Which goes first ?

[matt]

I have acquired a 1st gen Apexi S-AFC . To fit this it has to be connected to the map sensor pin on the ecu.......

 

I already have an HKS FCD fitted, so the question is which in order should i hook these up?

[Guest Martin F]

You need to tap into the real MAP sensor signal, not the modified one going back into the ECU.

 

So take the signal that comes from the MAP sensor and into the FCD.

 

Sorry don't have colours or pin numbers to hand.

[matt]

Thanks Martin

 

I was wondering if it would make any difference as I presume the signal from the FCD is untouched until after 1bar ie when it defeats fuel cut

[Guest Martin F]

Yep, if you took the one after the FCD you'd only be able to adjust fuelling up to approx 1bar, which i guess is not really much use to you.

[Branners]

Does the fact that Matts car is an import affect any of this?

[Guest Martin F]

Nope...MAP sensor is a MAP sensor.

 

Matt - I have just checked the AFC wiring instructions (on APEXI USA site) and looks like my suggestion to put it pre-FCD may not be the best.

 

I thought the AFC took the MAP signal and then used this to modify the pulse width going to the injectors directly. It doesn't it modify's the MAP signal and then relys on the ECU increasing fuelling due to a modified MAP signal.

 

Apologies for the confusion, but the best solution will depend on what your FCD actually does, i.e. what type you have.

 

I will edit my original post in a while.

[matt]

Yeah I figured it would depend on the FCD .

Apologies for not being clearer earlier , but I was using an onscreen keyboard and stylus on a 5'' screen..... I couldn't be arsed writing anymore.

 

Anyhoo , what's the correct way to wire this bearing in mind i have the HKS FCD which I believe scales the signal rather than clamping it?

 

I've just fitted the SAFC before the FCD ..... ie MAP signal flows through S-AFC then thro' FCD then to ECU

I can't see anything wrong with this upto 1 bar. I presume the signal will be scaled from 1bar upwards as it has been without the S-AFC?

[Guest Martin F]

If the HKS FCD is a scalar unit (which i also think it is) then you will be fine as long as you take into account that whatever percentage you add to the signal is going to be knocked back down again by the HKS FCD.

 

i.e.

MAP Sensor Signal = 1v

AFC Modifies +15% = 1.15v

HKS FCD Scales down 10% = 1.035v

 

So therefore overall your signal has been increased by only 4% and this will result in only a minor change in the fuelling rather than a 15% (or there abouts) that you may have expected.

 

So your settings on the AFC would be totally different to somebody who is using a clamping FCD.

 

You could have fitted the AFC after the FCD and your settings may have been simpler, but you run the risk of hitting fuel cut as your FCD signal would be being increased. Sort of defeats the object.

 

Does that make sense ? Be good to get confirmation from PB.

[THOR Racing]

Martin is correct (in my opinion).

 

Although I always say a clamping FCD is better than a scalar one for the reason of keeping the low RPM fueling as Toyota intended and not scaled as HKS do, creating problems before you start in my opinion.

 

Note: +15% (as in the example) can only ever help in the LOW rpm range!!! NOT in the high RPM range where you actually need it!

 

This is because the AFC CANNOT increase fueling above that of the fuel system of the car.

 

Many people mistakenly think that the AFC will give more fuel, how can it?? For a start it's limited by the fuel cut threshold!

 

The AFC and similar devices are only any good for adjusting low RPM lean points (i.e. increasing fueling at low RPM points to get over say a lean point between turbo transistion or something)

 

You're not going to be able to get 15% more fuel at wide open throttle, the little injectors are running 100% at 18psi, can't get more than that!

 

The solution of course is to increase the fuel supply by fitting a rising rate fuel pressure regulator, a bigger fuel pump maybe or bigger injectors. Then the AFC can truely CONTROL more fuel than stock.

 

So summary:

AFC on stock fueling = Improving upon lean spots in the low rpm band. No good for high RPM, high boost. Only if you're running too rich and use the AFC to lean it out slightly, but not many times that happens.

 

AFC on modified fueling = more fuel control and hence more boost atainable, also used to lean out the bigger injectors back to stock levels for low RPM range.

 

 

Regards

Pete

[matt]

Thanks Pete

 

I'll be in touch about one of your FCDs as I have never been really happy with the HKS version

I understand the purpose of the AFC and have fitted it as I'm about to fit the bigger 550 injectors and so I can trim down the fuelling at lower revs. I have already fitted an uprated pump..

I also realise that there isn't much that can be done above fuel cut...

 

Another Question you may be able to help with... the Resistor pack on the UK models with low impedance injectors.... is it simply a bunch of 6ohm resistors in a heatsink or am I missing something??