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Discussion Starter · #1 ·
After seeing a lot of videos on youtube where an oscilloscope is used for diagnostic purposes, I bought a picoscope and a current clamp. As such one of the first things I decided to test was my fuel pump because it is pretty easy to do and there is a possibility of identifying a pump failure pre-emptively. Below is the current measurement I observed of my pump.

E39M5 Fuel pump current
Rectangle Slope Font Plot Parallel

The vertical column is current in amps. As you can see it runs around 15 amps but has an unusual current profile. Typical fuel pump currents are just humps that don't go down to zero. Below I also tested the same setup on a 2000 Toyota camry for reference. I didn't setup the vertical axis to a current clamp when I took the Camry snapshot, but the current is around 8 amps on the camry and more importantly you can see it doesn't drop to zero. I was just wondering if someone knows how the e39m5 pump is controlled and if these current ramps are normal or not. If someone else has done a similar test on e39m5 please share your finding. Would be good to have a database of known good component oscilloscope data for reference.


Toyota Camry fuel pump current
Rectangle Font Slope Line Parallel
 

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I was just wondering if someone knows how the e39m5 pump is controlled
I can give you the answer but maybe you would prefer some tests so you can figure it out for yourself. I have not tested the switch points, it was on my to do list, but never did it. To do the full test you will need a fuel pressure gauge hooked up also.
Watching your scope and the fuel pressure gauge, raise the RPM and note when the fuel pressure rises. At about the same time the scope will give you a different profile. The correlation between the two is what was on my to do list, not hugely important but I think there might be some insight there.
What you are seeing is normal. The test I gave you should work but may not because there might not be enough engine load, but should be. Car is smart but I think it is not smart enough to consider load other than calc load which is a MAF reading.
What you are seeing is normal, and if you only tested with a volt meter you likely will just see a constant lower voltage depending on meter and settings.
 

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Discussion Starter · #3 ·
Sailor,
Thanks for your answer. I did a bit more digging and found this thread (see post #2) Exact Parameters of Stock PWM Control of Fuel Pump
If I would have found this older thread initially I wouldn't have started this one. Basically my fuel pump current observation looks very similar to the one noted by 68FB. It also good to know that below 3K RPM the fuel pump is pulsed but it goes to constant voltage above 3k. Therefore if you want to look at the electrical integrity of the commutator using an amp probe you should perform the fuel pump current measurement above 3K RPM.
 

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It also good to know that below 3K RPM the fuel pump is pulsed but it goes to constant voltage above 3k.
That is the part I wanted to test, I doubt that it is 3K that triggers that, but static 3K is about right. I think the trigger might be the throttles opening. The throttles are delayed on the S62 until a certain air volume is needed or maybe some other load concern. Using the throttle opening would make sense since the throttle opening increases the vacuum to the FPReg and that increases fuel pressure. It would make sense that the instant the throttles open the fuel pump would go to full power and no longer be limited by the FPRelay to keep up with the increased pressure. Easy for engineers to pull the signal to the throttle actuator and maintain full power from the FPRelay. We just have not confirmed that is how it works.
 
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