Active MPG counter and ECO gauge don't add up?

All the gauge angst aside, you're saying it seems like a drop-off in your fuel economy lately? On ours (much less miles on the odo fwiw) it seems like this spring the mpg hasn't picked up much, so I'm thinking what could be the cause.

Reading up on likely suspects, so far I've checked the two O2 sensors The repair manual specs a range for the Ohms, measured at their connectors. I've checked that and they were both within spec. You can access those by removing the engine underpanel (for the upstream sensor) and the (metal) heatshield style panel directly aft (for the the downstream sensor). I'll attach a repair manual excerpt for that.

Also read another suspect is fuel injectors, starting to get clogging. I haven't tried yet, but purchased a bottle of fuel system cleaner, the kind you shoot a little in when tanking up. I'll give that a try and see how it goes. The stuff I got was Canadian Tire's Motomaster Formula 1 Extra-Strength Fuel Injector Cleaner (bit of a mouthful ). It's indicated to have PEA (polyetheramine) which is often mentioned as an effective cleaner. In the States Chevron's Techron Fuel System Cleaner is a good candidate.

Air filter is traditionally mentioned, but with fuel injected engines, computer controlled, unless the air filter is really filthy, it's not likely to be impacting mpg.

Have the spark plugs been changed? I would think so, by this mileage.

Maybe brakes are dragging, for one reason or another. Immediately after a good drive, go 'round and feel all four wheels, see if any are unusually hot.

Also look into:

Intake Manifold cleaning
EGR System cleaning
Oil Catch Can install

There's threads on these here, and @NutzAboutBolts has some excellent videos.

 

Your tire psi should be 32psi, 46 and 44 psi is just over kill and will cause your tires to bald on the inside more than the outside. Also, having a higher psi doesn’t help with your fuel economy, having the proper psi should be the ideal for your tire life and handling.

 

The Toyota spec is 35/33 (front/rear). Personally I'd do maybe 36 all around, just to keep it simple.

 

You can check your tire max psi. I think mine was 40 or 44 psi or so, but I’ll have to check.

It should be 32 psi when the car is cold or early in the morning. When you drive and it heats up, it’ll increase the psi. You can have the front to 35 psi and rear 33 since the front is heavier than the rear due to the engine. I usually set mine between 32-35.

 

One of my Prius sets says 44, the other set says 50. The seasonal set currently on my other car says 51.

Some tires list 40 max while setting the beads, but that is different than road operation.

Some of my tire labels have indicated that the full tire load rating applies only at that max sidewall pressure. Lower pressures require reduced loads. Other labels have been more vague. When renting cars in Europe, we have noted several car pressure labels calling for higher inflation pressures when the car is fully loaded. But such multiple-choice pressure labels appear too complex for the American market.

Hogwash. The door frame label says 35/33, on Prii with 15" wheels. Take that as cold morning minimum. There are no 32s in there. The 17" wheel versions do have lower recommended pressures.

Plenty of us hypermilers challenge all of that. Even both my independent car shops dispute your later sentence here. My shop for the other car (not the Prius) defaults to 38 psi as a reasonable compromise between mpg and comfort, unless the customer asks for something else.

As for examples of tires going bald in the middle from inflation higher than the door label but not exceeding the sidewall max label, I want to see examples of it on modern steel belted radial tires on passenger cars. (Old fashioned bias ply tires, and trucks, specifically excluded.)

Tire inflation is a compromise between multiple conflicting goals. Many of us believe that the manufacturer recommendations overweight ride comfort, and underweight tire life and mpg. Thus, 'best' pressure becomes a matter of customer preference, varying from driver to driver.

Back in the late 20th Century, those labels also underweighted safety, as illustrated both in the deadly Firestone Tire / Ford Explorer rollover fiasco, and in my own household's problems with hydroplaning in our local rains in our Honda and Acura.

 

Because you're a superstitious pigeon. It's okay, we all are.

What I mean: You have very shaky evidence that the car is "suddenly" getting lower fuel economy aside from what you've noticed on an inaccurate factory fuel economy meter. This has happened over the course of a very short 220 miles--barely half a tank--which is not nearly far enough to get an accurate resolution on fuel economy. You haven't controlled any of the innumerable variables that can affect economy--changes in temperature, wind, and weather; changes in traffic and traffic patterns; changes in your routes and driving; changes in the number of stops and accelerations; changes in distance and number of cold starts vs. warm starts. Until you can control for all or most of those variables, it's very premature to blame tire pressure for a problem with fuel economy.

My advice is to leave the tires at the sidewall maximum (44psi for 195/65-R15 tires) (this is the max. cold pressure rating--you can safely run tires at that pressure despite the pressure increase as they warm) (and no, they won't wear faster on the inside or center or whatever else anyone says--I've run my tires at 44psi the entire life of the car, and my previous car as well). Get through a few tanks, and keep meticulous records of distance driven on a tank and fuel pumped. Then, you can look at trends and start to make changes and see what effect they have, or better yet do some coastdown testing and actually measure rolling resistance and aerodynamic drag. Changing the tire pressure and then being concerned with lower fuel economy the next day reeks of confirmation bias and prematurely assigns causality where there may be none simply because you don't have enough information and are making an assumption. Don't be a superstitious pigeon.

 

Apart from the jarring ride, I've started speculating that higher pressures are harder on wheel bearings and various suspension components. There must be some effect: when the tires are at higher pressures they're less able to absorb shocks, increasingly pass them along to the next component. Obviously everything's a trade-off, but I like to stay close to spec air pressure, just a pound or three over.

 

your info is misleading to say the least. modern radial tires don't wear more in the middle with slightly higher PSI. also, the total wear is lower at higher PSI. google for that, it's fairly common knowledge. tires also handle better with higher PSI. the reason low PSI is officially recommended has to do how tire engineers calculate tire loading (some of that is government regulations) and ride comfort is better at low PSI.

 

Unless the ASE has changed in the last 10 years since I’ve took it, then this info isn’t misleading. That’s what they’ve taught us in school and through the ASE testing, I’m just reiterating what I’ve known and seen. So if there’s informations that has been changed, then I haven’t read it or known of it.