MK2 false values when input disconnected - Needs FIX!

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MK2 false values when input disconnected - Needs FIX!

Post by limai »

While troubleshooting a fuel pressure sensor, I found that the readings displayed form the app, not sure if it is app only or MK2 problem as well, are not real.

Before starting engine, Oil Pressure sensor reads "0" on app, start engine pressure increases and decreases to the idle pressure.
If the sensor is input is disconnected from the MK2 the pressure display does not go to "0" it displays the same value displayed before disconnecting and the value is fluctuating as if the value is LIVE.

This is a huge problem when I am using the app as a cluster and it should be a must that the system can recognize when the sensor is disconnected. As is I cannot trust the value is real or the actual pressure.

Video of display while disconnecting sensor input.

Please advise, I cannot use or trust the MK2 until this is resolved.


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Post by brentp »

Hi -

Sorry for the late reply.

RaceCapture has very high impedance buffered inputs which allows you to connect to existing sensors on the engine without dragging down or affecting those inputs.

It's like an instrument - think of it like a digital volt meter, where you measure the voltage of the circuit and you expect that the measurement won't affect the circuit.

As a result, the inputs are very sensitive and will show a reading for a period of time until the charge on the input decays. The charge will decay, but will take some time. For example, if a full 5v is applied to the input, it will take about 1 minute for it to decay to 1v.

If you want it to decay faster, you can add a pull-down resistor to those inputs. Use a very large resistance value to prevent your sensor reading from being affected.

You can try using a 1 meg ohm 1/4 watt resistor between the terminal input and ground. These will work: ... 1%2F4+watt

Connect it like this:

Code: Select all

RCP Analog input  ------------1 Meg ohm RESISTOR ------ Ground
                      Your sensor

Overall, it's important to remember that RaceCapture/Pro cannot detect:

1) A failed sensor - a failed sensor can fail in a variety of ways - it can fail with:

* a stuck voltage output (showing a constant voltage on RaceCapture)
* it can fail to full range (showing maximum value on RaceCapture)
* it can fail to zero (showing zero value on RaceCapture)
* or it can fail with random value outputs (showing fluctuating, random values on RaceCapture)

2) Wire faults - wire faults can be: broken circuit, accidentally shorted to ground, and accidentally shorted to voltage - with similar effects as 1) above.

So - it's really important to use good quality sensors, have properly connected wires that are protected in bundles from heat and abrasion.

If you are very concerned about ensuring a sensor reading, you will want redundant sensors, and ensure that both sensors are always in agreement. This is how military, aircraft, space and other high reliability environments do it.

Hope this helps, and sorry for the confusion!
Brent Picasso
CEO and Founder, Autosport Labs
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