engine missfire codes for #1,2,and 3 cylinders

What is your question?

I have the check engine light on and have an engine miss. At about 2000 rpm's the check engine light begins to flash. I hauled the car to the local dealer and paid them to troubleshoot and give an estimate. I was told that it was the ecm and would cost me $1800 to replace. I then asked them if they would guarentee that this would fix the problem and they said they could not. They said there were misfire codes for the whole pass side #'s 1,2,and3 cylinders. they swapped around the plugwires and still no change. I have changed the plugs with new ones after i brought car home after not letting them throw parts at it to fix try to fix it, with no change to engine performance. I know there is a timing chain tensioner in each head that could cause a misfire on one whole bank. Is there an easy way to check this? what is the possibility of having bad coils for #1,2,and 3 cylinders? How would a guy isolate the problem?