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Master Fuel, Minimum Effective Pulse Width

Rob W

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Long story but when my g4+ was originally tuned in my 99 wrx I did not have the manufacturers minimum effective pulse width wich is 1.5ms. We used a figure of .9 and adjusted dead times to suit. There are some issues with idle and time for the engine to go into fuel cut after lifting off the throttle.

I added the correct deadtimes and min pulse width. The car dropped 4 afr's at idle from around 15 down to 11 and was stable. My plan was to change the master fuel to suit and was hoping to get reasonably close to the afr's through the map already on the car. Master fuel though is having no effect either up or down. Have I misunderstood this function or is there something else I'm missing. I tried on both opn and closed loop idle.

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You have set to long minimum pulse width

It mean that injector will be opened at least for 1.5 msec per cycle

NOT shorter!

If you check current injector pulsewith you can see it always 1.5 ms on idle

and untill you make master fuel big enough that ECU will calculate injector pulse width more than 1.5 msec AFR will not change


Master fuel is very important parametr

if you change it - it will affect AFR in entire range of RPM and load




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Hi Rob,

Have a look at the parameters for 'Inj Actual PW' and 'Inj Effective PW'. These are found in the left hand column of the fuel tab of the Runtime Values Window (F12 key to open).

The actual pulsewidth is the effective pulse-width plus the injector deadtime.

Have a look and see what value the pulse-widths are when the AFR is rich. Then monitor them as you reduce the master fuel number. You will not be able to go lower than the setting you have for Min Effective PW.


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