2010 @120k miles. Misfiring after spark plug replacement and sulfur smell?

Yeah sulphur/brimstone smell is always alarming... Not sure, I've heard this before, just not enough brain cells to recall what that was due to. Maybe the Catalytic Converter??

Knocking and codes regarding cylinder misfire, in particular #1 and #2, often end up being failing head gasket. Try swapping the coils around first: swap coil #2 and #4, see if the code changes to P0304.

If it doesn't:

1. Check the coolant level, is it stable, or requiring frequent top-up?
2. Boroscope inspect the cylinders, looking for coolant in cylinder 1 or 2 in particular, and/or they look particularly clean, compared to the rest.
3. Do a leak-down test.

Have you ever cleaned the intake manifold or Exhaust Gas Recirculation components?

 

Welcome to PriusChat.

Was there a misfire code before you changed the plugs? What plug did you install?

If you have looked around here, there's an issue with the EGR system clogging in the Gen-3 Prius. One manifestation of a clogged EGR, for some, has been a misfire code, caused by a leaky head gasket.

Others will chime in but I'd suggest moving the #2 igniter to see if the misfire moves with it. If so, it's the igniter. If not, go on to the EGR system, and consider an inspection of the head gasket (scoping or leak-down test). Related: has your coolant and oil level been constant?

 

Just googling the sulphur smell: one reason is the cat, another is an engine running hot. Clogged EGR will elevate engine temp.

 

Though no one around here, it still must be pointed out, has ever ballparked the question "by how much?", or even how many digits might be in the number.

 

If there's a misfire then the cat is not working well. That alone should be enough to get hydrogen sulfide.

So far it sounds a lot like the classic high miles prius with gummed up oil rings & clogged EGR, gone to end stage. Don't panic though- confirm these elements and see if you can save it.

 

Sounds like gummed up,think I would start here with a clean, also fo a piston soak and engine flush to help with oil burning problems

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Egr gummed up

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Try old plugs back on, maybe new plugs are counterfeit

 

With misfire persisting on cylinder 2, regardless of the swaps, sounds like head gasket. Try leak down test maybe next.

 

Here's some videos. These guys go through at break-neck speed, cut corners I suspect. But worth a watch.

New head gasket replacement video from Gasket Masters | PriusChat

 

I'd be cautious. HG failure is a common event on these cars at higher mileage, and maybe it has become an overly common diagnosis. I don't think of 120k miles as being very high for these cars, and for report of HG issues.

At the very least, I would try to get direct measurements (compression test, leakdown test, block test) before diving in. Any coolant issues?

Clear liquid coming out of your exhaust upon startup can be a completely normal thing that happens when the condensed water vapor is expelled. Do you have any humidity down there in Texas? I assume you are running pink / red / green coolant rather than pure water as coolant, right?

I'd be very concerned about any spark plugs you put in there being fake.

Some "scorching" around the ceramic on the spark plugs that were in there may be normal, or at least not a critical problem.

 

Yeah I was thinking he's done leak-down test, maybe not. Just "all signs"?

 

If leakdown test says pressure is within normal specs then buy non counterfeit oem plugs. Do a search here and you’ll be amazed how many victims it claimed because they wanted the cheapest of the cheapest purchased price.

 

It's not always the price. You'd be surprised how many autoparts get mail ordered specifically to avoid having to talk to the weird guy at the counter in the store. And that was before covid.

 

I knew I forgot something

Disclaimer- this reply may not apply in all situations.