You described the problem perfectly. Do that in words, or show your mechanic this post.
The only thing I can add is about the temperature gauge. A lot of people don't even pay attention to it until it's too late. The coolant temperature sensor for the dash gauge is a little ways away from the thermostat. As the engine warms up, the heat in the coolant has to migrate over to the thermostat to cause it to open and let coolant flow through it. By the time that happens, that higher temperature has already been detected by the sensor so the gauge reads a higher temperature. Once the thermostat opens, cold coolant in the radiator rushes into the engine and up to the sensor and thermostat. In response, the dash gauge goes down and the thermostat closes. The whole process repeats again. That suddenly started happening after about 15 years on my '88 Grand Caravan after nothing was done to it. The gauge would go up and down wildly four or five times before it would settle down.
The fix for that is to drill a tiny 1/16" hole in the plate in the thermostat, then reinstall it. That will allow a little trickle of coolant to flow all the time so the hotter coolant can reach the thermostat sooner. That hole is way too small to affect the operation of the thermostat in any other way. Most import engines have the same problem and you'll find their thermostats already have that hole and a little "dingle dangle" hanging from it.
As for the misfire, the spark plugs and wires are the most likely suspects, but don't overlook the ignition coil. Ford has plenty of problems with them. If they start to arc internally, that can happen when just one cylinder is firing if that spark plug needs more voltage than the coil can deliver before it arcs internally instead. (Electricity takes the path of least resistance). The symptoms should change when the new spark plugs are installed because the new plugs will take more or less voltage than the old ones just because their gaps are different.
Ford also has a real common problem with their EGR systems on their full-size trucks. I don't know if this can happen on a Ranger. The tube carrying the exhaust gas to one cylinder gets plugged with carbon so that cylinder only gets fresh air and gas, and it works fine. All the exhaust gas is split among the remaining cylinders, five in this case, assuming, again, this applies to your truck. Those five cylinders still get enough fresh air and gas to run okay. Pretty soon a second tube gets plugged, then a third one. The volume of exhaust gas is what's controlled, and the engineers just assumed it would be split evenly among all the cylinders. Eventually all but one tube is plugged, and since the overall EGR volume is staying constant, it all goes into that one cylinder. To say it a different way, that one cylinder gets six times as much exhaust gas as it's supposed to. That is the only cylinder that is working right, but it's the one that will misfire because all it has is spent exhaust. It doesn't get any fresh air to go with the fuel.
There are a lot of fault codes related to the EGR system and they mean different things. If your code refers to volume or "insufficient flow", check for carbon plugging the tubes.
Tuesday, October 14th, 2014 AT 10:27 PM