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So here goes another one. Contrary to some information posted on the board from time to time, the stock ECU does provide two-speed pulse-width modulated control over the stock fuel pump. See the attached. Does anyone know what the exact parameters are? E.g., what the frequency and duty cycle is at idle and part load or how part load is defined?

--Peter
 

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Peter,
Here's a scope trace at idle. Pump current is blue (shown negative because I had clamp-on meter wrong way round), voltage at pump terminals is red.
PWM freq is 120 Hz.
A DVM was also used. On DC scale, voltage was 10.2 V. So duty = 10.2/13.16 = 78%.

Analyzing PW signal, voltage at pump drops to zero, then increases to 5V and holds there for a while (with no current to pump), then increases to ~13V with current ramping up to 14.9A (100 mV/A scale on clamp-on meter).
I don't know why pump module has the 5V hold step instead of a nice clean square wave. It seems to be a high impedance 5V since it's restricting current so maybe a monitoring function?

Picoscope voltage and current 0 to 3000 rpm.JPG

Then at around 3000 rpm, the PWM switches off (rapid change, no transition), and the voltage and current become steady, as shown below, with voltage 13.16 V and current 12.2 A. The pump speed is 5400 rpm as shown by the repeating pattern in the ripple on the current trace. I suspect the switching point is simply rpm as the engine load at 3000 rpm on the driveway is the same as when idling.

Picoscope voltage and current 3000 rpm.JPG
 

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Discussion Starter #3
Peter,
Here's a scope trace at idle. Pump current is blue (shown negative because I had clamp-on meter wrong way round), voltage at pump terminals is red.
PWM freq is 120 Hz.
A DVM was also used. On DC scale, voltage was 10.2 V. So duty = 10.2/13.16 = 78%.

Analyzing PW signal, voltage at pump drops to zero, then increases to 5V and holds there for a while (with no current to pump), then increases to ~13V with current ramping up to 14.9A (100 mV/A scale on clamp-on meter).
I don't know why pump module has the 5V hold step instead of a nice clean square wave. It seems to be a high impedance 5V since it's restricting current so maybe a monitoring function?

View attachment 480785

Then at around 3000 rpm, the PWM switches off (rapid change, no transition), and the voltage and current become steady, as shown below, with voltage 13.16 V and current 12.2 A. The pump speed is 5400 rpm as shown by the repeating pattern in the ripple on the current trace. I suspect the switching point is simply rpm as the engine load at 3000 rpm on the driveway is the same as when idling.

View attachment 480793
Wow. Precisely what I needed. Thank you so much.

5V high impedance step is indeed weird. I don't think I will emulate that!

--Peter
 

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Has anyone fitted a fuel cooler to the circuit? If you have ever had the pleasure of opening the fuel tank after a spirited drive you will know that the fuel in there even on a mostly full tank is too hot to put your hand in there comfortably. I presume this is why there is pwm on the pump as it reduces heat generated by the pump. Also cleverly the fuel return is low pressure too so to avoid unnecessary heat from pressurising fuel when not needed.

I was thinking of a small fuel cooler, just not sure what the standard push fit fuel pipe connectors are so I can buy some.
 

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Sorry can't remember exactly but the fittings are the exact same as either ford or chevy, might have been both. The locking method was different in nature, but were identical in size on the inside. The lock part is larger to allow for release tools but receives the BMW male end perfectly. If the male ends are the same then they are the same in my book.

The unlock slide is included with the BMW system but on the American version you use a tool to open the clip. The latter is preferred as the plastic release does not break. The tools for release come in two versions at least with some very trouble free tools. Mine claps both sides auto adjusting to the hose size, first pushes the tubes together then pushing in the release slide , then pulls the tubes apart all in one easy squeeze like pliers. Most of my work was on fords so likely that was the twin, but chev and BMW share parts frequently.

The easy way to figure it out is go to the parts store with filter in hand and look at either a ford or chevy. You will likely find that it is a standard used in many things rather than exclusive to a few uses.
 

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I will add not sure it is a good idea. We used to run the fuel through the rail to heat it up to a consistent temp for better ignition but this causes more fuel vapors to the tank which causes the enviro guys to go nuts. This is why the change was made to reduce fuel vapor not because you get better performance. I would imagine there is a delicate line and fuel needs to be hot to perform at its max.
 
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