2jz fuel cut defender

[triptek]

I need to put a fcd in my soarer, so i was going to use the one below. I'v done some searching and can't find any write up's or decent information on how to put one together.

Any info or pictures would be appreciated.

[The Real Roadrunner]

id personally buy a reputable adjustable one where you can lift the cut but not remove it totally, that way if you want it to run 18psi you can but you can set it to cut at 19psi to avoid a broken engine.

Know what i mean? $5 parts can on alot of occasions cause $5K rebuilds.

Cheers
Linden

[wilbo666]

The problem is the maximum value that the map sensor can read is ~17.5psi.

The circuit that has been posted can still be setup to allow boost cut I'm pretty sure, it just flattens off the top of the voltage vs pressure curve...you you adjust it via the pot

But the highest that you can set boost cut to with the stock map sensor is ~17.5psi (the stock MAP sensor just can't read above that!).

So unless you get another MAP sensor and setup a box of tricks to scale / convert the higher reading MAP sensor to what the engine ECU expects from the factory MAP sensor there isn't a whole lot of options other than just removing boost cut...(On factory management of course! )

Cheers
Wilbo

[triptek]

Anyone got some pics of the above fcd installed. Any help on how it goes together would be appreciated.

[Mos]

The above FCD is a pot and two diodes. If you google potentiometer and diode, you should be able to find images and details of what they look like and how they work. The circuit is so basic that unless someone specifically decided to write up a how-to on this specific circuit it's unlikely you'd find pics of this fcd....
Most reputable electronics shops will tell you which end of the component is which on the diagram and from that you can connect the bits the way the picture tells you.

[Officer Doofy]

This one is better as it allows you to set a voltage to clamp at, allowing you to set the voltage just before boost cut maximising fuel and ing for high boost.

http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm


Oh and i have one of those craptacular fcd in the first post somewhere if you want it. I take no responsibility for any outcomes but.

[wilbo666]

Officer Doofy: 'Better' is a bit of a subjective term , and Craptacular is also interesting...it's simple but does work...please elaborate if you would

If you are happy for the gradient of the curve to be modified very slightly, then I think it is an excellent circuit... it has passive components only so is likely to be very robust, has very few components, requires no power, is easy and cheap to construct, can easily be setup on a plug to be removed if required quickly and it is simple

I went and spent 2mins to simulate the 'Craptacular' circuit for others so they can make an informed decision

Personally, I would also recommend trying to get hold of a WB02 sensor to check that the AFRs are OK, WBO2's are quite affordable in this day and age and offer some peace of mind.

I'd also only use 1 diode, but I thought I'd keep it simpler and just simulate the circuit everyone has

Oh and I simulated it in "Liner Switchercad III" which is free
http://www.linear.com/designtools/software/

Details:

• In the first simulation I have the 1k 'Pot' set to have 700R to +5V, and 300R to GND (This shows the adjustment)
• In the second simulation I have the 1k 'Pot' set to have 300R to +5V, and 700R to GND (This shows the adjustment)
• The 10k resistor (R3) in series with the voltage source V2 (Which is the 'MAP Sensor output voltage') is my rough guess at the output impedance of the MAP Sensor.
• The 100k to GND resistor (R4) is used to simulate the input impedance of the ECU, again this is just a ball park guess.
• The Blue trace is measured at the output of the voltage source V2. i.e. output of MAP sensor
• The Green trace is measured at the non ground end of resistor R4. i.e. input to the ECU.

Cheers
Wilbo

[1jz68u]

there is a guy on supraforums that sells them for $65 shipped. he has done a fair bit of research apparently. comes with instructions and everything.

or you can make one yourself. i had one of these on my 1j worked fine just had to tune it to start with then was all good.

had a problem when i put in a SAFC and was trying to adjust the fuel but thats another story.

[Officer Doofy]

Officer Doofy: 'Better' is a bit of a subjective term , and Craptacular is also interesting...it's simple but does work...please elaborate if you would


Cheers
Wilbo

Geeze sorry to offend Wilbo. I have used both circuits and it was a personal opinion. The things i didnt like about the first circuit are that it reduces the output across the whole range, not just when boost cut is hit. It is adjusted by the pot which is hit and miss for the n00bish user like myself, and the chances of a lean experience are higher.

The second unit leaves the output unchanged to the ecu untill a preset cut voltage. Thus you can connect 5v to it and set a clamp volt as close to the factory cut voltage as you want. It is a much safer unit for the inexperienced user, which i think triptek falls into.

My point was why fuck around with the first unit when there is better ones out there to use, esp on a 2j and i stand by MY opinion of craptacular from my experiences with the pot fcd.

Triptek, maybe pm Placentajaun as he has some good knowledge and personal experiance with the fcd and the 2j.

[triptek]

Cheers for all your guys help, but i'v decided to make one of the diy fcd's in the first post. Just needing some tips on setting it up. Do i turn the pot fully clockwise or anti clockwise to start off with. Do i just keep turning the pot till the car stops fuel cutting.

[wilbo666]

You want to set the POT up initially so that it has the highest resistance between the non 'sensor output' end of the diodes and Ground. i.e. 1k if you are using a 1k pot.

That also means end 'non sensor' end of the diodes to the +5v wire should be very close to 0ohms.

Check with a multimeter to measure the resistance, when the ignition is off (i.e. no 5V power on)

This will have the DIY FCD setup so that it will cut as close to factory boost cut as it can.

Then slowly turn the POT, a little at a time until boost cut no longer occurs
(Try and get it JUST above the engine ECU's boost cut point)

Hope this helps / makes sense

Cheers
Wilbo

[brett_celicacoupe]

ive made 2 units, one is running on my 2jz and another on a mates 1jz.

both work good but i would recommend having 2 pots so that you can get finer adjustment.

set one to say 4V and then connect the other pot between 4V and 5V, it will give better accuracy for setting the FCD voltage.

you should be able to manually set the FCD since the voltage at fuel cut is known. use a multimeter to set the pot at 4.7V (check this)