How is fuel delivery calculated?...

[mattjk]

Not a problem as such just would like to understand my car a little better...

Primarily what factors effect the fuelling of the car and how do they work together I'm assuming the ECU has several different inputs that it uses to calculate delivery such as;

Map sensor - Calculates pressure inside plenum assuming the pressure drops as the butterfly is opened?

Air temp sensor - Colder the air then slight adjustments are made to richen the mixture to enable the correct mixture. Vice versa for hot Ie leans the mixture..

Knock sensor - used to advance/r****d ignition as nessasary. What does a knock correction number of say 3 or 4 mean? Is it measured in degrees or some other fancy measurement.

Lambda sensor - I'm not to sure on this one I though that if the O2 reads higher then it will instruct the ECU to add addtional fuel and the second lambda i used purely for monitoring emmisions?

Throttle butterfly motor - (don't know the tech name for it sorry) I'm assuming that this is set a pre-defined level, ei if its opened more then the the ECU knows to increase fuelling

Coolant Temp sensor - I don't really know how this would effect fuelling although I was under the impression once the engine heats up then the variable valve timing is activated resulting in smoother running fuel economy etc....

If i'v missed anything out or got something wrong please say. I was also curious as to how much more air you could force into the engine before its unable to cope with the extra air? (how much hp is that equivelant too also...)

All this just for curiosity and to get a better understanding (Dont worry i aint got no plans for a 'kuston leaf blower induction kit' lol)

Thanks

 

[GordonD]

...
Map sensor - Calculates pressure inside plenum assuming the pressure drops as the butterfly is opened?

A small correction. The pressure rises as the butterfly opens. What you probably meant was the manifold vacuum drops as the butterfly is opened.

 

[Jay Payne]

lambda sensor is used to detirmine how well the fuel has been burnt. Basicly checks that all its calculations are correct.

When the engine is in first minuite or so from cold the engine is in whats called open loop. The ecu is messuring temp/pressure/ throttle position etc then caluclating, then injecting then the engine burns it, utill the o2/lambda sensor is warm (they have a small heating element in them) it will not give any reading. when its warm it will give the ecu a means to check if complete combustion has taken place, this is called closed loop.

Complete combustion is not possible so the lamdda will read high then low then high etc. switching this is the fluctuation in signal u see on a live reading code scanner. normaly between around 0.1volt and 0.9volts

Open loop = Measure (sensors etc) > calculate (ecu) > Inject and burn
Closed loop = Measure > calculate > Inject and burn > check after combustion (lambda)

2nd sensor on cars after 2001 ish after cat is there to check efficiency of the cat. obviously it will read practicly nothing if the cat is working. This is why when people have a de-cat the light will sometimes come on

 

[mattjk]

Thankyou for the explanation Burp.

GordonD: Surely the pressure will drop when the butterfly is opened as the inlet is being restricted by the butterfly causing a pressure build up. Im sure your right and im wrong but thats just how i interpreted it

Any idea on what the knock correction is measured in?

 

[bmh.01]

The pressure in the manifold drops when the butterfly is closed and it creates a vacuum in the inlet manifold (which is used for the brake servo etc), it does it because no matter what the throttle position the pistons/cylinders are always trying to draw 2l of charge and its obviously much more difficult with a closed throttle butterfly compared to WOT.

 

[mattjk]

Ahh okay i got you. How much can these system compensate? (ei extra air before it exceeds what they can manage)

Jusr remember seeing a leafblower being attached to an intake and made me chuckle i'm assuming it could cope with a small boost.

 

[stan*]

A typical NA MAP sensor will be around 1.1Bar (maybe 1.05bar) absolute (i.e 0.1Bar Gauge). As the engine wont be running 100% volumetric efficiency, then the sensor will experience maybe 0.8bar at WOT. SO "in theory" you could "add on" whatever drop there is in intake pressure at WOT as "boost"...meaning the MAP will read a full 1Bar absolute.

Knock correction will be either %correction factor, or actual degree reduction.
Coolant correction will be zero after say 65deg.C coolant temp.

 

[mattjk]

Thanks stan, i knew one of you clever buggers would know. So there is a bit of leway at WOT still then.

Cheers thats all i wanted to know..