Im sure its been covered b4 now but im not clued onto how the fuel system exactly works, so I may be lookin in the wrong areas.

What I would like to know is how is the ecu is now operating with newly installed 24# and maf over the stock 19#. For example the injector pulses etc, how are they determined and are they the same as what is programmed for the stock 19#? Does the O2 sensor play any part.

I would like to maximise performance with what I have and I want to try and understand how it all works together.

Sorry if it all sounds twisted! any help would be great

The new Maf sends signals to the ecu so the ecu thinks it still has 19lb injectors. What happens is the ecu, and the O2 sensors think that it is a stock Maf and Stock injectors. That is why the Maf is calibrated to 24lbs.You would also be wise to upgrade your fuel pump, and add an adjustable Kriban FPR, then get it on a dyno, and adjust baseline fuel pressure to get the most out of your current system. Hope it is all going well for you
Cheers
Brett

Thanx for that info, done all of the above beside dyno work just got a few things to finish b4 im ready.

Can the injectors duty cycle (i hope thats right terminology) be upped at all in efforts to get more fuel in or is that where the dyno tune come into it?

you cannot alter the maximum duty cycle, that is built into the ECU (at 80% from memory). There might be ways around this.., but I can't think of any at the moment.


Cheers

[quote="justfordima"]you cannot alter the maximum duty cycle, that is built into the ECU (at 80% from memory). There might be ways around this.., but I can't think of any at the moment.


Cheers[/quote]

Does that mean if the stock 19# were set at max duty cycle of 80% then the 24# will run at same?

Does the duty cycle change? for instance at full throttle as opposed to idle.

yes, the duty cycle is how long you keep the injector open.. umm... let me find a technical explanation... (too early for me to think of one)





So running 24# injectors, on an ECU calibrated for 19#, it takes the 24# injectors a smaller amount of duty cycle, or open time, to inject the same amount of petrol as the 19# (because they flow more).

In effect this makes everything run pretty rich.

Cheers

^ yep.

That's where the new MAF comes into it.

In the "ideal" world - for example, the stock factory setup - the ECU and the MAF are calibrated to suit the 19# injectors.

When switching to 24# injectors, the ideal solution would be to recalibrate the ECU to use the same MAF for the larger injectors.

That's a pain in the a**.

So, get a different MAF which will tell the ECU that it is seeing LESS air at a given load point. The ECU thinks there's less air going in and will open the injectors for a smaller amount of time - which works, because the 24#s will flow a *very similar* amount of fuel in that reduced amount of time to what is required (i.e. what would be delivered by 19# injectors if the MAF signal were same as standard).

You are effectively shifting all of the load points by installing a MAF which is suited to "fool" the ECU into working with new, larger injectors.

Not ideal... but it works!

So would I be right to assume that the larger injectors give the same fuel delivery as the standard injectors?

Therefore the larger injectors have a shorter duty cycle as a result of the increased volume of air intake allowed by the larger maf.