WRX V11 - Sensor input wiring help

[R4CER]

Hey link community, hope you're all good. 

Had a couple quick points I was hoping you could all validate/help with (or tell me im barking up the wrong tree with). 

I have oil pressure/temp gauges in my car (2015 UK STI), and was looking to splice in these to the link for monitoring/logging etc.

My car is no longer running the MAF, so I have that wiring available to me for use. Am I correct in thinking that I can use:

Pin 4 in the diagram below (at the factory plug in the engine bay) to splice wire in my oil temp sensor (if I go to the plug, do I need to flip the jumper on the board?). Would I need to also splice in the ground to pin 5?

Pin 3 as above, to splice in my oil pressure sensor signal wire, with it being a signal wire, I pressure I wouldn't need to feed/ground it as its currently being supplied by the gauge here but please do correct me if im wrong.

And finally, I'd like to get fuel pressure wired up for monitoring (given ive just had a fuel pump go bad, so would be nice to monitor that moving forward). 

I currently have expansion 1 plugged in ran to the bay.

I have flex fuel running on DI11, IAT on temp 4 (grounded back on the expansion) leaving Inj5/6 Knock2 and Aux16 free on this expansion. Am I right in thinking that none of these can be used to take a pressure signal input and that I would need to look for another volt input? Im not running a rear 02 sensor, so I could run this to the factory wiring on AN volt 7 (rear o2 signal) if my thinking is correct? Assuming this won't cause any issues doing it this way.

Thanks in advance for the help, 

-Alex

 

[Vaughan]

Temperature sensors typically work by having a resistance that changes with temperature, to read the resistance value you apply a pullup of know resistance to a known voltage and then you can read the voltage between the pullup and the sensor and calculate the resistance of the sensor in the same way a resistor divider works. This means that if you have a temperature sensor connected to a gauge that gauge has it's own pullup to a certain voltage inside of it, if you then connect another pullup to that sensor (which happens when you connect An Temp 3) then the reading for both the gauge and your EC signal are now wrong.

You can read the resistance of a temperature sensor that is connected to a gauge by using either an An Temp with the pullup turned off (An Temp 1 or 2) or an An Volt input but you will need to determine the pullup resistor value the gauge is using, the voltage it is pulling up to (if it's more than 5v the ECU inputs may not have enough voltage range) and you also need to determine the resistance to temperature calibration of the sensor itself.

 

In terms of oil pressure if it is a 3 wire sensor with 5v to one of those 3 pins then you can connect an An Volt directly to the pressure signal pin and you only require the calibration data for the sensor.

If the Pressure sensor is a single wire sensor then it is the same issue as the temperature sensor where it is a resistance that varies with pressure that is connected to ground and then has a pullup applied to it, if that pullup is 12V the An Volt won't have enough range and you also need to know the pullup resistance etc.

 

My solution for this would be to fit a Bosch combined pressure Temperature sensor, wire it to the ECU and then if you want the gauges to work if they are both single wire sensors then you can just use two PWM capable Aux's to control the gauges based on the values the ECU sees.

[R4CER]

Thanks @Vaughan, super useful reply as always. certainly some food for thought. Perhaps I should just do away with my analog gauges and go for a link can gauge in its place 🤣.

Are my thoughts above correct re the fuel pressure sensor, i.e. if I was to run the link pressure sensor I could then feed this into AN Volt 7?

Thanks,

Alex

[Confused]

I would 100% remove the dumb gauges - sell them on to someone who is still stuck in the 1990s, and wire sensors directly to the ECU.

The ECU can then deal with the data from these sensors directly, and you can replace a sea of gauges you don't actually look at when pressing on with a CAN gauge, which can show you the information you need generally day-to-day, and flash up any warnings etc when things go out of spec - that's if the ECU hasn't already started to react and deal with it!

[Vaughan]

11 hours ago, R4CER said:

Are my thoughts above correct re the fuel pressure sensor, i.e. if I was to run the link pressure sensor I could then feed this into AN Volt 7?

 

Yes you can absolutely run a fuel pressure sensor signal into An Volt 7 on the O2 sensor plug, probably use the 5v and ground from something like your TPS or MAP plug for the other 2 wires.