For a while I have wanted away of diagnosing injector faults on cars without a pressure test point on the injector rail.
I came across the SenX First Look Low Pressure Pulse Sensor and on the web found it could be connected to the vacuum port on the fuel rail pressure regulator. Searching the web I found some info on making a low pressure pulse sensor from a fuel tank pressure sensor as apparently MAP sensors are unsuitable. However these sensors are 3 wire which complicates the construction and looking at the Senx First Look Sensor it is clearly a 2 wire device I decided to try a simple Piezo disc transducer (also called a contact microphone or Piezo guitar pickup) and it worked first time!

This is the 2nd prototype, total cost was less than £2


Low Pressure Pulse Sensor



Pulse Sensor In Use Connected on engine to the vacuum port on a pressure pulse damper on returnless system. It will work equally well connected to a pressure regulator vacuum port.


Oscilloscope Trace --- I later realised it should be invereted to show dips in pressure when injectors open


Fuel Rail Pulse

[Edited on 10/10/15 by britishtrident]

More details of construction


Description

Are you sure your not just seeing the individual cylinder vacuum pulses, rather than injector pulses?. Disconnect an injector and take a trace to be sure?.

Ian

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Originally posted by Oddified
Are you sure your not just seeing the individual cylinder vacuum pulses, rather than injector pulses?. Disconnect an injector and take a trace to be sure?.

Ian

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Link to equivalent "Official" guided test on Pico Automotive web site using a much better scope and a puka First Look Sensor



https://www.picoauto.com/library/automotive-guided-tests/fuel-pressure-regulator-vacuum-vs-ignition

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Originally posted by britishtrident

quote:

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Originally posted by Oddified
Are you sure your not just seeing the individual cylinder vacuum pulses, rather than injector pulses?. Disconnect an injector and take a trace to be sure?.

Ian

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It isn't connected to vacuum the vacuum line is completely disconnected and nipped off. The pulse is coming from the diaphragm in the pressure regulator/pulse damper which with the vacuum pipe removed, only connection that remains is to fuel rail pressure via the damper/. Ever time an injector fires there is a sharp drop in pressure in the fuel rail, the diaphragm in the pulse damper or pressure regulator moves in response, creating a pulse on the other side of the diaphragm to which the sensor is connected.

Inlet manifold vacuum pulse wave forms tend to be much messier and not so sharply defined.

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Originally posted by v8kid
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This project is now on a back burner I tried a couple of other prototypes but I wasn't 100 percent happy with the results. As the puka sensor is now available at a dradtically reduced price so I may actually pay over the counter the money as I can see this might be useful for use fuel rails without a Schrader valve or where the injector electrical connectors are difficult to access.

There is another pressure sensor project on the go --- and it is producing truly excellent results.

[Edited on 14/10/15 by britishtrident]

quote:

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Originally posted by britishtrident
This project is now on a back burner I tried a couple of other prototypes but I wasn't 100 percent happy with the results. As the puka sensor is now available at a dradtically reduced price so I may actually pay over the counter the money as I can see this might be useful for use fuel rails without a Schrader valve or where the injector electrical connectors are difficult to access.

There is another pressure sensor project on the go --- and it is producing truly excellent results.

[Edited on 14/10/15 by britishtrident]

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