How to turn on/off particle system?

hi,

I'm making engine. and it's constantly working. ( on/off every time)

so I use this code,

     public void engineEffect(float up, float forward, float right)
     {
         var emissionUp = upParticle[0].emission;
         var emissionDown = upParticle[1].emission;
         if (up > 0)
         {
             
             emissionUp.enabled = true;
             emissionDown.enabled = false;
             
         }
         if (up < -0)
         {
             emissionUp.enabled = false;
             emissionDown.enabled = true;
             
         }

     }

that up value change it's value -1 to 1 I need to enable those particles. but it don't work. it's enabled the emission. but I can't see my particles.