If the zerk fitting is new;
Pull it out and see what is at the bottom of it. It should be soft grease. If it is anything hard, 1) try and clean it out with a pick and see if it will take grease. If still no joy 2) replace the joint.
If there is any chance of the joint being salvageable, there will be a point in the travel or suspension extension that it will accept grease. If no matter which way you move it, no grease will go in, the joint is smoked. Either plugged solid, or the grease valley is mangled. Either way it is a ticking time bomb.
If this is a tie rod end, you are risking a catastrophic failure. When it finally goes, there will be no warning. The ball will fall out of the fitting and both tires will steer in different directions. It depends how fast you are going if the damage to the front end will be repairable. If you are lucky you will be able to jack it up, put the joint back together with bale wire and get it home. If you are not lucky, well….. even if a joint is tight when you shake it, I wouldn’t trust it if I haven’t been able to get grease in it for 4 years.