the FPR would reduce fuel but it's a mechanical device and would probably not operate that fast. Not fast enough to notice one knock in a rotation of the crank.

 

The retardation in ignition would have more of an effect.

 

In the extreme case where there is a lot of knock then yes, it'll pretty much self destruct. But you've been a bit of a tw&t if you let it get that far.

 

 

All these increases in fuel pump flow rate, increased fuel pressure, front mounted intercoolers, bigger injectors etc etc are just a whole line of things in the process of making your timebomb a little safer. The more you want to push the boundaries of the stock car and it's mechanicals the more you have to help it.

 

Where has all this come from?

Seems someone has suddenly paniced you into buying a new ECU?

 

Ask yourself this.......

 

"WHAT DO I WANT FROM MY CAR?"

 

Then find the best cost effective answer to your question.

 

I agree that with a replacement ECU you have a lot more choices but it costs a lot more in terms of time and setup to get there, and you really need to see a return for your money.

 

Regards

Pete

[Guest Usmann A]

Hi pete,

thanks for the info, no one has paniced me, I was just bored one day and started thinking, thanks to a few old threads in the tech section.

Just causal curiosity, as I didnt really understand this before, but now im a bit better, thanks guys!

 

 

 

Rgds

U