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Measuring Fuel Pressure on Mazda RX7s with Modular ECUs

April 08, 2018

 

I’ve explained in other articles the benefits to measuring fuel pressure; firstly it allows you to monitor the health of your fuel system but more importantly it allows the ECU to know the fuel pressure seen by the injectors, and therefore how long the injection pulse needs to be to deliver a given volume of fuel. So we highly recommend adding a fuel pressure sensor when installing an ECU.

 

 

Most modified RX7s tend to convert to at least the secondary injectors to top-feed style to increase the flow. Because the factory fuel pressure regulator is mounted on the secondary rail, this means that normally an aftermarket fuel pressure regulator is added.
This provides a convenient place to connect a fuel pressure sensor; because almost all aftermarket regulators have a 1/8 NPT fitting into which you can screw a gauge. So it’s very simple to screw a pressure sensor into that location instead. The sensors we sell are 0-150 PSI gauge pressure; you can use other sensors but you must ensure they are rated for fuel use.

 

Once you’ve mounted the fuel pressure sensor and checked for leaks, you can wire it in. There are two ways to do this if you’re using a plug and play ECU. The first is to wire it into the dedicated fuel pressure input pin on the ECU. Cut the wire that goes out to the loom, and connect the signal output of the sensor to this pin. Then Tee the 5 Volt and sensor ground connections to those that go to the TPS, MOP sensor and so on. You can find these pins on the diagram in the software.

 

 

The alternate method is to wire the fuel pressure sensor into the factory MAP sensor wires, and use the internal MAP sensor in the ECU to measure manifold pressure. If you do this, you’ll need to select the (d) source for the fuel pressure as coming from the external IMAP (intake manifold absolute pressure) input.

 

change the source and sensor type go to (a)” Input” tab in Home Ribbon, then (b) select “Fuel Pressure Sensor”.

You’ll also need to (c) select the sensor type – 0 – 150 PSI gauge being the most common, and once you’re satisfied it’s reading correctly, Select the fuel pressure as being “measured” as opposed to “nominal” in the software, and the ECU will automatically take the fuel pressure into account when calculating the injector pulsewidth.

 

change fuel pressure modeling, go to (a) “Output” tab in Home Ribbon, then (b) select “Fuel System”

 

Thank you and happy learning!


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