2011 Gen 3 Prius Misfire

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And misfire is back. P0303 all over again. I checked the oil and it was bone dry so changed the oil and pulled the plug. Plug was fouled up real good. So I put in a new plug, used mobil1 HM 0w20, and cleared the code. Drove it for a few miles yesterday and thought so far so good. Wife goes to take the kiddo to school today and the code popped again. It almost looks like oil is getting in the area where the spark plug electrode is. The threads are all bone dry right up to the electrode.





Any ideas?
 
Oil in the cylinder -- rings, valve seals.

Are the valves adjustable? Valve that is too tight will cause misfiring.

I would suggest a compression test though that may be complicated to do on a hybrid car.
 
We had a compression test done about 2 months ago and they said compression looked great on all cylinders. I'm not sure if they are adjustable on this car or not. Code came back this morning but car is running fine. I'm going to clear it again and see if this was due to some oil still in the cylinder that burned off. I'm hoping the high mileage oil can buy us some time at least.
 
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Also if it is the ring on that cylinder would that make it a good candidate for a few short oci's? I'm afraid to use something like MMO in the oil since it's already using 0W20. It's pretty thin as is. Or would you recommend a piston soak? If so what would you recommend and how long?
 
If I remember right, compression test only checks the ring and not the valve stem seal. Can your mechanics check that and see how it goes?
 
Originally Posted By: Rtstrider
... I'm hoping the high mileage oil can buy us some time at least.
Not likely, when the problem is coked #3 ring grooves and drain holes, unfortunately a common problem on this engine and certain older Toyotas.

What kind of oil has been used in the engine most often, and how often have you had it changed?
 
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