Is it worth it to be cheap and only change injectors as needed. Or just bite the bullet and do all at once
Do you have one going down? To me it all depends on mileage and if you're working on your own stuff.
To a customer I suggest replacing at least 4 at a time. That way you won't have to have that valve cover back off to replace injectors. But if you have one injector on each side that's bad then I would suggest doing them all. I usually tell people if one is bad the others probably aren't far behind.
Now if it's mine and I'm not paying the labor bill then I would replace the bad ones....maybe....depending on mileage though.
If you can swing it just replace them all.