1998 mustang 3.8 diagnois missfire

[stang rider]

1998 mustang 3.8 ltre compression comes and goes on cylinder #5

 

[General karthief]

Stuck valve?

 

[Deleted member 38176]

Your problem is that its a 25 year old V6

 

[Bullitt347]

How did the OP come to the conclusion that the compression "comes and goes"?
What test methods did he employ?
Was it an actual compression gauge? Were the results verified by a second compression gauge to be certain the first gauge was working correctly? Or an observation that #5 cylinder was firing at times, but not at other times?
There are a lot of ways to screw this diagnostic up.