JayCar FCD (Fuel Cut Defender,Defeater, Defence) 1jz How To?

[boothy_99]

G'Day Toyo Lovers

Currently looking to touch on some higher boost in my JZX81, Maybe have a play at 16psi see it, then back it back down to a daily setup of around 12-13. However I cant do this with the factory 14.7PSI boost cut and have decided to go down the path of the JayCar DIY kit they have.

Any Help on anyone who has given this a go with their 1J's would be very much appreciated!

(please, no one tell me what it can do to my engine, I'm well aware)

Cheers Guys

Bootyh

[wilbo666]

The Jaycar kit is pretty straight forward

Info on it here:
http://www.siliconchip.com.au/cms/A_108397/article.html

Wiring is as follows:




Also if you want to change the voltage it outputs from 3.9V to something else that is quite easy. FYI and output of 3.9V is equivalent to capping the boost to ~9.5PSI.

See this thread for info to allow you to calculate it...
http://www.toymods.org.au/forums/sho...d.php?p=601658

PSI = (MapOut_mV - 2660mV) / 130.5

Cheers
Wilbo

[rshuwy]

air on the side of caution in regards to tuning, and this clamps the signal, which is the worse of two evil in regards to tricking the ecu.

[e30-323ti]

air on the side of caution in regards to tuning, and this clamps the signal, which is the worse of two evil in regards to tricking the ecu.

For my app. I had planned to have a pressure switch (inline or via relay) to effectively bypass the FCD and enable the factory boost cut if the desired threshold was exceeded.

Still a band-aid solution however.

[boothy_99]

Cheers Wilbo

I'm, a Tad confused. I can see 6 wires on the JayCar FCD, do these other ones simply standalone and not become part of anything, I HATE electronics, they confuse and also annoy me.. However I appreciate them as I have seen their power on many occasion.

Also, If i was to set a cap at say the 17.5PSI At 4.92V, how do I got about modifying the fcd to do that? Unusual that it comes readily set on 9,5PSI as thats lest than the factory fuel cut.

Cheers for helping out a noob

Booth

[big_zop]

No, what it does is clamp the voltage to trick the ECU into thinking it is only running 9.5psi so wont boost cut. The problems the other guys were eluding to was that if you are running 16psi and the ECU thinks its 9.5, then you run the risk of running too lean.

From what I understand, you wont be able to run a higher boost cut limit either for protection. Not unless you have some sort of programmable device or pressure switch set up as e30 mentioned (ie; you would clamp at say 14psi so it wont boost cut but when you go over 17.5, it will behave normally which will activate the standard boost cut).

[wilbo666]

I'm, a Tad confused. I can see 6 wires on the JayCar FCD,

You might need to take a picture for me mate, I can only assume that it doesn't look like the one with 4 wires I showed above?

Hmm does it look like this? If so it the upper two wires on the right don't seem to do anything... the rest of the wires and componenst look like they line up with the image I posted previously ... (also from the silicon chip website)

Also, If i was to set a cap at say the 17.5PSI At 4.92V, how do I got about modifying the fcd to do that? Unusual that it comes readily set on 9,5PSI as thats lest than the factory fuel cut.

You can't set the Jaycar kit so that your boost cut is 17.5psi unfortunately, with the jaycar kit your options are to remove the boost cut or not... if the engine ECU sees anything above its boost cut pressure it will cut.

But it is possible to change the Jaycar circuit to that you can change/set the highest pressure value that the engine ECU sees however (i.e. higher than 9.5psi)...

I.e. You can set it up so it is as follows... (In this example you are clamping at 12psi)
@6psi real -> the engine ECU sees 6psi
@8psi real -> the engine ECU sees 8psi
@10psi real -> the engine ECU sees 10psi
@12psi real -> the engine ECU sees 12psi
@14psi real -> the engine ECU sees 12psi
@16psi real -> the engine ECU sees 12psi

By changing 2 resistors you can set the clamp value.... the two resistors to change are highlighted in the below image.


Using the below table you can work out what value resistors you need for a desired clamp output to the engine ECU. As you can see the default resistors (1000ohms + 680ohms) set it to around 9.5psi.




Cheers
Wilbo

[boothy_99]

So, from my understanding, the best possible solution is to set it at the highest possible pressure the ECU sees, to allow for mixture compensation during higher boost?

Another curiosity, with this constant changing, does the ECU compensate accordingly through the boost increase?

