My 2005 Gen 2 Prius has developed an strange intermittent issue over the past month (reproduced only once so far). While driving under load (especially climbing long grades), the engine suddenly misfires badly for a few seconds. It then either continues running "normally" with very low power or triggers P0A0F, forcing me to coast and power cycle the car. First occurrence: ~1 month ago on an interstate onramp; had to coast off with P0A0F. Unfortunately I just had to reset it on the side of the road to make it home and didn't think to screenshot the codes or save the freezeframe data. Second: Today, after ~1000 miles of normal driving since the first. Engine returned to running normally after ~5 seconds, and I was able to make it home, albeit on noticeably reduced power. Techstream scan today shows: P0171 (System Too Lean Bank 1) P0442 P0446 Live data at idle @~155F (heater on to force engine run)and partial throttle ~1600rpm shows: B1S1 STFT ≈ -21%, LTFT +44.5%. The lean code combined with the evap codes makes me think perhaps a cracked evap line and faulty valve? As I've only had it happen twice within the past month/1k miles, I find it difficult to believe a leaking gas cap would be the source of that issue. Not sure what to make of the fuel trims either in this case, but fuel economy is noticeably down over the past 1k miles since the issue first happened. Any ideas on where I should start looking? I'll clean the MAF tomorrow as a sanity check, but it seems very odd that it'd be intermittent like this.
I'd be wondering about the fuel pump capacity or fuel filter. Seems like fuel delivery isn't keeping up under sustained high demand.
Yep; over 20 years of pumping fuel into it, there's probably a bunch of crud that's made it into the fuel tank - clogging the filter sock too. You can verify by placing a fuel pressure gauge on the fuel rail. The EVAP system has NOTHING to do with this issue. You can run any car without a fuel cap; but you'll get a bunch or EVAP error codes. The engine isn't going to stall-out or die on you. You will fail a CARB state emissions test with those active codes.
On a normal car that wouldn't be so terrible, just pull it out and clean it. On this car though, is there any kind of fix other than replacing the whole tank? I mean, I suppose one could blow out the fuel line by unhooking it at the tank, and if there was some blockage there it could be cleared. But I agree the problem is more likely in the tank, so that wouldn't help at all. There are products which claim to be fuel tank cleaners, like this one (no personal experience with it) Star Tron Fuel Tank Cleaner - Concentrated Gas/Diesel Formula – Star brite Distributing, LLC I expect the most likely outcome is that it would finish off the fuel filter, once and for all.
