When the truck is running there is a constnat high pitched whine from
the rear end. Might be a fuel pump. I've got 124K miles and wondering if
this is getting ready to go out or can this go on for year. Basically,
How can I tell if its time to change out the fuel pump and if you have
any tips for the replacement if necessary?
Thanks in advance
Just hope you keep hearing that whine. When it stops the pump has
failed. I have had folks who complain about the noise who have a new
pump installed and discover that the new pump is even louder!
Run a fuel pressure test on it and change the fuel filter and you should
be OK. If you have a scope you can actually look at the waveform from
the pump and the amp draw and get a pretty good idea of the actual
condition of the pump. BUT most folks don't have those tools.
I do have an oscilloscope. Are you talking about scoping the Power or is
there a pump pressure signal that I can scope. If so, which connector do
you scope on and what range am I looking for. I also have a ODBC-II
reader but all I see that might be related to fuel pressure is;
- Fuel Level
- Fuel Level Sensor
- Fuel System Monitoring Status
- Fuel Tank Pressure
- Fuel Trip Cell
Is fuel tank pressure the fuel rail pressure or the pressure inside the
You'd be scoping the -current- in the fuel pump circuit, for that you'll
need a low amps probe.
You can scope anywhere in the fuel pump electrical circuit since current
is the same throughout the circuit, often, the most convenient place is
the fuel pump fuse, pull the fuse and substitute a fused jumper wire
long enough for you low amps probe to fit around.
As for what you're looking for; that could get quite long and without
the ability to post binaries to this group, it would b hard to do the
DAGS on "fuel pump+current ramping."
This link should get you started;
DO NOT fall into the trap of chasing the scope! Learn what effects
scope patterns, learn that there is no such thing as a right pattern and
a wrong pattern, everything has to be interpreted and all factors
In the case of the fuel pump. If you jumper the fuel pump fuse, and use
a low amp probe you can watch the waveform as each of the commutator
poles connects with the brushes. What you want to see is a nice steady
sawtooth pattern. Steady means that each section of the rotor is using
the same amount of power and that the brushes are making good contact.
What you don't want to see is a series of pulses with a gap or with a
high spike. Either one means the pump should be replaced. The gap means
that either the rotor wiring has opened or that the commutator bars are
faulty. The high spike shows either a short in the rotor or burnt
commutator pads. These are the ones that you find when the vehicle
quits, BUT you hit the tank hard and the pump works again. It stopped on
the faulty section, same thing as the old "starter dead spot"
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