2007 grand touring well maintained and got a factory recal lon the timing chain, and so it begins. we took it to a Mazda dealer for the recall. One month prior to this we had an oil change and oil can henry replaced our non synthetic oil with synthetic. After getting the car back from the dealer for the timing chain recall the oil had again been replaced with non synthetic. I was concerned as to the non replacement of the oil filter. Shortly later a check engine light for the o2 sensor came on. Next a loud rattle came from the engine compartment and it was found that the bolts had sheared off and no lock tight had been used. this was repaired and yet again the check engine light for the o2 sensor. I was reassured that it was no problem. The check engine light went out no problem except an occasional rattle was felt on excelleration. 4 months go by a check engine light appears and read a misfire on cylinder 3, (no O2 sensor) we started with replacing the spark plugs. After a few weeks the light came back on, same misfire on #3. Next replaced the coil on #3 we bought from Riellys. After a few days the same light came on, I figured that it could be a bad part so we exchanged for a new one but this time switched #2 and #3, same problem. This time the car started running rough up hill shuttering. We took it to a mechanic, he did the exact same thing that we had done, plugs, coil etc. After he replaced these again he took it for a ride and it ran great for about 15 miles at which point going up hill it lost power lights started flashing and it quit and went into a security mode. Well now the fun begins, it was towed to a mazda dealer to reset the computer, same problem misfire on #3. Mazda dealer said it might be the injector and it will start at 1k to replace, but it is safe to drive. We drove it home less than 7 miles it shuttered and smoked and the exhaust manifold was fire red. We took it back to the original mechanic same thing loss of power couldn't make it up his road, smoking. He replaced the injector, well now the cadillatic converter is fried, he says, but this doesn't answer the shutter which is still going on and it is running rough. another thousand. What is going on? Is the cat convertor going to fix the #3 cylinder misfire? Do both of the O2 sensors need to be relaced on either side of the cat conv? Doesn't make any sense to me.

 

Disconnect the connector from the PCM and check for bent pins. The connector can be problematic if it is not re-installed correctly. Pins can easily be bent.

 

I forgot to mention that you need to put a noid light on number 3 injector connector to see if the PCM is holding the injector open.

 

Where you able to fix the problem?
I had everything just like you mention here happen to my CX7. My mechanic had the Motor heads fixed ($1k) I just got it back from him on Saturday and the engine light came back on, Same code P0303.

 

If memory serves me right, the post O2 sensor would loose it's mind while throttling up and cause the motor to skip a few beats. I cannot remember what code it would trigger if any. If you have made it to the point where the manifold glowed, I fear irreversible damage has been done to the cat.

Not sure as to which bolts sheared off and your whole experience makes me hang my head in shame for the rest of the tech world. The reason the oil filter was not changed is Mazda won't pay for it under the campaign. If the filter was that fresh, it should have been ok not to change.

With all the work that you have had done, it would be difficult and irresponsible to try to play armchair technician at this point. Find one tech, just one, to stick with thru the end to properly repair your vehicle. Personally, as painful as it may be, I would start back at the shop who put this whole mess in motion. Too many hands under the hood wastes time and money.

Would love to hear what the final outcome is, when that time comes.

 

Did you find the cause? I’m having issues with a re occurring p0303 code

 

My guess would be valve guide or rings in cylinder #3 leaking oil which coats the spark plug and causes the misfire. The oil than travels to the O2 sensor and coats that causing it to misread. Then the PCM misreads air fuel ratio and causes the the exhaust manifold to cook causing the decay of the catalytic converter. Also, switching to synthetic oil may have caused some sludge to build up on the VVT solenoid causing restriction of oil to the actuator which would throw the timing, loss of power, chain rattling. In hindsight, reading the oil deposits on the spark plug number #3 would have been the clue. Risk of sludge switching to synthetic might have been avoided using Marvel additive to gently clean carbon and sludge deposits.

 

I think your on the money there, The valves in this car are with the air intake manifold aren’t they? Along that rod? I have them a good clean. Does it cost much or hard job to replace the rings on piston?