Ea82t Dissys

SCOOBIDOO · Post by **SCOOBIDOO** » Sat Apr 25, 2009 4:16 pm

Un-intentionally, my fuelling idea was more suited to the 4 plug ecu,.. RPM + Air Flow + Fuel Map = Fuel Injected
I simply forgot you were takling about the 3 plug ecu,... RPM + Fuel Map = Fuel Injected

Sorry to have upset you

Gannon

Here is something your above formula does not include.
the ea82t use,s air also to govern the fuel in?
Thats why there is an air flow meter fitted.

Gannon · Post by **Gannon** » Sat Apr 25, 2009 5:12 pm

SCOOBIDOO wrote:Here is something your above formula does not include.
the ea82t use,s air also to govern the fuel in?
Thats why there is an air flow meter fitted.

The 4 plug ecu uses information from the air flow meter all the time, from idle right up to redline at WOT. It then uses this information to work out the amount of air being consumed by the engine. It then calculates (with reference from the stored fuel map, temp sensor ect.) how much fuel is required to achieve the desired air/fuel ratio.

The 3 plug on the other hand only uses the air flow meter during idle and cruise. The moment you stomp on the pedal (activating the throttle load sw) or when the turbo starts producing more that 2psi of boost (activating the boost sw) the ECU ignores the air flow meter (because a flapper afm cant read large volumes of air accurately) and uses a cross reference of RPM and the stored fuel map to meter fuel to obtain the desired air/fuel ratio.

This means the 3 plug ecu cant respond to increases in boost in the same way as the 4 plug can.

Please note. This information is based on my research only, if i am incorrect, please dont hesitate to inform me otherwise

discopotato03 · Post by **discopotato03** » Sat Apr 25, 2009 8:09 pm

Gannon to my way of thinking vane and hot wire (meaning MAF or mass air flow) meters do a very similar kind of thing but by different methods .

The Vane type airflow meter is literally a gate or door on a hinge , the more airflow through the device the further the vane opens until it reaches full open . Under the plastic cover on the "hinge pin" is a wiper which runs through an arc over a pair of tracks and gives an increasing voltage signal between closed and fully open .
What the vane can't tell is the temperature of the incoming air so inside the meter body is an air temperature sensor who's signal the computer needs to calculate the airs density .
What you say about the Vane AFM systems control becoming two dimensional when the vane is fully open goes with everything I've read .

The Mass Air Flow meter does the same things but how it measures air temperature and therefore density is different .
My research leads me to believe that MAF sensors have what is called Wheatstone bridge circuitry to maintain the heated wires temp , it sounds to me like the current regulation to keep the wire at X temp is what is used to output a voltage signal ie 1-5 volts to tell the computer what the mass of the incoming air is so it can maintain a regulated air/fuel ratio meaning X mass of air to Y mass of fuel = desired AFR .
MAF meters can run out of flow ability and then the signal output voltage tops out and doesn't get any higher .

The reason why most aftermarket engine management systems use MAP sensors is so you can lose the AFM , not because its a better system .
A MAP sensor can read off small medium and huge engines provided there is adequate pressure signal downstream of the throttle/s .
I know some people swear by MAP load sensing but what screws it up is that inlet manifolds are primarily designed to flow/feed charge air and manifold pressure is not always a good indication of actual air flow .
Engines with individual throttle valves per cylinder (ie RB26 or GTiR spec SR20DET) don't work so well with MAP sensing because you don't have to open the throttle plates very far for the manifold pressure to rise to atmospheric . From that point until the manifold pressure goes positive the MAP sensors voltage output signal flat lines - two dimensional control again .
Airflow meters (either type) will output a rising voltage signal whilever airflow increases up to their maximum .
Progress is slow but aftermarket computers are now being sold that can run off MAF sensors , Apexi PFC was an early one and the Vipec is a locally made later option .

Skylines like mine (R33 RB25DET) don't have to be warmed up very much before they run out of airflow meter . The usual fix is to use a plug in Apexi Power FC (PFC) computer and wire in a 300ZX Z32 twin turbo MAF meter . You also have the option to buy direct fit Nismo (Denso) 555 or 740cc injectors to replace the std 370's .

I am open to anyone's interpretations , I don't know everything .

A .

Gannon · Post by **Gannon** » Sat Apr 25, 2009 9:20 pm

Ah good, we are on the same wavelength.

Yes the reason that the flapper afm cant be used for full load calculation is that the flap reaches full open well before redline. Its near impossible to design a mechanical flap to provide sensitive voltage variations at idle, as well as measurable movement at high load.

The hotwire sensor (which yes contains a wheatstone bridge) also has it limits, but they are outside the engines normal operating conditions. The limitations of the hotwire sensor are usually only reached when boost is increased and the AFM reaches maximum voltage (10v for the EA82 MPFI), signaling the ECU into 'Fuel Cut'
Ive seen somewhere that 'fuel cut' for the EA82T is somewhere between 12 and 14 PSI

discopotato03 · Post by **discopotato03** » Sun Apr 26, 2009 9:18 am

Gannon I don't look at it so much as more boost , more airflow IMO .
On virtually all OEM systems the air flow meter is upstream of any turbocharger/supercharger so the air it meters is under (in theory) atmospheric conditions .
I think what the manufacturers want the engine management system to know is how much air the engine would be taking in if was a larger NA one rather than a smaller forced induced one .
It has to be able to cope with the higher combustion temperatures and pressures to minimise detonation .

As per the two dimensional control , it works ok on a std system but it does make mixtures at the upper end fairly rich - like in Nissan turbo systems of the day ie Z18T's and FJ20ET's something like 10 to 1 AFR .
Once you use non std turbos or greater than std boost pressure more air goes in and if nothing else is changed the AFR will rise (get leaner) and that is not a huge problem - to a LIMITED degree .
The main problems that arise are things like increasing turbine inlet pressure and exhaust gas temperature , the pressure between the exhaust valves and the turbine are almost always higher in OEM turbo systems than inlet manifold pressure . When people just "screw the boost up" they don't realise that the exhaust side pressure is rising out of proportion to the compressor air pressure , the danger is that they then think its only hot air causing detonation - not exhaust gas reversion into the combustion chambers in the valves overlap phase .

This is probably going a little deep for most on a Sunday morning but think about this , if you can get your engine to make better use of its air and fuel in the low to mid range you may be able to get more torque where it's needed rather than chasing higher revs and boost to make the numbers . If you can make the engine process more air and fuel more efficiently than the std state of tune lets it you should make more torque within the limitations of the std injectors and air flow meter .
As I see it the ways to go about this could be say larger valves/modified ports/slightly better cams/better headers/turbos/filters/intercooling . The jury is out on raising the static compression ratio but I think what others found years ago (rally spec engines detonating) was because I think the rules made them stay with the std garbage header and Euro spec turbos which are very small and highly restrictive .
They tell me and I have to agree that all factory EA81/82 chambers and ports are dark ages stuff but they do do what they were designed to and that is to make torque at low revs .
That chamber design is not very detonation resistant and I guess that's why none of these engines was ever sold new in a very high state of tune .

I can keep going but all I hear is snoring .....

A .

SCOOBIDOO · Post by **SCOOBIDOO** » Mon Apr 27, 2009 5:40 pm

I always liked watching a good back pedaling....well done boys..it took the both of you to make some sense of it all....well done....baaaaahahahahaha

discopotato03 · Post by **discopotato03** » Mon Apr 27, 2009 6:16 pm

So tell us scoobi , what management system is the water cooled Dak Dak running ?