On many modern vehicles, OEMs have started using what they call Brushless Fuel Pumps on their vehicles. Now, if you're used to testing an older style Brushed DC Fuel Pump, the test is totally different, and it looks totally different on the scope. So let's check out what it does look like.
Okay, so on these pumps, they use three pairs of windings, and they switch the polarity back and forth in order to make the magnets go around on the inside. I'm connected to this Camry® on all three circuits, plus I have a low amp’s probe so we can see what the current flow looks like as well.
Now, on this screen, it looks a little bit messy, so we need to clean it up a little bit. So we'll go into setup and go to view and layout, and we can change that to a four window view, which now gives us each of those channels separated. Now let's take a stop right there. Now we can see each of the channels, and we'll go through this a little bit, analyze it a little bit. So you can see they're offset actually by 120 degrees each. And that's because to get a 360-degree circle, split it three times, you get 120 degree offset. As each comes on, one will go positive, another one will go negative, and then another one goes positive. And then you'll see they switch polarities. This one goes negative on the end. This one goes positive on the end. This one goes negative on the end.
So they switch back and forth, and that allows them to repel the magnets inside. This low amp probe is connected to channel one, so it goes along with whatever channel one is doing. So I have no current when channel one is not on. I have current that goes up when I'm in a positive state, no current when it's off, and then a negative current when it goes into a negative state as it spins around.
So this is a test you can do. I have it connected in the rear of the car. The fuel pump module is located in the rear on this vehicle. It's a test you can do to see the condition of the fuel pump, the different circuits, are they actually working? Is there current flowing through the different circuits?
You can also do an RPM calculation, which you could do on an old brushed fuel pump. You can still do it on a Brushless Fuel Pump. We just have to think about it maybe a little bit differently. So in order to do that, let's turn on our cursors and show them. Go back. Now, I have them set up here on number one, circuit one. Remember, we have to go a positive and then a negative, and then when it goes positive again. So that's the second time around. So that is one revolution that's contained in between those two cursors. Now, let's bring up my math right down here, and we'll see from there to there one time around, takes eight and a half milliseconds.
So if I pull up my calculator here, it's the same equation. By the way, if you're used to doing this on a Brushed Fuel Pump. So there's 60,000 milliseconds in a minute. Now, if we divide that by how long it takes to turn one time, 8.5, we get my revolutions per minute. In this case, 7058 RPM.
So with this, you can see there are some similarities and some differences between regular Brushed DC Fuel Pumps and Brushless DC Fuel Pumps. Testing was a little bit different, but there are some tests we can do, like that RPM test. So hopefully you got a few tips and tricks out of this.