The only way to be sure is to do a compression test. Pull the coil wire off, pull the spark plugs and tesh the compression with a gauge. All of the cylinders should read withing a small % of eachother.
oil consumption......could and i stress could.....be one tell tale sign put your thumb over your breather if it can blow your thumb off you have blow-by which is caused by worn out rings.
What symptoms are you experiencing? A compression test it a good way to determine general mechanical health of compression rings. You can get a guage for around $20 and follow the instructions that come with it. A vacuum guage is another tool that gives you an idea of general health, you have to be careful though because aftermaket cams and such reduce vacuum and that is normal. And lastly you have the leakdown test that can help narrow things down if the other tests indicate problems. I have not done a leak down, I would follow the directions that come with the kit. These tests are designed to eliminate mechanical problems as the culprit before chasing wires and sensors. No use in pulling codes and such if the engine has mechanical problems.