DeanF

iTrader: (1)

The Hks Fcd has a dial for increasing the fuel cut thresh hold. 12 being the lowest setting & 1 the highest. Does anyone know what these numbers roughly equate to in Boost (psi).
Thanx
Dean

john banks

They depend on your MAP sensor and model year.

A sensible approach would be to start at 12 and if you get a fuel cut at your desired boost pressure then reduce it until you don't. If you were then very cautious or were using a fairly imprecise boost control system you might want to turn it one further beyond that to ensure that you don't get a fuel cut when overtaking in cold weather for example as you don't know if the last setting was *just* stopping it fuel cutting.

Please monitor appropriate engine safety parameters when setting this up - there is (obvious) major engine damage potential from using one.

DeanF

iTrader: (1)

Cheers John. Car is My94 UK. I was going to do as you suggested but had heard or read somewhere that when you hit fuel cut the Ecu remembers this & will not let you go past this point until it has done a few million cycles for obvious safety reasons. I suppose once i have reached the desired limit i could reset the Ecu & start on a clean slate as such.
Dean

john banks

I don't know much about the early ECUs, but I believe it remembers knock events and never advances the ignition again at that point, have not heard of the fuel cut memory. Resetting once set up on an old ECU would ensure it has no "bad memories", but I suspect will make no difference.

RICH WILD

Hi, mine is set to 1 and I run 1.5bar with no fuel cut, so it's at least that.

(MY96UK)

Cheers

Rich

john banks

There probably isn't and can't be a fuel cut at all using a 2 bar map sensor and running 2.5 bar absolute Rich whether you are on setting one or not?

Katana

You guys are confusing me. For fueling, isn't the MAF and not the MAP sensor which is the one that controls it? I thought all the MAP sensor ever does is check for overboost? If not, time for another round of tweaking. John?

john banks

Yes, I have not seen any convincing evidence of MAP input to fuelling at any stage with my MY00. Did something above suggest otherwise? Changing the MAF sensor signal alters fuelling and timing. How the Unichip manages to independently adjust timing and fuelling I am not sure - I know it piggybacks the crank position sensor and the MAF, the former only adjusting ignition, the latter presumably adjusting both together - they must have worked out a compensation setup? Fuel cut is a different matter though and mediated by the MAP sensor. Bob Rawle mentioned a MAF cut out as well I believe on earlier ECUs, but I haven't played with them.

[Edited by john banks - 27/05/2002 18:18:28]

Katana

Cheers John. Ever since I managed to lower the MAP sensor's voltage, I haven't noticed any fuel cut from the MAF in my model. Its just my paranoia playing up again.

I've just had a stupid thought, if someone wants to get rid of the overboost cut completely, why don't they just stick on some 100 ohm resistors in series on the MAP sensor signal? The ECU would still detect some voltage. Better yet, get an insanely long and thin cable and connect it in between the MAP sensor and the ECU since Resistance = (resistivity) x (length/Area). And to say I failed electronics.

T-uk

John,

did you not say,that delta dash had showed that your car ran slightly leaner,with the fcd fitted?

john banks

Katana a 6 pence zener diode does the job nicely

John I thought it did at one time but now I don't - I think it is environmental conditions changing - it got hotter and I fitted the FCD - coincidence. The lambda sensor reading depends on environmental temperature it seems as well, despite it being in a hot exhaust gas flow, yes seems odd, but I am not the only one to notice this. May explain why WREXY has the appearance of a lean car.

WREXY

I must say that each delta log that I've done, the ambient temperatures have been over 25 degrees celsius. Today was around 30 deg celsius and my O2 sensor readings were slightly lower at 0.86 volts, with 25 degrees they are around 0.875/0.88 volts.

Even when Mervyn from PE came here and we did some logs it was at least 25 degrees celsius and I was getting around the 0.87 volts area.

Dmel's (scoobynet member) car, a MY99, on a 25 degrees celsius day, with an AE801 ECU, a magnex twin downpipe, scoobysport exhaust (I think), was getting around 0.89/0.90/0.91 volts and I was getting 0.875 volts with an APS cold air induction, 5 Zigen exhaust of 70 mm in diameter or 2 3/4 inch, (midsection and backbox only), FCD, Blitz electronic boost controller and Blitz Bov.

The weather would definately play a role. The bad news is that winter is a very very long way ahead. I can't wait to do some logs then.

By the way I've ordered another MAF just to make sure the one I bought a couple of weeks ago is not a dud.

Cheers,

Wrexy.

Katana

And this is probably why electronics is not my strong point.

Oh well, I'll just stick to mechanical engineering stuff for now. Electronics is far too confusing.

DeanF

iTrader: (1)

Doesn't the 6 pence zener diode elimate fuel cut all together ! Removing the safety margins that can be applied with a Hks Fcd Etc..

john banks

Yes it does, but Katana said, "if someone wants to get rid of the overboost cut completely", so I just told him how he could do it. We did come up with a circuit in drivetrain which uses an op amp, a zener and a variable resistor to raised fuel cut. This gave me a 22 PSI fuel cut (raised about 4.5 PSI) and I was running 20 PSI on my hybrid TD04L as I do now. Why not just use a resistor? - because the atmospheric reading at 2.3 V approx would be shifted too and this is undesirable as the ECU likes to know this accurately - it may just be used for atmospheric pressure compensation for boost control and boost limit, but we don't know for sure so best to preserve it as it could conceivably affect fuelling or ignition and I had no way of testing when I made the circuit. Unfortunately the HKS FCD does affect this value rather more than is desirable http://www.mr2.com/ARTICLE/HKSFCDat.html

DeanF

iTrader: (1)

The Hks analysis makes interesting reading, I must admit i used the zener diode option on my Gt4 which was decatted and just had an adjustable bleed valve,it use fuel cut terribly before the zener. (boost spikes. didn't know about those then)if only i knew then what i know now.