95 mercury mystique, 91,000 miles, v6 engine will start and chug away on what sounds like two cylinders. The " trouble codes are 214 & 543. The fuel pump is fine and puts out the correct pressure. I have replaced the cam sensor, the coil pack & the ignition module to no avail. What's next, dynomite?
The crankshaft sensor is the one that drives the ignition system. Usually the camshaft sensor drives the fuel injector timing. It almost sounds like the timing is off. I wonder if the timing chain has jumped a tooth.
The problem with your discription, it sounds like it could be fuel, ignition, and timing.
Fuel system is very simple, comes from pump to filter, then to fuwl manifold and sits on the injectors waiting for the PCM to control the injectors based on the cam shaft signal. Fuel is also ported off of the manifold to the regulator and then back to the tank. When you test the pressure, you must use a " T" fitting so the regulator can be tested also. This pressure should be regulated at 35-45 psi. Too low or too high will cause issues.
Ignition is simple also. The PCM sends a signalt to the Ignition control module. This ICM looks at the crankshaft sensor for a timing pattern to fire the coil packs. The ICM and the PCM talk back and forsth to determine the timing and sequence for a spark signal to the coil packs.
This leaves timing. If you have exhausted all other tests, and the engine still is running this bad, you may want to remove the timing cover and make sure the timing is still correct on the crank and cam shafts. In the old days you could loosen the distributor and rotate it to make it run better. Then you would know. But now it is a little harder.
A compression check on the engine may be a good trouble shooting test also.
Im sorry I cant be of more help.