Intermittent Misfire With 2010 Prius

Are you second owner, and if so: at what miles did you get it?

A high miles (anything over 150K) 3rd gen, head gasket failure is pretty much a certainty.

 

At some point even though you're the third owner you're going to maybe realize this is not the one. And the one to be throwing money at but maybe it'll take a while. Yep misfire codes are common get your wiper gear out get your plugs out get an inspection camera and get to looking in your spark plug holes that's the first and fastest way to get somewhere in this situation or you can fire parts cannons and just replace stuff and go round and round in circles You can read all about it here plenty of it going on in the last many years You might want to spend more time looking for something better maybe to spend your money on just maybe.

 

The stop-leak product is losing effectiveness, virtually a certainty. Some are flushable, with a 50/50 water/vinegar mix.

First and foremost, you need to deal with the head gasket. Boroscope inspection of the cylinders, preferably with the engine coolant system pressurized, will help diagnose. You're looking for tears of coolant, starting at the head gasket seam, running down the wall. Also, exceptionally clean piston tops, on the compromised cylinders (typically begins on cyl 1 or 2). If the boroscope inspection is done first thing in the morning, you may see a few tablespoons of coolant atop the pistons.

How's the coolant level in the reservoir?

How's the oil consumption?

How's your mechanical aptitude, budget, and how much did the car cost you? This is probably most important; you might just want to sell it, with full disclosure.

If you do keep it, and with the likelyhood that it's got the low tension piston rings and burning a fair bit of oil as well, a rebuilt engine might be best bet. Or get the gasket kit (~$200~250, includes head gasket), new head bolts (~$100?), and for oil consumption: either swap out the piston/rings (low tension rings were used till partway through 2014), or a new short block (~$2K, will have revised pistons/rings)

 

If you do stick with it, be sure to finish up by cleaning the EGR and intake manifold. You may want to replace the EGR components; the cooler will likely be so carbon-clogged that cleaning is impossible, and the EGR valve also clogged, and it’s internals damaged.

^ my 2 cents: it’s the EGR clogging that’s responsible for the head gasket failures. It’s very reliable.

 

Have this. If it's referencing other stuff let me know; I can look.

 

The thing is meter testing is bound to be ok if the car usually runs good. You can do the coil and plug swapping shuffle and determine if the random misfire moves.

However there is a fair amount of work to access them as the entire wiper system and mounting has to be removed. You might leave it off for a day or two while testing the swap.

The only thing I have ever seen that was close to a misfire while a hv battery was low was pre-ignition/pinging from the engine. Pinging due to very low hp contribution from the hv battery. Even then the pinging engine was completely carboned up first due to excessive oil burning.