Megasquirt Required Fuel

[wildo105e]

Thought i would start a thread on this as i don't fully understand it and maybe someone can explain it and help others aswell.
My simple theory on injection is that you have an injector that is sized to you engine in flow rate fuel is pumped down them at a fixed rate and you decide on an engine cycle how long the injectors are open to produce a good mixture of 14.7 afr ( i said it was simple).

In MS you can run the calculator to work out the required fuel and this helps generate a basic fuel map. If you lower the required fuel and rescale the ve table the figures go up in value :confused: I assume this just gives you more scope to reduce them. What confuses me is that the ECU has no control of fuel pressure etc so you still have the same injector and fuel pressure etc as before now just opening longer but you can reduce this as you have more adjustment i assume there is more behind all this :help:

[Tinde]

I think you're about right, no need to be confused. :)
I've used decreasing reg_fuel and increasing ve-table, as my Escort was running very low ve's at idle with calculated reg_fuel, which made the idle tuning bit rough.


From MS1-Extra tuning manual:

Required Fuel – (Req_Fuel) this is top field of the Constants window. It has a calculation dialog to help you find an appropriate value. It should contain the injector pulse width, in milliseconds, required to supply the fuel for a single injection event at stoichiometric combustion and 100% volumetric efficiency.

Re-Scaling the VE and Req_Fuel - If you have already started tuning but feel your Req_fuel is making the VE table too big or small then you can change the Req_Fuel but you will need to re-scale the VE Table too or the whole table will be out by the percentage of the change in req_fuel so your engine will no run like it used to. Re-Scaling is acheived by going into Basic Settings - Fuel Table 1 then select Tools - VE Specific - Reset Req_Fuel
e.g. VE table full of very low numbers (idle is around 15 and WOT is around 60-70) but drives well and AFR's are correct, then try decreasing the req_fuel value.
In this example we have dropped the req fuel from 14.7 to 12.2, this is roughly a 18% decrease in size, so the whole VE table will be increased by 18% to compensate.

http://www.msextra.com/manuals/MS_Extra_Tuning_Manual.htm#ve_rescale

[wildo105e]

Thanks Tinde. What i still struggle with is if i reduce the req fuel the rescale the ve table do i have effectively have the same fuel being injected but with a higher figure in the table thus giving me more scope to reduce it down If this is the case does mean the rq fuel is used purely for calculating the table.

If you reduce the req fuel without rescaling does this effectively lean the whole table:confused:

[Tinde]

Thanks Tinde. What i still struggle with is if i reduce the req fuel the rescale the ve table do i have effectively have the same fuel being injected but with a higher figure in the table thus giving me more scope to reduce it down If this is the case does mean the rq fuel is used purely for calculating the table.

If you reduce the req fuel without rescaling does this effectively lean the whole table:confused:

As far as I know, yes.

[alladdin]

yes, i also see it as that. (i asked the same question as i recal:D)

you are effectivly simply rescaling the "graph" .
does this mean that the ve values themselves dont actually represent a % of injector open time ?


its been a while since i read any ms related info:dunno: