Jaycar Fuel Cut Defender

[JOHNNNY]

i have just been looking at a fuel cut defender for my s2 stag and i came across one made by jaycar , it isnt adjustable like a turbosmart model but in the discription it said that it dosent need to be ! . so im just wondering if i could get any advice on it as it is only 19.95 for the chip and $4 for a housing . ??????????? and yes i know a good one is only around 100-200 to buy im just thinking that if it does the same job CORRECTLY AND SAFELY then why pay another $175 for a sticker

here is a pic of the jaycar chip .

[KiwiRS4T]

The price is right but you won't know if it is doing the job correctly and safely unless you have your afrs checked with a wideband meter. If you are planning any further mods save up for a Nistune chip so that you can really tune your engine.

[JOHNNNY]

thanks kiwirs4t i know about the nnistune chip but atm i havent got the 1200 for it so i was looking for a fuel cut defender for the time being just to have it running smoothly til i can get the funnds for a nistune. when you say checked with a wideband meter what do you mean ?? im looking at fitting it and then running it on the dyno and checking and adjusting the boost / timing a bit more . also i have fitted a air/fuel raito gauge for peice of mind too

[QWK32]

thanks kiwirs4t i know about the nnistune chip but atm i havent got the 1200 for it so i was looking for a fuel cut defender for the time being just to have it running smoothly til i can get the funnds for a nistune. when you say checked with a wideband meter what do you mean ?? im looking at fitting it and then running it on the dyno and checking and adjusting the boost / timing a bit more . also i have fitted a air/fuel raito gauge for peice of mind too

he means check it with a Wideband Air/Fuel sensor which is much more accurate than the stock O2 sensor. you say you have fitted an air/fuel gauge, i'm guessing its not a wideband setup and i wouldn't use that gauge as any real indication of an AFR.

as far as checking it goes, by fitting a fuel cut defender you clamp the MAF signal voltage at a set level so the ecu doesn't think you have gone over the fuel cut limit. but what you also do is stop the ecu from feeding in more fuel to match the increased air flow above the clamped value, which could mean leaning out. now if your running stock turbo and you dont clamp the signal too low you should be right as the stock ecu runs richer than needed. but it wouldnt hurt checking the AFR just for a piece of mind.

[Tommy Kaira RL]

I found that FCD useless on my r33 to start with until I made a few changes to the circuit. For starters when the car idled it was running rough. After putting the circuit on a test bench at work the op amps wouldnt work below 1.2 volts. eg when im idelingthe AFM would put out 1.0v and the ecu was seeing about 4.5V. Changed the chip to a LM372 it dosent have an offset of 1.0v. and I also changed one of the resistors for a variable resistor so I couls change the cliping from 3.9 to 5.0. The circuit was designed for a wrx if you read the instructions. After I got the car on the dyno after the mods the FCD was set to 4.5 volts on the output.

[KiwiRS4T]

Brad sounds like he knows what he's talking about.Perhaps you could get him to make it for you unless you understand that electronic speak (I don't!). If you were planning to put your car on a dyno then they should have the proper wideband afr meter to do the settings - your guage if it is running of the stock O2 sensor won't do.

[DaveB]

What's this about the Nistune costing $1200??? Mine cost around $400 and that was the price installed in my ECU, including express post of my ECU back to me.

[pixel8r]

Think about what you want it for. Whats happening is that the Air Flow Meter is reading too high so your ECU cuts fuel to protect your engine. The Fuel Cut Defender simply stops the Air Flow Meter from reading this high (it doesn't change the amount of air actually entering the engine!!) so essentially it is bypassing this safety mechanism.

You are then relying on the factory tune being overly rich so that it will still provide enough fuel once the FCD reaches the clamped voltage. With the FCD on a factory tune it will run rich up until the AFM reaches the clamped voltage (as set on the FCD) and will start to lean out from there. You need to check your AFR's (ie. on a dyno) to make sure your it doesn't lean out to far on the top end. To put it another way, once the revs go above the point where the FCD clamps the AFM voltage, the engine will be getting more air but no extra fuel.

Think of the FCD as a band-aid, not a tuning option. It doesn't just get rid of the fuel cut. It bypasses the ecu's safety mechanism, potentially allowing it to run lean. If you're only flowing slightly more air than stock it should be fine though, provided it works as advertised.

[JOHNNNY]

Think of the FCD as a band-aid, not a tuning option. It doesn't just get rid of the fuel cut. It bypasses the ecu's safety mechanism, potentially allowing it to run lean. If you're only flowing slightly more air than stock it should be fine though, provided it works as advertised.

i also have a FMIC on the car and that is when the fuel cut off problem started

i dont realy want to go too much further with the power atm im just not liking the anoying cut off . and as for boost im realy only looking at about 10.5-12psi at the most for now. currently the car is running 9psi to stop the problem which occurs when boost is turned up anymore than 9psi .

[pixel8r]

Pretty sure its only related to the Air Flow Meter signal. The ecu reads the amount of airflow and if its above a certain limit then it tries to protect the engine by cutting ignition. This is pretty normal because obviously the AFM can only operate within a certain range.

I'd recommend looking for a 2nd hand Apexi SAFC2 and getting that installed and tuned. It works similar to the FCD as far as altering the AFM signal but allows much better actual tuning. You can use it to lean out the mixtures right across the revs, as it uses up to 8? control points and interpolates the amounts between those. So basically it can modify the voltage signal returned by the AFM so that when you're doing say 3000rpm it can do -0.1 and when you're at 4000rpm it can do -0.3 and when you're at the redline it can alter it by -1 for example.

This then tricks the ecu into thinking there is less air going in than there actually is, and so it supplies less fuel. It MUST be first tuned on a dyno to make sure you're not altering the AFM signal too much and running into detonation problems. Its much better than the FCD because you can use it to actually tune how rich it runs right across the rev range.

The result of either SAFC or FCD will be similar as far as your maximum airflow limit before it will either run lean or hit "fuel cut", but the SAFC lets you do much more than just set a limit on your AFM. The later SAFC2 also has a knock sensor I believe.

Hope you get it sorted out.

[JOHNNNY]

thanks guys for all your input ! i think my best option is to go with the nistune ecu . thanks to DaveB for shedding more light on how easy the nistune is to get up and going then all it need is refitting the ECU refitted and a tune on the dyno and its done !!!!! TOO BLOODY EASY . i will keep everyone updated on how it works with pics and details on the upgade , hopfuly within the next month or so !!

[DaveB]

Looking forward to it... you might find you have more power too, if it means you can run a few more PSI boooost

[JOHNNNY]

gotta love more BOOOST !!!

[toneski]

hi ive done the research and the jaycar fcd works only on map not maf, and its not adjustible