89 ford ranger check engine light blinks when I go above 55mph. Is there a common problem with these trucks that I can diagnose myself?

If the engine light is blinking then u have a dead miss, could be as simple as a spark plug or wire, but I've seen several coil packs go out on just one cylinder and usually under a load.. Code will be p030? Whatever number is listed at the end is the problem cylinder, if it was p0304, that means cylinder #4 is the problem. Hope this helps.

Go to a local Napa, or Shucks automotive store and ask for the computer to plug into your vehicle and have it give you codes. Take those codes to the employee at which ever automotive store you went to and he'll tell you what issues you have.