I broke down 3 miles from home :(

Hi Mendel,

Thanks for being frank. Yes, I think it was a mistake to get home in that state. I thought about it all day today and regretted what I did. There was absolutely not a slight possibility of an engine damage if I had stopped and looked for a tow.
And this is even worse that I then remembered (the next day) that I had a towing package on my policy up to 5 miles. I could have used that. Sure it would have been a few hours of wait maybe but it would have been well worth it.

Now many of the members here are betting on a defective plug. That could very well be it. It might be just a plug but if I damaged that engine, what good would that be?
I read the AESC article posted by ChapmanF. It states that even though a plug may look okay, they might be bad.
Well, the only way to find out is to replace them with OEM ones.

 

Thank you for this Chapman. I will save it to my Pirus folder.
It makes me think the slight burned smell I got when I arrived home might have been from the Cat. The poor thing gulped up unburned fuel throughout the journey back home.

 

Hi guys,

First off, I apologize for not providing any update for weeks. If you read my story from the beginning, this happened to me less than 2 days before my trip at a super busy time. I left the town about 40 hours after the incident. I had to take care of many things before my trip that I couldn't make time to work on my car.
Many of you provided valuable comments. After reading your comments, my goal was to at least pull the plugs (at least the #2 plug) out and post a picture prior to my departure. And I was sure I could have time to do that. I unfortunately didn't. Pulling a spark plug from any car would probably be possible in 10 minutes or under; however, when we are talking about Prius, we know this isn't the case.
I had about 45 minutes of time to spare before heading to airport on my last day and thought about making one last effort to pull the #2 plug out. However, my car was in the garage which was 95+ degrees F (Florida heat and humidity for those who know); I just couldn't convince myself to have that last minute battle. And I left.
5 weeks later, I got back to town and pulled those spark plugs out. When I was out of town, I kept thinking if it was going to be as simple as a spark plug related issue. And I was hoping to find a badly damaged plug and be happy. However, it isn't quite like that per what I see. I have the plugs in my hands, and I will be posting the pictures shortly. You will also see the original plugs (I still have them) to compare. Original plugs stayed in the vehicle for about 8-9 years and had 150k miles on them.
The ones I replaced (purchased from ebay) installed in 2018 and had only about 50k miles.
Both set look pretty much the same to me, but I will post them for your comments.

 

By looking at the spark plugs, I don't see an immediate red flag; however, I have had spark plugs looking perfectly fine but not working. So, it could still be the spark plug issue. (I hope )
I checked the coils visibly and didn't see anything obvious. Of course, it could be a defective coil. And when they go, they often don't show any sign.

I have an inspection camera, but it is not small enough to go inside the cylinders. I won't be able to see how it is inside.

At this moment, I am thinking of putting back the original spark plugs (they were functional when I replaced them) and briefly start the car (if the HV battery has enough juice to turn it over) to see what happens. I am not expecting a miracle at this moment, but this would at least eliminate the spark plug issue.
After that, the coils (especially #2) are my target. I can clear the engine misfire code, swap the coils and see if the misfire code will follow. The issue here is that it may take a few minutes (or more) before the new code is set. It may be too much for the poor engine to run in that condition. I know I made it suffer for the 3-mile journey home that night. I regretted so much later.

So, please let me know what you think.

 

Based on your suggestion, you are suspecting a blown head gasket. That was my initial thought, but I never lost coolant. Maybe the leak was so minimal that I didn't realize the coolant level shifted in the reservoir. Who knows?
I would like to see the inside of the cylinders visually as well. I will try to obtain one of those borescope cameras. I think the ones work with smart phones are very affordable online.

 

Thanks Eddie.
I wasn't aware there are borescope cameras with front and side. All the ones I was checking have front only cameras. Good thing I didn't buy one. I will carry on the spark plug test soon.

 

Hi guys,

An update for those who are following this thread. I was able to fix the car. The culprit was the #2 coil. I carried out the test as I outlined above. I cleared the code; put back the original plugs. But before starting the car, I also swapped #2 and #3 coils because I had a good feeling that this wasn't going to be a sparkplug issue since they came out pretty okay to me. My plan was to run the car till the new code is set and then read the code to see if the misfire would move to cylinder #3. However, I wasn't sure if I could run the engine till I get a new code.
And what I feared happened exactly. Upon staring the car, engine sputtered a bit (this always happens after not running the engine for several weeks. I guess some condensation inside intake) shortly after, it cleared this (took a second or less). Then it started idling okay for maybe 1 or 2 more seconds. And all of a sudden, started knocking like she wanted to part from the chassis. I don't know how I reached the power button to shut it down (I have it on video). I just don't want to think that this engine was running in this condition during the last mile of that journey home that unfortunate night.
I checked with some hope to see if there was any code, but no code was set. While I was driving that night, it took several minutes for the code to be set so there was no way I was going to crank that engine once again. I went with the next most logical thing to me and replaced the #2 coil.
The OEM coil online price was $88 plus shipping. Not bad but I didn't want to wait for a week. Local dealer wanted $130 for one coil. I decided to buy a Duralast from AutoZone for $77. I trust Duralast brand, I used many of their products with success.
So, after the coil replacement, the car started idling nicely. I let it run for the warmup cycle (close to 5 minutes. HV pack was pretty empty).
I did not see any abnormality in the engine bay; did not smell anything funny. I then started her two more times, and she did good each time. I didn't test drive the car since it was partially disassembled and trapped inside my garage. I will test-drive it over the weekend and then will pull the HV modules out to test. During this repair, I realized my busbars were severely corroded (that greenish buildup was almost on every single screw). My HV pack hasn't been doing well lately and I once got the infamous P0A80 code. It didn't come back for a few thousand miles since I cleared it, but I know the pack is deteriorating.
Well, I am very glad this didn't go beyond a simple coil replacement. I didn't have energy to explore everything in there.

Thank you for your comments and support.