How do you check duty cycle of a laptop? I have Freescan but im looking for another program if it offers better or more info.

 

Duty cycle = pulse width of the injectors / time is takes for the crank to make two revolutions. Pulse width and crank rev time is expressed in milliseconds.

Example:

If RPM = 6000 rev/min = 3000 injector firings / min = 50 firings / sec

for each firing of the injector, there is 1 / 50 seconds = .020 seconds x 1000 = 20 milliseconds.

If your pulse width at 6000 rpm is 18 milliseconds:

18 / 20 = 0.90 = 90% duty cycle.

In simplified terms:

Duty Cycle = (Pulse Width x RPM) / 120,000

Example... lets say at 6,152 rom you have a pulse width of 17.25 milliseconds:

DC = (17.25 x 6,152) / 120,000 = 106,122 / 120,000 = 0.884 = 88.4%

TTS DataMaster does this calculation for you, but the results look higher than is reasonable. They use "BPW" or base pulse width for the calculation. I'm not sure if they shouldn't be using the actual pulse width, if its different than the base pulse width. It isn't unusual to have DataMaster showing 100+ % DC, for relatively stock HP engines with stock injectors.

 

It says on Freescan "Base PW L" which i believe is the pulse width for the left side. If thats true my rpm's at 5925 have a pulse width of 26 making it 154,050 / 120,000 for a total of 128% duty cycle. With a supercharger would you use the same calculations since i am still using the fmu? I have the injectors and tune ready to go as soon as the snow melts enough that i can get out of the driveway. What exactly is happening and how bad is it?

 

Your FMU changes the amount of fuel the injectors flow by raising the pressure. So it possible that the system is supplying sufficient fuel, with the injectors open basically all the time. An FMU is a crude way to control the excess fuel required by boost.