strange fuel pressure behavior when using pwm

[Yves]

I proceeded testing my ford FPDM to regulate the speed on my Aeromotive A1000. The FPDM actually reduces the pump speed as I can hear it actually slow down, but I can only get about 4 - 5 psi of pressure drop even when going to about 20% of maximum speed.
My fuel system consists out of a normal return style system but with a fuel sump tank installed in the engine compartment that is fed by a low pressure pump.
Before you ask : pressure drops fairly quick after shutting both pumps down so this isn't an issue related to the fuel lines or so. (Aeromotive FPR has a quick bleed down rate as is already discussed here).

Not sure what to do as I was expecting more adjustability in pressure but maybe someone knows if there is something else I'm overlooking right now.

[billr]

Is that a turbine pump or positive-displacement? How do you know the pump is going down to 20% speed, do you have a way to measure rpm of the pump?

[Yves]

Is that a turbine pump or positive-displacement? How do you know the pump is going down to 20% speed, do you have a way to measure rpm of the pump?

No, it's the % of pwm I put into TS during open loop control and in the cell it was running in. I could hear the pump speed go down quite a lot.
Conventional pump I believe, not positive displacement. However, I cannot find any info on it.

If there is a good way to measure the pwm I'm all ears.

[billr]

"Many Aeromotive pumps are of the “non pressure limited” type, including the A1000 for example. This type of pump cannot be used with a static (non bypass) regulator, because to stop the flow coming from the pump completely would drive fuel pressure to 100-PSI or higher,"

That is an excerpt from the Aeromotive FAQs, and implies that the A1000 is a positive-displacement type (what I would call a "conventional" fuel pump). That kind of pump may well require a very low rpm/PWM to maintain pressure when the flow is low or zero. Such a pump should still be able to work with closed-loop control, but it may get iffy at very low flows. At the low speeds required at low flow, the pump internal friction (brushes, etc.) may start to predominate and cause the control system to be very tricky to tune.

I am making some generalizations (and guesses), but am kind of confirming Aeromotive's advice that this pump should be used with a relief-type FPR that lets the flow keep going at a normal rate for the pump.

[Yves]

I think you're on the right track. Not sure how I'm going to deal with this. Didn't quite expect it.

[Yves]

Coming back to this. I got it working

Stupid mistake : had the fuel control set to open loop and put in a value of 20% in the field it was running in, but MS also looks at the fields besides it and those were still at maximum speed.. Once I set all of them to 10% the pressure dropped.
I can even run it in open loop now.

[Yves]

Coming back to this : I managed to set up a gauge to monitor the Fuel pump duty in TS. Turns out that in closed loop it runs the pump at full power whereas in open loop I can actually command the required pw. Not sure why the closed loop function wouldn't do the same however. Even when using a higher setpoint on the FPR, the ecu doesn't bring down the pressure. Also when disconnecting the vacuum tube to the FPR, it should normally correct for this all by itself which it didn't do.