Popping noise at low PWM % on fuel pump

[vw_chuck]

I was running my fuel pump at around 20% PWM in tests mode and found that I was hearing a popping noise coming from the fuel pump?
Any idea what that could have been? Anyone seen this before?

[Paul_VR6]

What kind of fuel pump and what frequency and what driver arrangement? My weldon doesn't like under 30%.

[vw_chuck]

Its an 044 with a Dorman 902-310 SSR running it. My guess is it is stalling the pump or something at the low PWM. I think it is 39hz I was running it at mostly. It did it pretty much on all the frequencies. I tried 78,19.5,2?, etc..

[wes kiser]

I certainly wouldn't even try something as slow as 39hz. I always select the fastest possible frequency for things that are not necessarily designed to be pwm'd. The pump is attempting to start/stop at that frequency. The faster you do this, the "smoother" this affect. Most dedicated PWM pump controllers are a much faster frequency than the 300 or so HZ you have available.

That being said, if frequency doesn't change the noise (or even if it does) I simply would not command a duty cycle that made the noise (or honestly anywhere close to it).

[ArttuH]

Roller cell type pumps like Bosch 044 just won't work with too low duty cycle. Or to be more technical, you can't reduce fuel flow below certain threshold. If you go below that threshold all kind weird things start happening. The pump may lock up, consume more current, oscillate or whatever. For example with Walbro GSL392 pump I couldn't go lower than about 40% PWM at 3 bar base pressure.

Turbine type pumps allow wider control range and they can work even at zero flow.