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Master Injector Pulse width for initial start up?

Practical Standalone Tuning

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Please can the community provide some clarity on the following:

Im reasonable new to the HPA tuning community so please bare with me...

Andre gives many examples in the Practical Tuning Course of how to setup values in the Fuel table for cars running ecu's with a Modelled VE approach.

For the initial start up stage of the HPA 10 step process, the Target AFR table has been decided upon, and then the Base Fuel table is set globally to around 50% VE with MAP on the load axis. The ignition table is usually set globally to around 15deg of timing. I understand all this.

What I need help with understanding is situations where you have an ECU that uses Tradtional time based Fuel Tables instead of a modelled VE approach. For example the Link G4+ / G4x. I have watched the Webinar (i think its no.11) and understand the concepts around settting Master Pulse width. That the Values in the base fuel table are then a 0-100% value of this master pulse width (@100kpa) and its effect on Resolution for appropriate fine tuning of fueling around important areas of the Map such as idle etc. But you need to have Mapped a Fuel Table already and then go back and adjust the Master Pulse width to provide better Resolution in the Fuel Table.

But what if your just starting?

How do you decide upon a value for Master Pulse width for the intial start up? What values do you initially enter gloabally in the Base Fuel table?

As a Tuner do you need to work out roughly what the mass airflow into the engine would be at 50% VE and then work out based on injector flow and your target AFR how much fuel needs to be injected roughly and go from there?

Theres variables to consider..non linearity of injector flow vs duty cycle.. variables in engine VE especially if its a forced induction engine rather than NA..

Please could you suggest a way forward for traditional fuel tuning similar to the VE approach, because to me at the moment the Traditional Fuel Tuning Master Pulse width value seems like a bit of a 'Chicken and Egg' situation.. pick a value and tune from there :(



The master fuel value is just a scaler, It is not really important. If your master is on the small side then the fuel table numbers will be on the bigger side, if your master is large then your fuel table numbers will end up small. You dont want your fuel table numbers too small as it will mean you have less resolution at short pulsewidths. There is obviously a limitation on the largest number as well (150% from memory). The help file suggests to aim for numbers of around 50% in the middle of your fuel table, but that is just a guide, it is not critical, anything from 30-80% will work fine.

A quick way to get a suitable master fuel number is either start with a fuel table out of one of the Link base maps which will have a range of numbers in it something like 30-70% or just wack 40% in the whole table and bump the master fuel number up or down until the engine starts and runs. Your master fuel number is then good and you can then tune the fuel table from there.

The Master fuel will vary with injector size, fuel pressure, cylinder size, and stoich ratio. Here's some ballpark numbers just as a guide, assuming 3bar fuel press, 500cc/cylinder, petrol fuel:

1000cc inj = 7-10ms master

500cc inj = 14-18ms

300cc inj = 24-30ms

Thank you Adam,

your postis very helpful:)

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