Atkinson Blow Back and P0171

I think you mean to say that the intake valve is held open for the early phase of the compression stroke. That lets some of the intake fuel air mixture flow back into the intake manifold. (The sequence is intake, compression, expansion, exhaust.)

Burned exhaust does not travel back into the intake, but there is some blowby exhaust in the crankcase that comes in through the PCV system and, in the 3rd gen, raw exhaust comes in through the EGR system.

I'm wondering how many miles your car/s had when it or they threw the P0171. I've been working part time in a shop specializing in Prius and I don't think I've ever seen that. However, we always clean the MAF sensor as part of the throttle body cleaning we do on all the cars we sell, along with an extensive list of other things we do to them.

 

That is interesting My generation 3 is experiencing this problem now cleaning the MAF Sensor made a huge difference but didn't stop it all It now seems a lot of people are having problems with fuel delivery and fuel pump with the no start and the Gen 3 something I need to take a look at given this car's history. My generation two on the other hand at $300,000 mi I've had it for the last 120 has not had anything cleaned it burns a very little bit of oil for a one NZ and drives and does extremely well The other day when the Gen 3 was acting up I went ahead and cleaned the Gen 2's sensor The Gen 3 sensor I was cleaning was the map sensor which is right next to the throttle body which had oil and liquid in that hole The MAF sensor which is in the air cleaner hose I did unscrew the Philips screws and clean. But it made no difference The map sensor made the most difference in the generation 3 which is having the POAOF 3190 codes.

 

Have you seen infinity's latest design engine that is Atkinson cycle variable everything no crankshaft weights It is very cool but I don't like that Atkinson nonsense at all so I'll probably be skipping right over that infinity technology but it is very cool just watch the program on it the other night

 

Split decision. Jerry's right that the Atkinson effect is from closing the intakes later, beyond the end of the intake stroke and partly into the compression stroke, so that some of the unburned charge goes back out instead of being compressed. That makes the engine's compression ratio smaller than its expansion ratio, which is the Atkinson magic. (Atkinson originally did it, not with valve timing, but with a really weird piston linkage making the intake and compression strokes really shorter than the expansion and exhaust.)


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Jim's right that it's possible for some exhaust to be pushed into the intake. That can't be by "keeping intake valves open for the early phase of the exhaust stroke" because they're already closed, of course, for the compression stroke. What can happen, though, is they open early, in the late stage of the exhaust stroke, before the next intake stroke begins.

That happens when the valve timing adjuster is at the early end of its range, opposite of where the Atkinson magic happens, which is the late end of the adjuster range. So it isn't really an Atkinson effect; it's a different effect the engineers get by going to the other end of the adjustment range. Gen 2's intake valves can open as early as 18° BTDC in the last part of the exhaust stroke. More details are in this post.

 

I believe that's how infinity's new system works well not so new but very similar as this adjustable stroke business or what have you were talking about here drawings look similar

 

I hope you also cleaned the sensing elements that are used to actually measure airflow.
They are fairly fragile, usually I hit them with just the MAF spray.

Deposits on these will insulate them which results in the MAF underreporting airflow. Less measured air = less fuel injected, and the feedback system has to "add more fuel back in" to achieve the target A/F ratio. High positive fuel trims set the P0171 code.

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