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
Fuel filter changes every 30k miles let the pumps last a long time. Normal sound for a running fuel pump.
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 tank.
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 subject justice. DAGS on "fuel pump+current ramping."
This link should get you started;
EVAP pressure inside the tank.
Yep. The trick to using a scope on a vehicle is having a basic idea of what you should see before you see it.
Steve,
Why not just give us a hint on what he should see?
Al
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"
Sounds reasonable. Thanks,
Al
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