what could be the reason i hear a tickin noise only under acceleration. i thought it was an exhaust leak but wouldnt i always hear the noise. the truck is a 89 5.0L

 

could still be an exhaust leak even only under accel., but if not, sounds like it could be lifters.

 

Any chance it is detonation? Detonation doesn't sound like a ticking to me but since you mentioned it only does it under acceleration and it is an older engine.......

If you are not sure if this is it, fill her up with premium and see what happens.

 

premium does nothing i use to put it in every time at the gas satation until it wet over 4.20$