Check engine light keeps flashing. Diagostic test shows1 misfire condition on 1 cylinder. Changed plugs. Ran good for 10 minutes and now same problem. Running rough, backfiring and cuts off. No power. Spark plugs are extremely oily and one was burned. This is a 2004 Mazda RX8. Have had for about 3 years.

no info generic answer if you have injectors most likely dirty or failing

Do you mean p0303? And on a gm 4.3l V6? If so this is a cylinder 3 misfire. Cylinder 3 is the back drivers side cylinder. You will need to check the plug and wire. A compression test to rule out any I ternary problem would be advisable as well. Compression test needs to be done on all 6 cylinders. The results should fall in a range of +/- 10%. There are tons of causes for this from ignition module, wire, plug, injector or fuel delivery, bad map/maf sensor, valves problem, ring problem etc.

What DTC code(s) are you getting?
You performed a compression test on cylinder #1; did you test cylinder #2?
Compare the readings, if there is a significant difference in compression readings between the two, you may have a bad head gasket, a bad valve, etc.
The bottom line, the problem is internal to the engine.

Time to do a compression and cylinder leakdown test

The SES light flashing means the engine management software has detected a misfire condition resulting in exceeding 3 times the federal limit of emissions. Under heavy load such as acceleration one or more cylinders are misfiring and once cruising speed is reached the engine is under a lighter load (10 to 20 percent ) that is why it stops flashing several causes of misfires are worn spark plugs ,spark plug wires, faulty ignition coil or coils fuel injector or fuel pressure problems a quick check of the computer to retrieve trouble codes should identify the problem cylinder or cylinders and will direct you in the right direction to find the faulty component but will not tell you exactly what is wrong certain test must be performed to isolate the cause.

the spark plugs that you changed, evidently 1 of them was misfiring , according to the computer, and the engine since it was misfiring, made the engine run rich, there fore you said that you changed the o2 sensor, so just make sure that you have the o2 sensor connection is connected good, then take your ob 2 tester, and remove the light, it should go out and stay out, if your tester is not equipped to remove the light, then disconnect the positive battery cable for about 1 minute, then reconnect it, but you will most likely have to reset your vehicles clock, and maybe some radio functions, also if the light comes back on again, check the plug wire that goes to the cylinder of the one that was misfiring, hope that is has helped you.

do a compression test on cylinder 5 & 6 you could have intake leak.and a leaking head gasket or worn valves in those cylinders.

Code P0301
Ignition Coil Pack
Ignition Cable
Spark plug
Clog or dirty fuel injector
Evap canister purge valve
Engine Compression
fuel pressure

you have 3 type of engine for your truck
2.3L 4 cylinder
3.0L 6 Cylinder
4.0L 6 Cylinder

need to know that type Engine

The reason why the service light come on because it is a hard code
not a soft code.

Let me know

do a compression test then do a combustion pressure test if all good computer is questionable

This misfire is most likely due to bad injectors. Check injector pulse with a NOID light. If pulse is good you need new injectors. However before you do all of this get a compression guage and check compression on all cylinders. The numbers shouldn't be more than 10 psi difference in all cylinders for example if cylinder# 1= 160 psi cyl#2=168 that's good but if cylinder#3= 176 and 4=179 there is a problem with 1&2. bad valves or bad head hasket etc. Good luck and thanks for using FIX YA.