P0303 P0101 P0171 P219A | Severe misfiring at low RPM

Today out of nowhere our Prius started misfiring, at low RPM. I noticed a shaking when depressing or releasing the pedal (where the rpm is low for a moment) but not at higher rpm. The check engine light started flashing.

Unforunately I didn't have the ODB tool in the car so I went to the nearest auto parts store to have them read the codes: P0303 (Cylinder 3 Misfire Detected), P0171 (System Too Lean), P0101 (Mass or Volume Air Flow A Circuit Range / Performance).

The P0101 I found interesting; so I thought maybe there was something wrong with the mass air flow sensor (or its circuitry), causing the other two troubles. So I tried unplugging the MAF, but that did not improve anything at all (and triggered P0102 P0113), which rules out the MAF (at least the unit itself).

Went all the way back home with this; there I checked the codes with my tool (Hyper Tough ODBII code reader); found another code P219A (non-standard code meaning "Bank 1 Air/Fuel Ratio Imbalance"). Well the only way that could happen is if one or more of the fuel injectors is injecting a different amount of fuel than the others! So that tracks it down to an issue with the fuel injectors... So I thought maybe it's a bad fuel injector? But then how could that have caused P0101...

Pulling the plug on injector 3 caused constant misfiring at idle, identical to what was experienced before. So this suggests it's because of the injector not injecting fuel. But with it plugged in, it only misfired sometimes... the symptom at idle is kinda intermittent; sometimes it idles ok, sometimes it misfires lightly/sporadically, sometimes it just goes CLUNK CLUNK CLUNK CLUNK CLUNK (like when injector was unplugged)...

To test whether it's a bad fuel injector, I swapped injector #2 and #3. If the injector was bad, I should get P0302.

Cleared codes and did a few miles of test driving, some floored, some at low acceleration. (btw maintenance mode is fun lol; no acceleration delay due to traction control; also vtec thing (?) roars louder without the air box (i just put back the part with the MAF)). The behavior was reliably reproduced like so: With light acceleration, where on the "Hybrid System Indicator" the meter is just past the middle line (where the engine kicks in), the engine constantly misfires, shaking violently. But with medium or light acceleration (havent tested medium very much though) the engine seems to run fine. When stomping on the pedal (0-100%), engine misfires for a moment as rpm rises through the low end, but roars fine through medium to full load and acceleration seems fine.
And unlike the idle, this behavior seems to be consistent.

Checked new active codes once I got back: nothing but P0303, three instances of it. So it couldn't be the fuel injector.

So at this point I'm not sure what to do next. I've been thinking it might be an electrical fault, related to injector 3 and the MAF circuit, but idk. I recorded a lot of rough video I could sort/edit to show if you want.

 

I had forgotten; I was also thinking of a failing ignition coil. I believe they can randomly start failing like this, but I didn't see how it would cause a P0101. Although now I realize that it could have possibly caused P219A because the fuel is unburnt?

I unplugged ignition coil #3, and behavior was very similar. However I did notice a slight difference in sound when plugging and unplugging it. But symptoms were identical; even sounds fine at higher RPM, but power is noticeably less. I think I might've noticed such reduction in power when we returned home, but not during the previous test run... not sure.

Tomorrow I'll disassemble the windshield wiper stuff as necessary to take out the ignition coils, and swap #3 with some other cylinder. If the misfires are detected from that cylinder after that, then that must be it.

 

So I swapped ignition coils #3 and #4. I also checked their spark plugs before that; #3 was wet with gasoline and a little darker than the others, but otherwise looked fine and had the same gap as #4. Cleared codes and did 5 miles of test driving; btw so the check engine light always flashes under high load, when engine doesn't sound too bad; but does not flash at low rpm when it's clunking. Shaking happens very close to the middle line on the Hybrid System Indicator; medium to high load does make it go away.

Checked codes... I'm not sure how to differentiate pending codes from active codes on this particular OBD tool, but I think it's the P0303 again. There is no P0304, but there is a P0300, P0301 and P0353, which I believe are pending codes from previous/momentary incidents.

So it's not the ignition coil. I wonder if this might be a "fouled plug". I'll try swapping plugs next.

 

232k

Coolant is slightly above full, exactly where it has always been for over a year now since I refilled it after working on EGR cooler.

No other symptoms of a blown head gasket.

 

Swapped plugs #2 and #3. I didn't get the MIL to turn on but found a couple of P0302's pending.

Fouled plug??

 

I changed the spark plug with the best one of the original plugs that were changed somewhere around 150k. They looked better than the second set of plugs; Autolite Iridium which were changed out at 227k. The current plugs are OEM Denso SC20HR11 again, with only 5k miles on them so far.


left one is plug I took out, right one is old plug.

