How a FCD works...

[Glanza_cl]

Doesn't seem to be much info out there to new member about FCD's (Fuel Cut Defenders) and how they work... other then options like there baaad or yeah there fine lol.

so here is a quick run down and explanation about them:

The basic function of a Fuel Cut Defender is to alter the signal to the ECU and allow you to run a greater boost level, how does it do this?....

Well the ECU takes readings from the MAP sensor (manifold absolute pressure sensor) which provides it with an accurate table to fuel the car through the rev range. Different air levels and air density will alter the voltage readings the MAP sensor produces which then in tern tell the ecu to alter the fueling to accommodate.

A FCD sits in the line from the MAP sensor and ecu creating another point for the voltage to pass through. It works by monitoring the signal, (voltage), sent by the MAP sensor. As a rough guide, 1 bar of boost equates to roughly 4.5/5 volts, so the FCD will receive these signals and let them pass through to the ECU until it reaches a certain voltage level e.g. 4.1volts or around 0.8bar. The FCD will then clamp and hold this voltage so the ecu 'thinks' your still at 0.8bar but in fact you have surpassed this and increased the boost level to say 1bar with MAP readings of 5volts or more.

Now this isn't necessarily a bad thing, you have upped the boost and have more power and torque... happy days BUT! your ecu still thinks your only boosting 0.8bar how is it going to fuel your engine for 1bar or more?... it isn't! so what do you do now?

RRFPR-

this will increase the fuel pressure allowing a greater volume to be used through the range (making you run allot richer then before) getting rid of any 'lean' spots that had been created top end, but now you have another problem you are running rich across the WHOLE rev range making idle and cruise equally as rich as the top end of the rev range . This is where simple fuel adjusters come into play like the SAFC and APexi Neo etc.

Apexi SAFC and other fuel controllers-

These allow you to alter the fueling across the rev range in increments i wont go into detail as a quick google will throw up allot more then i can explain here

Basically if you want a SAFE set up you must realise that the FCD will lean off the fueling as its tricking the ecu so a RRFPR would be needed to compensate, a trip to a RR (rolling road) is a MUST!) so the RRFPR can be set up to fuel the correct amount. Over rich and you could get bore wash where to much fuel is pumper into the chambers and not burn in combustion creating allot of problems. Not enough fuel and your Lean and will be creating allot of heat build up... this will make your engine go bang in some form or another.

FCD's arnt all bad, used and set up correctly you can get good gains and results. the horror stories come from people that with out the correct knowlage have slapped one on, upped the boost to 1bar or more then run the engine lean and blown it!

Hope that helps some of you get your head around it and if you have any more info that could help feel free to add it

[Starbuck]

good info

[BigMan]

learn something new everyday thanks for the info

[LukeH]

good write up, verry clear.

[N80Jamie]

Already had some basic info off you about this before. This explains everything very well! Great write up

[BearFaceOfDoom]

So for example I want to up my boost safely to produce around 160bhp.

I have mani, decat, catback exhaust, blitz s/s induction kit. I have also got to up the boost. HKS adjustable actuator, HKS FCD and GReddy Profec B manual boost controller.

So to up the boost safely I still need a fuel pressure regulator, uprated fuel pump and a fuel management system? Am I right? Anything I've missed?

[Russleh]

^^ sounds about right.

some good info there. i wasnt quite sure about all this safc stuff before or what the fcd actually did. do now tho

[Glanza_cl]

At a minimum just a RRFPR will do, but something like a SAFC will give greater fine adjustments. an uprated fuel pump is always good as the stock item might be the original from when it was first put in (so like 14years old lol)

sounds like you got the rest sorted, but 160 you shouldnt need one... i made 170 on the stock ecu

also glad the information is helpful

[Steve GT]

brilliant write up thanks for the info mate its a lot clearer now

still dont like the bloody things though lol

[Lukew360]

Great write up, really clear information on the first read through.

This should be stamped!

[Russleh]

x2

[Steve GT]

Great write up, really clear information on the first read through.

This should be stamped!

my thoughts exactly

[Glanza_cl]

Ah cool, its nothing special but there doesn't seem to be a thread that explains what a FCD does, how it does it, and what mods make it worth while and safe

[TrisK]

does fuel cut always bring the engine light on?

or can it just miss until you back off ?

[Glanza_cl]

When boosting the engine check light will come on as a sign your about to hit fuel cut (like a last resort preventative), not that you have hit fuel cut. But people tend to hit fuel cut so quickly it pops up and they assume its because they hit fuel cut.

There where times i boosted and the check light came on but i didnt hit fuel cut, but it would have been right on the voltage thresh hold. This normally would happen in the higher gears where your building greater boost levels from being on throttle for allot longer. (hence why you should set up actuators and EBC's in 3/4th or 5th gear)

I cant remember 100% but i don't think there was ever a time that once i had hit fuel cut the engine light didn't come on.

[Gainzy]

I have a superchips fuel cut defender out my glanza, £55 posted if anyone needs one

[russ78]

How do you test a fuel cut defender is working properly before fitting it to a car ?

[Starlet-Matt]

I've asked my local tuning garage if they could fit my FCD to my starlet gt,

And he's asking for a ecu diagram/ecu pinout?

And a wiring diagram for the FCD :/

[CaroleBaskin91]

Great info this! Cheers mate

[Sam44]

Yeh nice info. The hks fcd is adjustable this does a slightly different job not just clamping the upper voltage but able to in multiple stages reduce the map sensor voltage out put so as to not hit the higher voltage fuel cut comes in at.