My 1984 is having some engine trouble but Idont know what it is. I had my car diognosed three times and they cant find the problem although they said it may be the spark plugs, they changed them and put new ones they also did other stuff to it but it still loses power and has misfires this is after driving the car for thirty minutes but before that it runs great. What can be the problem and how can I fix it?

 

Have you checked fuel pressure? Any codes? Could be the ignition coil also.