This page has a pasted section from B&G help files under tuning..
http://members.shaw.ca/megasquirt/manual/mtune.htm#pwm
This is because the plan was to have a 300whp turbo charged monster, and were getting last years car
2.0L 16v with ITB's and nitrous
Setting the PWM Criteria
To tune the PWM [pulse width modulation] values for your engine, you need to know what kind of injectors you have- low impedance or high-impedance. If you are running high-impedance injectors(greater than 10 Ohms), then set the PWM time to a number like 25.4, in essence you are disabling the PWM mode. This allows full voltage to the injectors throughout the pulse widths.
For low-impedance injectors (less than 3 Ohms), you need to limit the current to avoid over heating the injectors. To do this, there is a period of time that you apply full battery voltage [peak] current, then switch over to a lower current-averaged [hold] current, i.e. peak and hold. Alternatively, you can add resistors in series with the injectors. See the Injectors and Fuel Supply section of this manual for more details.
To run low-impedance injectors with the PWM current limit mode, you need to set two parameters - the "PWM Current Limit %" and the "Time Threshold for PWM Mode" - both are on the “Constants€ page. The current limit % is the percent duty cycle when the current limit is invoked. The time threshold is the amount of time from when the injector is first opened until the current limit is activated.
Start with 75% PWM and 1.0 millisecond time threshold. Once you get idling, then first adjust the PWM duty cycle down in 1% increments until you notice a change in idle quality (be sure to hit the "send to ECU" button each time you change the value). This is the point where the current limit is too much and the injectors are not being held fully open. Then move the value back up 3 - 5% (for example, if the idle falters at 45%, then put in a number of 48% to 50%) and move on to adjusting the time threshold. Lower the time threshold by 0.1 milliseconds at a time until the idle quality deteriorates. Then increase it 0.3 ms. Adjust the duty cycle and time threshold alternately to get the optimum values for your set-up.
On the car this is very easy to do and only takes a few minutes. At idle the overall injector pulse widths are small compared to their close time, so this will allow you to adjust the values. In other words, adjust the PWM current limit before taking the car out on the street where injector pulse widths become high.
Now, repeat the two steps again until you converge on a set of numbers that work for your set-up. Also, for some setups, 75% may be too low, so they will need to increase this value - same for the time threshold. Use PWM time threshold values greater than about 1.5 to 1.7 milliseconds only with great caution – it is possible to burn out your injectors!
Somebody else doing the same kind of things..
http://koti.mbnet.fi/meelis/auto/ms.htm
Fuel pump: Two K-jetronic pumps in parallel
Fuel pressure regulator: Adjustable, fuel pressure 3.2 bar +/- manifold pressure
Injectors: Low impedance 460 cc/min (@3.0 bar), running in PWM mode (1.1 ms time threshold, 69% current limit). I can cut current limit down to 60%, but it compromises cold starting when battery voltage is lower (from MembersPage/MarcellGal: this must be with motorola MS which does not have proper VBatt dependent pwm-duty. With MS-AVR you can configure the slope of pwm percentage increase as VBatt decreases). Now I have 65% current limit with code V2.982, which has PWM disabled while cranking. Q1 (TIP42) is mounted on the top cover just to be safe.