Car jump script not working.

if (Input.GetButton(“Jump”))
power += forceToAdd *Time.deltaTime;
Debug.Log (“Jump”);

	rigidbody.AddRelativeForce(Vector3.up * power);
	Debug.Log ("Not Jumping");

Any idea why this isn’t working? This is in the function FixedUpdate.
It’s to make a car jump upwards when the space bar is held down and then released (to add power the longer you hold it).
It seems like it should work to me… the debug logs come up as expected so i know it’s recognising the function.
The car is controlled with forces by the way.
thanks for looking!
oops forgot to say, there are two vars for this;
var power = 0.0;
var forceToAdd = 5.0;

Firstly I noticed that the ‘power’ var was going up by 0.1 for every button press (down and release) so i changed the code to Getbutton instead of GetButtonDown and it started to build up the value.
However my var forceToAdd seemed to have no impact on the result, it wasn’t applying 5 per step as i thought it should so I removed that var and just replaced it with a number in the function.
Then I realised I needed a much much much bigger force to see any result so i took it from 5 to 5000000 and it works well enough.