For example the original condition FCD compensates up to 9.5PSI, then after the engine is constantly being run on a fuel mixture of 9.5PSI Boost Reading?

If the FCD is modified to see the highest possible boost, isnt this the the best possible solution?

boothy

[wilbo666]

It really depends, you might find that 9.5psi gives an AFR which is good, but as you say clamping just below boost cut is the most conservative

Also worth thinking that the ignition timing at 9.5psi might be different to that at say 14psi

Cheers
Wilbo

[rshuwy]

So, from my understanding, the best possible solution is to set it at the highest possible pressure the ECU sees, to allow for mixture compensation during higher boost?

Another curiosity, with this constant changing, does the ECU compensate accordingly through the boost increase?

For example the original condition FCD compensates up to 9.5PSI, then after the engine is constantly being run on a fuel mixture of 9.5PSI Boost Reading?

If the FCD is modified to see the highest possible boost, isnt this the the best possible solution?

boothy

ideally you would want the ecu to have an exact reading for the psi, but that isnt really possible for a performance stand point with the factory ecu, its way too rich once boost and rpm come on, check out my graphs for example, (before and after fcd/safc). hence the band aide solutions of the fcd, although ignition timing hasnt been a problem, i dont know what the hell it is doing at those rpms/boost, hence the more you clamp down the map sensor input into ecu, the more likely you could run into some problems, this type of fcd (jay car), clamps the signal at a certain point, the signal will be uninhibited until it reaches that point, then from that point onwards it doesn't go past that point, even tho real pressure does. a fcd of the hks/potentiometer type acts across the whole pressure range, and hence allows more tuning, as you can dial in the output voltage that will be representative of the real pressure at say 16 psi, but still not boost cut, as it doesnt pass that 4.9v mark etc.

[boothy_99]

To help find a pretty right AFM for the boost I will be running I think I might also back it up and buy one of the JayCar AFM Meters which displays it in a numerical display on a small LCD screen. Has anyone had experience with these before?

That can then determine what resistor combo I will run in the end on the FCD to find the perfect AFM for a range of boost.

I guess if it goes up shit creek, I can always simply remove the FCD.

Wilbo, I am also confused about your diagram, Mainly colours? The diagram you posted features a grey and green coloured wire, I cant see those colours on the FCD Picture? or is it simply just a reference? excuse the noobness.

Boothy

[skin]

i ran 14 psi with a jay car FCD, had it dynoed and the AFR were really good, they are quite rich from factory

[wilbo666]

Wilbo, I am also confused about your diagram, Mainly colours? The diagram you posted features a grey and green coloured wire, I cant see those colours on the FCD Picture? or is it simply just a reference? excuse the noobness.

Boothy

I've simply taken my pictures from the Silicon Chip website...

Not sure if that answers your question or not?

Cheers
Wilbo

[orangeute338]

has anyone had any suscess with the jaycar fcd? what value resistors did you use?

[wilbo666]

hey mate, i found a old post about the fcd, i just wondered if you could help me out. i cant seem to get rid of the boost cut.

i have the jaycar fcd and i first tried 680 and 330 resistors but still cut out, then tried 830 and 330 and still cut out and now i have 1k and 330 and its still cutting. if there a magic number to get it close to boost cut? i didnt want to set it at the 9.5psi how it comes standard

its on a 1jz from jzz30

cheers
Josh

Hey Josh, I'm not a fan of PMs, best to get question out in the open so the next guy that has the same issues has a chance of finding the answer too mate!

1kΩ + 330Ω for R1 & R2 (as shown in my above post) should equate to a boost cut clamp of around 11.5psi.
The engine ECU shouldn't be getting boost cut at 11.5psi so I would be testing the Jaycar FCD.

One way to test it all is as follows.
1) Get a small plastic syringe from a chemist
2) Unplug the hose from the intake that goes to the MAP sensor and connect the syringe to it.
3) Turn the ignition on
4) Get a friend to press on the syringe to apply pressure to the MAP sensor and at the same time measure the voltage that comes from the MAP sensor as the input to the Jaycar FCD with a multimeter. The voltage should be ~2.67V when open to normal air pressure and the voltage should go up as the syringe is used to exert more pressure to the MAP sensor
5) Do test 4) again but this time measure the 'output' MAP voltage from the Jaycar FCD. It should be the same as the input MAP voltage up to ~4.2V and then stay at ~4.2V even when you apply more pressure via the syringe (if you have 1kΩ + 330Ω fitted and the circuit is working correctly)).

Does this make sense?

Cheers
Wilbo