Engine runs fine now.

Also this is probably unrelated but I noticed something odd about these plugs; the little iridium tip seems to be missing on all of them.

Here's a better look at them; the original OEM plug on the right with ~150k miles still has its tiny cylindrical tip, while this "OEM" plug on the left that only has 5k miles on it, seems to be missing that and only has its large conical section.


Here's an image from August 9 when I put these plugs in:


As you can see, a lot of the tip seems to have eroded, and it's only been through 5k miles!
So here's the thing. The Denso SC20HR11 on Amazon was about $14 each. But on eBay, you can buy a pack of four plugs for about that price. Which is what we did. And the plugs looked perfectly OEM, in the red Toyota/Lexus OEM boxes. Could it be possible that these plugs are counterfeit or defective units or something? Besides the odd loss of electrode tip, they seemed perfectly legitimate.

The other plugs (#2 and #4 so I assume #1) have the same electrode and are working fine so this is probably unrelated to fouling plugs... not sure if I should worry about it.


BTW the images on priuschat are reduced in resolution so here are the originals if you want to see better https://photos.app.goo.gl/Sixwn4jrAvXpN4hs8

 

Last sunday PG&E shut down our power right when I was on the toilet
Then since next day our cable service has been down as well!

So on Sunday after the power went out I set up the Prius to use as alternative power and something strange happened...
When it started up it puffed out a lot of like smoke/steam... I believe it has worn valve stem seals and it is known to burn oil sometimes after a lot of engine braking and/or at cold starts... but this did not smell like burning oil; it smelled strange, and bad... kinda like some kind of burning plastic... not sure how to describe. But it irritated my respiratory system for the rest of the night and made me feel bad
After first start it gradually went away...
Next couple days I also observed some smoke/steam after the first or second start up after getting home. And as usual it did not last long. However it seemed to continue blowing out a little steam from the tail pipe, held my hand in front of it and it condensated, evaporated later, so seems like water... Also didn't smell so bad at this point like it did at first... but yeah that is strange... never experienced steam and that strange smell before... and well so far coolant level is not noticeably different but I will keep checking it.

Oh well only four minutes left on this library computer, then library closes a few minutes later and then back to home with no telecommunications

Edit: nvm power and cable was back when we got home

 

Coolant level appears to have reduced At cold it was slightly above full, but now it was just at full.

I put the car in maintenance mode to let it idle and monitored the tail pipe output. At first there was the familiar burning oil smell for a moment. Then there remained a very faint amount of steam coming out, hard to see but condensation noticeable on hand. But while idling it gradually blew more and more steam... at some point there was a change in engine noise and a significant increase in steam... then it gradually reduced but remained blowing a noticeable amount of steam. All of which has that strange burning plastic smell. I think it smells like burning PVC (ever tried to fuse electrical tape with a soldering iron?) but I'm not sure. Certainly not like coolant or oil, but I guess the antifreeze is reacted somehow in the combustion chamber.

https://photos.app.goo.gl/4bLye9xZesBshJeFA

Oh also I did also try a compression test. I didn't have access to the internet to find how to do it properly (turns out you need the special ODB tool which I didn't have either) so I did it by starting the system and depressing the accelerator; it would crank for a few seconds until it throws an error; then I'd have to restart the system to crank it again. Annoyingly it took three or four times to reach the maximum value for each cylinder (gauge rose so slowly... I think maybe because of the long hose.). From what I saw it looked like compression in all cylinders are fine (~140 psi). but I'm not entirely confident I reached the maximum value for each cylinder.

 

So about the spark plugs. So we got counterfeit plugs, and now the gap appears to be too large, which combined with the carbon soot is I think why the plug fouled (maybe a genuine plug with proper gap would have continued working and cleaned itself). The question is what caused the soot... maybe a splash of oil got on it somehow from leaky valve stems (all spark plugs have oil on threads and have for a long time). But also what caused those other codes, P0171 and P0101. I only got those codes after the issue spawned; on the test drives after clearing those, I only got misfire codes. So it seems the P0171 and P0101 is related to something that happened that fouled the plug. And now that the head gasket appears to be blown too, maybe that was the moment that it actually blew? I don't see how it could have caused those codes though...

So I think I will find a set of real iridium spark plugs and replace all of them. I still have the wiper stuff out for that, and also I hope to replace the cracked windshield soon, if I can find a used one cheap. Also should clean the EGR circuit again as I could here pinging with the wiper stuff out. And now looks like there may be an engine rebuild in order as well, before the wipers get put back in.