Vechicle speed sensor

[Asjad]

(4 cylinder engine toyota)

Dear All,

I recently bought a budget car with no RPM dial.
After looking through a repair manual I found out that there is a
'Vechicle speed sensor' on the engine which connects to the ECU.

I have also found out that the signal from the sensor is available on the diagnostic connector (OBD II).

Would the frequency or duty cycle change?

Since I have no refernce RPM meter How can I relate what frequency I am
getting to how fast the engine is actually running?

(4 cylinder engine)

Any formulas

Regards,

 

[Russlk]

We don't know if the vehicle speed sensor is reading actual RPM or fireings of the cylinders. Assuming that the cylinder fireing is sensed, there will be 4*RPM pulses per minute or 4*RPM/60 pulses per second. If you count pulses for exactly 15 seconds the count will be: 15*4*RPM/60 = RPM!

 

[suicidalmonkey]

Dick Smith Electronics (in Australia, not sure if they ship world wide) has a Digital Tachometer Kit.

See this link for more info: http://www.dse.com.au/cgi-bin/dse.storefront/43f2899104c77bac2741c0a87f9c0789/Product/View/K3241

 

[Nigel Goodwin]

Dick Smith Electronics (in Australia, not sure if they ship world wide) has a Digital Tachometer Kit.

Yes they do! - and very quickly as well!.

 

[stevez]

The output of the OBDII connector is data. There are a number of instruments available that look into the ECU via the OBDII connector and will give you a real time look at all sorts of things including engine RPM. Many of them requrie a laptop and are more for short term use in tuning or diagnosing a problem. I'd expect some to be built for continuous monitoring or logging of data.

 

[DirtyLude]

VSS is always based off of the final drive, it's never off of the engine. The Vehicle Speed Sensor is for the Speed gauge, not the RPM gauge, so if you are looking to use this for RPM sensing, it's not going to work.

If you actually want a RPM gauge, guaranteed there is an RPM reading going to the ECU, you just have to look for it. There are several aftermarket tachometers available from places like summitracing.com or restoration retailers. It's easiest just to get one of these. They will have ways to select the division factor for different #'s of cylinders.

There's some really simple cheap ones that are just LED line displays, if you don't want to get too fancy.