|
|
Normal fuel pump amperage draw on this TBI fuel system (above) is between 3 and 4 amps. As you can see, pump amp draw is excessive. Normal wear and tear on fuel pump innards does not include shorting of the armature windings (I’ve never seen one but they may be out there) so greater amp draw must be due to lower pump revolution speed (a function of CEMF) caused by physical resistance applied to the pump motor. The image on the right is an AC amp waveform and the measured frequency is 0 Hz. Normal frequency ranges from 400 to 600 Hz. This fuel pump is powered up, but not moving.
Next Vehicle
|
|
In this scenario, the pump kicked in after I smacked the fuel tank with a hammer. We could have damaged or poor connections at the pump or fuel-sending unit, however, the amp wave tells us a different story. Once the pump is running, we can see the amperage dropouts in the waveform. There should only be a minor ripple in the waveform; almost undetectable in the current screen configuration. We know this one will need a fuel pump and we should also inspect the fuel-sender connections when we get it apart. |
Next Vehicle
|
|
As stated, the DC amperage drain from this TBI fuel pump was a little over 3.5a. Here you can see the signal frequency is 685 Hz. From these facts, I can deduce that there is fuel in the tank and that the pump is working. I noted on the RO that I thought the pump was fairly new (from the readings) and found out later that it had been recently replaced. So what did I know about this fuel system in a few short moments? That it wasn’t the cause of the no-start condition…. |
Next Vehicle
|
Here is another fuel pump amp waveform from a 1995 Astro Van that wouldn’t start. There is no need to climb under the Van and check for proper voltage at the pump, it’s wasted…. |
Although this has obviously not been an exhaustive study on the analysis of fuel pump amp waveforms, I hope if you were not familiar with them that it has sparked your interest.
For more fuel pump amp wave information
visit: