Sharing common Prius trick

What is that? Or is it a case of “if you have to ask”?

 

i've never heard of this trick before. can you explain how it works, and what mpg's would she have gotten if she drove right off?

 

Closed loop.
The oxygen sensor is warmed up, and the ECU uses its input for adjusting the fuel fix. Open loop, it uses preprogrammed fuel maps, which generally run rich to avoid NOx production.

A Scangauge or like can tell you if the car is in closed loop or not. I remember it coming on very quick in the HHR, less than a minute. The old Civic VX had an oxygen sensor that was heated to speed up its operation; maybe the tech is now standard.

 

I was hoping for a refresher here, but the naming pattern is not the same:
The Five Stages of Prius Hybrid Operation | PriusChat

 

In the formal world of printed words there are people called editors. A PriusChat wiki editor would, among other things, direct contributing authors to prepare lists of tips and tricks, specific to each model. First level is "what to do". Second level, clicked within, would be "why it works".

Many (or most or all) of these tips are spread across PriusChat landscape. Posted over years and decades and commented upon in their local threads. And there they remain.

I can imagine only one way to 'make money' off this activity. I shall call it The Prius Book. Led by PriusChat overlords and expanded by participants here. Many of whom I could name

There could also be intro chapters on Prius history through time, Descriptions of each model with production runs etc. It is possible that Toyota would throw some money at the project. I know some publishing-house agents and maybe others here do as well.

 

Lamda mode... a term from the land of satire.

 

does it help with emissions?

 

Emissions, efficiency, and performance.
You want the fuel-air mixture in the engine to be stoichiometric; the ratio of fuel to oxygen to be at the point that both are completely burned. Too little(lean), the engine can't make its max power, and NOx out the tail pipe goes up. Too much(rich), and it wastes fuel while increase HC emissions. The oxygen sensor does as its name suggests. If it detects oxygen in the exhaust, the ECU increases the amount of fuel in the mix until no more oxygen is detected.

 

Can you explain this further? What setting and how can you tell if it's open or closed loop?

 

Among the regular parameters that can be reported is a fuel system loop one. It will display OPEN LP or CLSD LP depending on which the car is operating in.
» User Manuals

In my cars the switch from open to closed on start up was quick enough that I would miss it while doing other things. IIRC, I had the display on to figure out when the HHR went into DFCO. It would go to open when the car cut fuel to the engine during coasting.

 

Any engine damage not letting it warm up?

 

No. The car just burns a little more fuel during the short time it is in open loop on start up. From the OP, it seems that extra fuel is more if you drive off with the car in open loop vs letting it idle until it reaches closed loop. Depending on the ambient temps and driver's start up habits, you may not have to actually wait for that to happen.

 

Has Toyota fixed this in newer generations?

 

I don't think I'll change my driving habits; just start it up, get going, driving extra gentle the first block or two.

One thing we do, is virtually without fail, year 'round, before a cold-start: plug in the block heater for a couple of hours.

 

Odd that I should read this so long after it was first published. In another car the manufacturer heated the O2 sensor (thus a specific fault code if the heating element wasn't doing it's job) and used (via the ECU) the air flow meter and the O2 sensor results to adjust the a/f mixture to achieve the most effective burn.

So never had to idle, I just climb in, start the engine, buckle my seat belt, and back out and drive the first mile at around 25 MPH which is the limit. In my hybrids since '12 I'd do the same and always achieved average MPG especially considering the proportion of my trips that are 4 miles and then stop and shop before returning home after a few stops. I live in a moderate climate that varies from 5 to 105F but is seldom in those extremes and the car is always parked in a not heated garage but never as cold as the outside temperatures.

If the a/f mix is optimized frequently, why (after the first mile/minute) would the warm up have any effect on a modern car?

This is description probably 20 years old.

