I have a 2007 K Series BMW with low fuel pressure (36 psi). It is a return-less system that uses a pressure sensor and a fuel controller that sends a PWM signal to keep the pump at the correct pressure. I have determined that the sensor is reading correct and have checked the pump with it disconnected to check for pressure (75psi). I want to make sure its the controller before ordering as its expensive. I have attached the waveform when the engine is idling. Its about a 43% duty cycle and about 12 volts. Does this seem correct?

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James, Larry here.

I assume this is supposed to be a square wave, never know without looking at another one. You know what they say, need a good one to look at.

What I don't like about it for starters is that ground is below zero That is if the dotted line is zero, don't have the file, not good IMO.

Could assume the on time, or off time, sometimes not what you think, but if PWM would think it go to 12 volts, hold steady there, then go to ground. Again without a known good we won't know.

Larry

Also, for what it is worth, noting the little bumps at about 3.5 volts are not all the same. Some a hair wider and a couple toggle higher than the others, but does look suspicious even if this is how it operates.

James is this module a stand alone device?

This sounds like a good example where we need to verify the whole system.

Powers, grounds, commands, outputs. If the driver module has adequate power feeds, ground integrity, and is receiving the proper commands, and it can't perform its duty, its junk.