when don said short, this made me think of something. is it possible you might have pinched a few wires, or melted some wires on the exhaust? there was a problem in some ranger years before you (i had a 91 that this happen to) that the harness was too close to the drivers side harness if i remember correctly that melted a couple of wires, and shorted out the computer. when that one happen it shorted the fuel pump wires and the pump wouldn't turn on. completely different problem that your having, but it might be something to look at.