Fuel cut disabling strategy

[ADL Mark]

Essentially option B is fine for a MAF car like a UK Supra as it is just rescaling the MAP sensors output voltage. The UK ECU doesn't pay any attention to this for fuelling, it uses the MAF which has nothing to do with fuel cut. By the look of that diagram it also never lets the MAP reach it's fuel cut voltage, it stops just before it.

 

For a car that solely runs a MAP sensor like the J-spec Supra, that is bad as MAP sensor voltage and therefore air pressure reading will be telling the ECU the wrong things and will cock up your fuelling slightly. Hence, option A should be used as it keeps the signal the same until fuel cut needs to happen then stops it just short of the fuel cut voltage and caps it (i.e. 4.8V instead of 5V).

[xxcat]

It rescales the output voltage of the sensor against the pressure it sees....

NO - the options was about MAF scaling, not pressure sensor (MAP) But after that Ian told me that only MAP sensor will initiate fuel cut... So I will not scale MAF output! Only MAP (with greddy FCD)... Please read more carefull..

[ADL Mark]

In which case replace pressure for airflow

[Ian C]

It rescales the output voltage of the sensor against the pressure it sees. So that for instance if before 1.2bar = 5V now 1.2bar= 4.5V and 1.6bar = 5V. It's got nothing to do with injector duty.

 

That's slightly misleading, I think if we take the actual stock MAP sensor and describe that it'd make things clearer. The stock MAP sensor reads from -1.0bar to +1.25bar, although that last 0.05bar can't be relied on, it gets quite erratic up there. So it'll never read 1.6bar. The box of tricks sits betwen the MAP sensor and the stock ECU and changes the outputted voltage. If you scale it to the point where reaching the maximum output of the stock MAP sensor - 4.85v (1.20bar), doesn't hit fuel cut, you need to drop the voltage to 4.40v or 0.95 to 0.98bar of boost (yes, if fluctuates a little bit). This is a scaling factor of about 10%. However if you then see, say, 1.4bar of boost, the stock sensor clips at 1.25bar, still spits out 4.85v, and still gets scaled back to 4.40v. So once it's at 1.2bar that's yer lot unless your piggyback ECU has it's own MAP sensor that can read beyond 1.2bar and use that instead (like the E-Manage has and the sAFCI or II certainly doesn't, which is why I've never understood how people can think they will fuel properly past 1.2bar. Anyway.)

 

For a car that solely runs a MAP sensor like the J-spec Supra, that is bad as MAP sensor voltage and therefore air pressure reading will be telling the ECU the wrong things and will cock up your fuelling slightly.

 

More than 'slightly', actually by at least 10%, depending on how it's set. So your 11:1AFR suddenly becomes just over 12:1. Could be nasty.

 

Hence, option A should be used as it keeps the signal the same until fuel cut needs to happen then stops it just short of the fuel cut voltage and caps it (i.e. 4.8V instead of 5V).

 

Yes, but 4.40v or thereabouts is the place, the sensor never even gets to 5v And as I've said before if you are capping the voltage signal to this level, your injectors are now running 100% duty up the top of the rev range.

 

-Ian

[Ian C]

NO - the options was about MAF scaling, not pressure sensor (MAP) But after that Ian told me that only MAP sensor will initiate fuel cut... So I will not scale MAF output! Only MAP (with greddy FCD)... Please read more carefull..

 

I'd still scale the airflow output as a course tune but that's just me.

 

-Ian

[xxcat]

I mean I will not scale it just to avoid Fuel Cut... But I think I should alter it's map for proper injection/timing.

And I'll use non oem MAF and at least 3bar MAP with emanage. I don't want to get rid of MAF by now