Yesterday my 2000 3.0 Ranger started shaking really badly while idling and accelerating at low speeds. The check engine light came on and I noticed a burning sort of smell from the engine. I took it to O’Reillys to get the engine light tested and they told me I was misfiring on cylinder 6. I told them that I had replaced the spark plugs and wires about 6 months ago so they told me it had to be the coil pack. I bought that and replaced it and it did not solve the problem. I then replaced the spark plug and it seemed to help a little, but now is still just as bad. What else could be causing it?

 

Welcome to the forum

What did #6 spark plug tell you about conditions in #6 cylinder?

Google: spark plug tips images

In my experience a sudden constant misfire is almost always spark plug or spark plug wire.
Coil packs rarely fail, and it would usually effect 2 cylinders with Fords Waste Spark system, there are only 3 coils inside your coil pack, just FYI, each coil sparks 2 separate cylinders at the same time.

The 3 reasons a cylinder fires are:
Spark
Fuel
Compression

Compression is either good or bad, not intermittent, for this reason it is often good to test compression first, and take it off the table so you can look at spark or fuel.
If problem is compression then you can waste alot of time(and money) on non-fixes

Fuel injectors can get plugged or fail, also a rare occurrence unless you have changed fuel pumps or filter lately
Simple test is to unplug the coil pack, 4 wire connector, you want a No Start
Crank COLD engine over a few times
Pull out spark plugs #5 and #6 and compare them, both should be WET with fuel
If #6 is dry then injector is the problem, inspect its wires first, could be bad connector or ???


As for "new" parts.......
New used to mean "tested and working", not any more, labor to test(quality control) costs too much now-a-days
New now means, "you test it and we will replace it if defective"
So don't assume "new" means it works, with any part

Case in point
Motorcraft fuel pump runs $400+, it is tested, required by Ford, and only has 30day warranty
3rd party fuel pumps are $100, not tested, 1 year warranty