Misfire under high load

Hi all!

I hesitate to start a new misfire thread, but I have read through dozens on here and can't find one that quite matches my symptoms.

I have a 2012 Prius v 5. 227,000 miles on the odometer and about 127,000 miles on the engine (which was replaced by the previous owner at 160,000 miles with a used 60,000 mile motor). I've owned it since 180,000 miles on the odometer.

I suddenly started getting a flashing check engine light when above about 80% throttle for over ~10 seconds. Usually when I am merging on to the highway. I can't feel any misfire with "the seat of my pants". I had a code for P0303. Swapped coil packs on cylinders 2 & 3 and reset the code. When it came back, I had P0301 and P0304.

Here's what I've checked so far. I cleaned my EGR circuit when I got the car, and it was fairly clean then. Just cleaned it again to rule it out (it has been 47,000 miles) and it still looked good even before cleaning. I also replaced the spark plugs at 180,000 with OEM plugs. Removed and inspected them all, they are still in good condition and still at 0.040 inch gap. My coolant is still exactly at the full line, hasn't moved even a hair since I changed it when I got the car 2 years ago. This car doesn't consume a drop of oil (still amazing to me, all the cars I've owned before this would use at least a quart between changes). I cleaned the throttle body and MAF, then disconnected the 12v battery for an hour to reset everything. Still getting misfire codes on cylinders 1 and 4.

The coil packs all say Denso on them. I'm a little hesitant to replace them considering the misfire didn't move from 3 to 2 when I moved that coil pack. Seems unlikely to me to have more than one go bad at a time. I'm wondering if it's possible a crank position sensor issue, like the signal quality is low and causing it to think there's a misfire when there really isn't?

Interested to hear anyone's thoughts or suggestions.

Thanks.

 

Good thinking. I took a look at the freeze frame data when the code set.
SHRTFT1(%) 2.3
LONGFT1(%) 7.8

 

Update: shortly after posting, I did replace the coil packs with brand new OEM. It made no difference in my symptoms, still getting misfire codes on 1 and 4 under high loads. No change until today.

Now I'm getting heavy, noticeable misfires at idle and low throttle. When acceleration normally, or driving at speed it runs smoothly. And I still get a flashing check engine light under full throttle. Now getting P0300, 1,2,3,4.

I removed my fuel injectors and cleaned them, blew some carb cleaner through them, and re-installed. No change. Not sure what to do next.

 

Yes I did. Wasn’t too bad but I cleaned the intake, the cooler, and the egr pipe first. Since I’m misfiring at idle, EGR should be closed, yes?

I just tried running it with the MAF unplugged, no change.

 

Update: this issue is solved! Ever since I removed, cleaned and re-installed the fuel injectors, my original issue of flashing check engine light while accelerating to highway speed has gone away. I've put around 500 miles on the car since doing that and clearing the codes and I have had no codes re-appear, no flashing check engine light.

That said, I do have this new issue where at idle or very light throttle, the car feels like it's misfiring. It is also making the classic prius engine rattling sound. No codes though! I unplugged the spark plug coils one at a time to confirm that the issue was not tied to any 1 cylinder. I threw in the towel on being able to diagnose this myself and took it to the Toyota dealer. They diagnosed the issue as a failed transmission input damper. After watching some YouTube videos on it, their diagnosis makes sense to me (and would explain why there's no codes). They quoted $4,200 to make the repair (LOL), so I will be starting a new thread to share my experience on DIY repair.

 

I don't think that's the issue in my case, I flushed my coolant around 50,000 miles ago and have added 0 since, it is still exactly at the full line. While trying to diagnose the misfire, I took it out on the highway to get nice and hot, then pulled the spark plugs and borescoped the cylinders to look for coolant dripping in. I have a side view borescope and was able to get a nice clear picture of the headgasket all the way around the cylinder head, no evidence of coolant leaking.

I'm attributing the failure to high mileage, and driving with my highway misfire for a few months while I was troubleshooting it (admittedly longer than I should have let it go for).