You would have to take it to a garage to get a compression and leakdown test.

 

I got my compression tester at autozone for like $30. To have a mechanic do it will cost you at least $100. All you have to do is pull all 8 spark plugs. It is good to have them all out so you can compare them. Start at cyl 1 and record each cylinder reading. I just did mine and 7 of the cylinders were between 190 and 210 psi

For a leakdown test it may cost a little more for the tool but it will still probably be cheaper to buy the tool yourself. It may be worth it for you to buy both just so you know exactly what the readings are and it's not subject to the interpretation of a biased third party who just wants to sell you engine work.

Or you can read the other thread about p3104 and look in to your coils.

 

So I replaced my front o2 sensors and cleared the SES light. It's been close to two weeks now and they have not come back. It seems so far the cylinder 4 misfire is gone. Don't know if this was directly related to the bad o2 sensor but as long as the light is not on I'm happy. The rough idle is gone and my car is running great. Also, before I replaced the sensors I was getting roughly 275-300 miles per tank. I'm now getting 325-350 miles per tank.

 

Thats good news to hear! I replaced both upstream sensors yesterday. No SES light, but they had 98,000 miles on them and surely weren't switching as fast as new ones would. I figured if I could gain 2 MPG, they would pay for themselves in a few months, and from then, they would be like free money. From your figures, my 2 MPG estimate is spot on.

 

Thats good news you two.. I don't have any problems at all (don't worry, i'm knocking on wood right now) after changing out the O2's. They were my main culprit.

Now that the process is done, i'm just waiting to see what pops up next!

Kind Regards to all,