Hi Andrew

I missed your post or I would have responded sooner. Although I am flattered that you asked me directly for help, I can’t help think that your faith is misguided!

What I would say is, that from your comments about "expecting the frequency to change" in the same sentence that you mention duty cycle, I think you are mixing the two control methods up.

Without trying to teach you or anyone to suck eggs, when looking at a Duty Cycle controlled actuator, the frequency is set & does not alter. In both of your examples there are 8 ON / OFF events on screen in the same time frame. The top image is presumably at idle & the lower image is at high revs & with a lot more going on, the number of ON / OFF cycles is exactly the same. This is known as PWM (Pulse Width Modulation). Modulation meaning "controlled" & the "pulse width" meaning "the width of the pulse" or "ON TIME"

There is another method of actuator control that is easily confused with PWM & that is FM or Frequency Modulation. If your captures where displaying a frequency modulated (controlled) actuator, then you would see the number of events on the screen increase, as the ECU commands a greater effort from the actuator (in your case the fuel pressure regulator). As I said before, yours displays the same amount of events in a 10 millisecond capture at both extremes of fuel pressure control.

Looking at your two captures it is clear that there is a definite difference in the duty cycle. Although it is quite hard to determine by looking at the images alone. Pico does have the facility to display duty cycle as a numeric figure & this helps to see the subtle shifts that can be hard to judge by looking at the waveform alone.

It should also be remembered that there is another factor that effects fuel pressure & that is pump speed. It seems obvious, but I remember looking at a scope trace & wondering why I didn’t see a bigger response in the duty cycle waveform, as I applied the throttle. I had given little thought to the fact that the high pressure pump is turning considerably faster as the RPM increases.

Another method of scoping these pressure actuators is with the low amps clamp. Credit to Frank Massey for this, as it was from him that I learned this method that allows observation of the pressure regulator control effort at much longer time bases. By that I mean, can you imagine trying to observe duty cycle or frequency, on a capture that has 10 or 20 seconds on screen. The amps clamp method allows you to study pressure control in a more useful way.

I am not familiar with the vehicle that you are working on, but the principles are similar across the makes. Is your “Pre supply” pressure confirmed?


HTH

Dave Hill

PS. A cautionary note. As always, my comments are just my own understandings & thoughts. I am no James Dillon & am fairly new to all this myself. Any corrections welcomed.