Okay, we've got a 96 Suburban here that has about 300,000 miles on it, and this is one
of our regular customers' cars, and we wanted to do a state of health on the fuel pump on
this vehicle.
So, what we've done is we've gone into the fuse block under hood and installed this U-Activate
unit that allows us to quickly turn on and off the fuel pump circuit.
It also works pretty well to allow you to analyze the control circuit on that as well.
So I've got another one installed on the vehicle, but if you're not familiar with the GM car,
you'll want to go into your service information and look for that component locator.
So we've gone into a direct hit here and typed in fuel pump relay, and we'll go for the
component locations.
This is a 7.4 liter and fuel pump relay right there located in under hood fuse relay center.
So GM really makes this nice because when you take this cover off, they ID the relays,
so you just lay it out there.
So we've pulled the relay out, we've inserted the connector from the U-Activate unit, and
we've got it plugged into the vehicle.
One thing that we did is we've installed a fuel flow meter, and the fuel flow meter
here, we've gone from the fuel filter out into this unit and then back out to the engine.
And then we're also looking at the current because on the end of the U-Activate unit,
you've got a loop here, and so that is the load for the fuel pump.
So we'll be able to look at the fuel pump current on the scope here.
So I've got the current probe installed, got the PICO all set up, and all I need to do
is hit the on button here and turn the fuel pump on.
And what we're looking for is we're looking for system pressure.
The spec on this is between 55 and 60 pounds, and we're looking for fuel flow at the same
time.
So let's watch what happens here.
So we get flow, initially it went up to about 0.7, and then it quickly dropped down to zero,
and we're making about 58 psi.
The vehicle runs okay, but if we look at the scope here, so let's just turn on the scope.
We see we're drawing about six amps, and let's lower this down here.
About six amps, and we can stop it, and we can maybe measure the time.
So let's pick a spot here, and we've got one, two, three, four, five, six, seven, eight.
So that'll be our second spot there.
And in between those two, we see we're at about 4,400 RPM.
So that pattern looks good, but the problem here is that this thing should be flowing
about, in my estimate, probably about 0.6 gallons per minute, and we're not doing that.
The other thing that happens here when we shut the pump off, you'll see that the pressure
immediately decays, and it's dropping down below 20 pounds there.
So we're theorizing that we've probably got a leak inside the fuel tank, which would explain
the drop in fuel pressure, but no flow.
Initially it comes right up to about 0.7, then drops right off.
So we're going to take the fuel pump out of this vehicle and inspect.
Okay, we've got our 96th Suburban that we tested earlier.
We found that the fuel pump, although it was providing system pressure, wasn't providing
any flow.
And as soon as you shut the key off, the pressure decayed down to about 20 pounds pretty quickly.
We went ahead and sold the pump, took it all apart, we replaced the sender and the pump,
and unfortunately the first pump that we got from this AC Delco genuine pump was defective.
It's an EP381, and it is about 144 liters per hour, about 40 gallons per hour is what
that pump does, and it produces about 61 PSI.
So we put this pump in and it was very, very noisy.
It would produce pressure, the 62 PSI, but it would drop down, it wouldn't flow at all.
So there's nothing being returned back to the tank.
So we took it apart, looked at it, decided to get another pump in it, and we went in
and replaced it, and now we've got everything running well.
So I just wanted to show you that, and so we've got the fuel flow meter installed.
You can see the system pressure is actually maintaining about 49, 48 PSI, and it's been
sitting for approximately, I don't know, 10 minutes or so.
And so I've got the Uactivate unit hooked up here, and I'm also connected to the Pico,
and I've got a current probe on there.
So I'm going to actuate this pump, and then we'll talk about the current.
So let's watch this, okay, pump is on, and you see now we're 62 PSI, and we're flowing
about 0.5, 2.5, 4 gallons per minute, and that's looking really, really good.
And I'm going to go ahead and shut that off, and we'll just go back and look at the scope
real quick here.
And you see our pump, it spikes at about 11.5 amps, and then normalizes here.
And so let's take a look, let's do a measurement of speed, or RPM, to 1, 2, 3, 4, 5, 6, 7, 8.
Right there to that guy right there, all right, I'll verify that, we've got eight in there,
and we're about 3,400 RPM.
So earlier, when we put the first pump in there, we had a very, very noisy 2,600 RPM,
and if we look over here, this is the first one, and then that is, there's our start-up
on the original pump that we pulled out of the vehicle, and it had an internal leak.
The clamps were actually loose around the fuel pump, and you'll see that the RPM here
shows 5,800 RPM.
So it was making the pressure, but as soon as we set the key off, it let all the pressure
out.
So anyway, I hope that this was enlightening at some point, and provided some additional
information.
Thanks.
