2010 Prius engine misfire intermittently

I have all the same issues and the same exact experiences. Came on here looking for answers also.

 

welcome!
how many miles on her?

have you cleaned the egr circuit?

might be a coil as well.

 

First off, some here suggests you need to clean the EGR system end to end if you read enough posts here in PriusChat and I totally agree with that. This means cleaning the EGR cooler, EGR valve, passage pipe, and the intake manifold.

You mentioned car was in motion, was the engine misfiring under light load or partial throttle cruising speed? Cause can be:
1) a clogged EGR system. The EGR system is to bring in exhaust gas (inert gas) to cool down the lean burning condition of partial/light throttle to reduce NOx. If the EGR system is clogged or the EGR valve is stuck closed due to carbon buildup, without exhaust gas presence when the system expects them there, you may have pre-ignition, pinging, misfires etc
2) carbon buildup in combustion chambers, like piston top, intake valves, fuel injectors. These can cause incomplete burns and misfiring, increased compression ratio etc. Do you use high quality gas?
3) @bisco mentioned, bad ignition coil? Properly measuring the coils to make sure they are within specs and in working conditions before throwing money into parts.

Anyone wants to add reason # 4, 5, and etc?

 

I think you got it covered.

And not covered in carbon buildup either .

We’ll save that for the next meetup with the pressure washer.

 

I'll be pressure washing my house in the next week or two so I'll get a chance to test it out
on my spare egr cooler after filling it with oven cleaner!

 

Save the oven cleaner and see how easy it is.

 

Well, I thought about doing that. But if it doesn't clean it good enough. I'll have to let it dry,
then use the oven cleaner.
Maybe I'll do it before I start the house. So if it doesn't do so well, it will have time to dry in the sun.
Then I can clean again after cleaning the house...
I have a bore scope and figured out how to use the LIGHT.... So I'll try to remember to take
before and after photos...

 

Ray I do think my Prius has more carbon buildups than I would hope to see, one of these days I will open up the EGR pipe to take a look.

Before, quite often my 9 mile commute is in stop and go traffic with incomplete warm ups (lack of Italian tuneups LOL). Leaving office to go off site is also in traffic although it becomes a 16 mile slow and go traffic. Nowadays I have to drive in high/full throttle up hills that may blow oil through PCV valve and into my oil catch can (too much of that Italian flavor now).

Please keep us updated with anything your mechanic finds and suggests. Definitely something is there as the misfiring and engine light keeps coming back.

 

The only issue i've experienced with a clogged EGR is "pinging" (rattling sound) under light acceleration; never any sort of mis-fire that would cause vibration (only had that with bad spark plugs or vacuum leak).

Just a humble guess but I've heard that a bad ignition coil could cause intermittent misfiring issues like this? Maybe one of the coils is developing a short-circuit and randomly fails to produce high voltage sometimes?

 

Did he clean the EGR COOLER??????
That is what really clogs. Then you'll get excess back pressure causing the head gasket to blow.
Did he check for a leaking head gasket too?

 

You're cherry-picking what answers appeal to you, lol. You need to clean the full EGR circuit and intake manifold, asap. And test for head gasket already failing, leak-down test and check the coolant for carbon monoxide.

Or just keep driving till the head gasket blows, and/or a piston arm is bent. Then your "local mechanic" can put in a new engine.

 

maybe a coil can work intermittently? idk

 

MMM, did anyone mention cleaning the COOOLLERRR???