Technical RPM signal wire?

[MarkFreddy]

Hi Guys!

I am looking for the RPM signal wire, Grande Punto T-Jet (2008). I like tinkering and wanted to try and make a neat shift light. But I need the RPM tachometer signal.

Anyone knows how to find it, or even better; where it is?

Thank you !

 

[J4MALD1N]

I've checked online and cannot find any exact guide on a Grande Punto. However, you can source down the wire. In my own words I may confuse you so below is a more elaborate guide on finding the signal wire. It does require you to probe pins on either the ECU or binnacle connector. There are a range of guides available on YouTube to help you find that wire.

To properly test a tachometer wire in a vehicle will require a Digital Multi Meter capable of measuring AC voltage. Note that a typical tachometer signal is not true AC voltage but pulsed, DC voltage. A Digital Multi Meter is not fast enough to read the pulsed DC voltage and this is why you need to use the AC voltage setting. Set the meter to AC voltage. Connect the negative Meter lead to a good chassis ground in the vehicle and the positive lead to the suspected tachometer wire. Start the vehicle and wait for it to idle down to normal idle speed. At this point the meter should be displaying a fairly constant AC voltage. If this is the case, rev the motor up and down and observe the reading on the meter. The AC voltage should rise when the engine RPM’s rise and fall when the engine RPM’s fall. Locate a tach source that has at least 3V AC at or slightly about idle speed. NOTE: DO NOT USE any other method to test a tachometer wire such as a test light, this can cases damage the vehicle!

All the best!

 

[GrandePunto PL]

I doubt that there is literally "RPM signal" anywhere (electrically, not as OBD2/CAN data frame - that's another option, doable at home), despite some manuals/schematics calling it that (it's rather colloquial name, not 100% scientific). It is not pure, literal, processed, distilled "RPM" per se.

But there are crankshaft and camshaft sensors, connected to the ECU (and for example "eLearn" has schematics) - I thought that's obvious(?) to the DIY guy attempting such project.

If you want to do some DIY electronics, you must be able to grab that "signals" (and not disturb them and fry the ECU), "condition" them (levels - some sensors are ground referenced, some are not, "floating"). Crankshaft "phonic wheel" has many teeth, you must handle it somehow in your project (count the number of all pulses and deduct what is the RPM or "just" detect the longer ones - ones that correspond to the "missing" teeth).

 

[MarkFreddy]

Thanks! Found a signal corresponding to the rpm's your way @J4M4LD1N.
Though I'm not sure if I should tap that straight from the ECU.
A canbus solution seems safer, just have to figure out how to retrieve the signal that I want.
I've seen someone using a bluetooth OBD dongle, but I don't like this solution due to latency in BT connections,
Thanks for the help guys, I think I can figure it out from here

Martijn