" The O2 sensors do just that, sense the amount of O2 in the exhaust gas relative to the amount of O2 in ambient air. Perfect combustion of a perfect mixture of air and fuel (around 14.7/1 air/fuel ratio) leaves behind only CO2 and water as products of combustion. All the oxygen gets consumed in the combustion and combines with all the carbons and hydrogens. If there is not enough fuel (lean mixture), then all the fuel gets burned leaving some oxygen left over. Conversely, if there is too much fuel (rich mixture), then all the oxygen gets burned leaving behind extra hydrocarbons (fuel). Now an oxygen sensor outputs a voltage between 0 and about 1 V depending on the difference between the amount of oxygen in the exhaust and the amount of oxygen in normal air. If there is a lot of oxygen in the exhaust (lean mixture condition), the sensor outputs close to 0 volts. Conversely, if there is no oxygen in the mixture (rich condition), then the output is close to 1 V. These O2 sensor voltages are read by the computer. This is the feedback loop that tells the computer how the engine is performing with regard to air/fuel mixture. It's impossible for the computer to hold the exact perfect air/fuel mixture constantly, so the way mixture control is designed is for the computer to continually adjust the mixture from very slightly rich to very slightly lean and back again using feedback from the pre-cat O2 sensors. This means that the pre-cat O2 sensor signal will oscillate back and forth from high to low to high to low voltage as the computer adjusts the mixture. In a normal running engine at idle the signal goes from low to high voltage and vice versa about every 1 second, with a transit time from low to high (or vice versa) being about 200-300 milliseconds. This transit time is important because as an O2 sensor ages, the transit time gets longer, and eventually it can get too long such that the computer will call it a malfunction and signal a check engine light and fault code for a slow responding O2 sensor. O2 sensors need to respond to mixture changes quickly so that the computer can keep up with the proper mixture adjustments.

So the bottom line is that the pre-cat O2 sensors should oscillate between about 0.2 to 0.8 volts regularly (about every 1 second at idle) in a healthy engine.

The post-cat O2 sensors are identical to the pre-cat O2 sensors (same voltage outputs). They are there only to monitor the performance of the catalytic converters. So, as discussed, the pre-cat sensor signals are oscillating between 0.2-0.8 volts. Once the exhaust gasses pass through the catalytic converter, most (all, in theory) excess fuel (hydrocarbons) will be combusted thus reducing hydrocarbon emissions. The cat uses oxygen in the exhaust to combust the fuel. So what you end up with in the exhaust after passing through the cat is a gas mixture that is reduced in hydrocarbons and reduced in oxygen relative to the mixture entering the cat. The post-cat exhaust gas mixture should be CONSTANTLY low in oxygen if the cat is doing its job of burning excess fuel. Therefore, the post-cat O2 sensor signal should be a constant lower voltage reading (not oscillating). So, if the post-cat O2 sensor is seen to oscillate just like the pre-cat O2 sensor, that means that the post-cat sensor is seeing the same gas mixture as the pre-cat sensor meaning that the catalytic converter isn't doing its job of burning excess fuel. The computer monitors the post-cat sensor and compares it to the pre-cat sensor. If the signals are similar, it assumes the cat is bad."

What evidence is there that a recent US Prius or any other Toyota with functioning and yearly tested emissions controls in place operates any differently?

 

There is nothing to fix. What the nice description above left out was that the oxygen sensor has to be hot to work. A basic diagnostic is to hook it up to a multimeter, and then hit it with a blow torch. Until it hits operating temperature (over 600F), in sends no signal to the ECU. A heated sensor like the 1980's Civic VX had will speed up the warm up, but it isn't instant

No O2 sensor signal, and the ECU defaults to fuel trim maps in memory that state how much fuel to use based on air temperature and the load on the engine. These preset fuel maps tend to be on the rich side. They might be more rich when the engine is under load vs. idling, which is why Bob is reporting better fuel economy with waiting a minute.

If you turn the engine on first thing upon sitting in the car, it could switch from open to closed loop by the time you buckle the seat belt.

 

Bob's advice is terrible. Again. He's identified a 'flaw' that does not exist. Again.

It might have a positive impact if it were a conventional drive train with a brand new battery, but that's not even mentioned. This so called "secret" is telling people to try to waste time and gas for no benefit.

Every modern car has a similar calibration cycle, and the settings are stored when the car is turned off. When the 12V battery is disconnected the car has to repeat the calibration. It does not need to calibrate every time you start the car.

 

I was beginning to think I had misinterpreted his intent.

I once registered 66 MPG on a trip.
It was 2.3 miles to the grocery store.
Partly down hill.