Technical Cam Sensor and Crank Sensor - Sensor Type?

[conors891]

Hi all, I have a mk2 punto 8v. I am making a DIY tachometer. I have it working off the trigger to the coil pack but the result is laggy and inaccurate. I am now hoping to get a signal off either the cam sensor or the crack sensor. Does anyone know what type of sensors they are, and what kind of signals they produce? Thanks, Conor

 

[judderbar]

Hi all, I have a mk2 punto 8v. I am making a DIY tachometer. I have it working off the trigger to the coil pack but the result is laggy and inaccurate. I am now hoping to get a signal off either the cam sensor or the crack sensor. Does anyone know what type of sensors they are, and what kind of signals they produce? Thanks, Conor

If you have a two wire sensor coming from your crank sensor it produces a very good square wave by following the shape of the notched crankshaft wheel. You can drive an LED off that signal to test your sensor. The two wire sensors are just a a coil of wire wrapped around a magnet.

https://www.fiatforum.com/punto-ii/429490-testing-crankshaft-sensor-ecu.html

 

[conors891]

It's actually a 3 wire sensor. Red, black, and white. Presumably Vcc, GND, and signal.

 

[Ziggy122]

So u wanna have a rev counter.... basically?

Fit an up spec dash instead?

Ziggy

 

[conors891]

Thanks for the response Ziggy. Not looking to replace my current dash. What I have is an arduino (DIY programmable computer) and a small LCD screen. It displays the revs on the LCD. The arduino likes a nice clean 5v signal to work properly.
So I need to work out what kind of signal the crank sensor produces (I don't have an oscilloscope to check for myself). It would be ideal if it was a 5v square wave which, I believe, is what hall effect sensors produce, if it is a hall effect sensor. Thanks

 

[Ziggy122]

Never really looked at the waveforms on them tbh....

But the phlonic wheel where the crank gets its signal isnt stepped toothed its got a curve on them
Something tells me it wont be a square waveform but more of an ac waveform
With the flattened notch to dictate tdc

Ziggy

 

[conors891]

On a separate note, when the ECU detects it's at tdc from the crank sensor how does the ECU know that cylinder 1 is at the top of its intake stroke rather then power stroke?

 

[Ziggy122]

On a separate note, when the ECU detects it's at tdc from the crank sensor how does the ECU know that cylinder 1 is at the top of its intake stroke rather then power stroke?

Cam ans crank correlation
The cam shaft has a sensor lobe on it
When crank tdc is picked up
It uses the cam to tell whicj cylinder

Bearing in mind ths punto uses waste spark system, so regardless if no1 is on exhaust it still gets a spark cause no4 is tdc

Ziggy

 

[conors891]

3 wires coming from crank sensor, red, white and black. Measured from a DC multimeter, when the engine is on, red is at 1.44 V, white is at 2.05 V and black is ground. The 2.05 does not change at all with RPM. Really need to invest in an oscilloscope to figure out what's actually going on.

What kind of singal do the fuel injectors get? Would I be able to get an RPM signal from it?

Thanks, Conor

 

[g8rpi]

Hi Connor,
Normally the 3 wire sensors are hall effect type with a 5V supply. Not too sure why you are only seeing 2.05V supply, but it sounds like there may be a ground issue. Where are you connecting the meter common?

Robert G8RPI.

 

[conors891]

Thanks for the reply. Yes I expected 5v too. Perhaps not a hall effect sensor? I tried with the meter common connected to the negative of battery​ and black wire to sensor. Got the same result in both cases