I do mostly stop and go driving in my truck and my driving style is as follows: I use heavy throttle application and shift very short, such that I rarely go much above 2000 -2200rpm but pretty much floor it whenever accelerating. As soon as the truck starts to make some power I upshift to keep it between 1500-2000 where its a complete dog. The logic is that I can reduce pumping losses by keeping the throttle body open, reduce frictional losses and wear in the rotating assembly, but still accelerate slowly and drive conservatively despite keeping the petal to the metal. I get about 17-18mpg with 30" m/t tires in my 4x4 ex-cab truck. Engine has about 240k burns a quart every 3k miles so compression is fairly good I think. I also have a pretty new upstream O2 sensor, valves adjusted, new timing chain, 40k on new head.

I do feel like I should be getting better mileage. I'm beginning to wonder if the computer adjusts the mixture based on the TPS, such that it runs richer or even enters open loop at higher throttle positions for maximum power even at lower rpm, negating any benefit of this driving style. If not, what is the purpose of the TPS anyway? Is it only for cold-starts when the O2 sensor is cold and the engine is in open loop?

 

So you floor it all the time and think you should be getting better mileage?

 

One of the books does mention it exits closed loop when cold, and when receiving a more than 3/4 throttle signal.

18 isn't horrible.

 

s That's exactly the information I'm looking for, thank you!

 

"Power enrichment"

 

A big use of fuel on automotive engines is a thing called tip-in. It's the same thing a accelerator pump on a carburetor does. When the throttle opens quickly it dumps extra fuel. You want to accelerate slowly. High rpm does not use more fuel than lugging the engine at low rpm. It's the opposite. The throttle being open more = more fuel is injected to maintain the correct fuel mixture.

 

I get 20mpg on 33s not driving like an ape. Not sure why you think flooring it is the right idea...

 

To give the engine more air. The intake valves are open longer at low rpm, and unless air pressure completely equalizes in the intake, more air can be ingested per stroke. This creates higher peak combustion pressure which is directly related to work efficiency. Additionally, there are less frictional losses in the rotating assembly, the transmission with power-sucking GL-4 oil, water pump, fan...we're only talking about 35 or 40HP output at those engine speeds. Even a measly 1HP (746W) of losses would be nearly 0.6MPG or 3%.

Of course the computer would need to run lean. Instead, it sounds like it richens the mixture at high throttle settings to produce absolute maximum power...I mean who wouldn't, in a 100HP truck?

 

You're ignoring the added influx of fuel that goes along with it. Flooring it then short shifting before you even get any power is such an inefficient way to run an engine. 18mpg is average at best for these trucks.

 

I love this. I’ve been chasing the best mpg for about a couple years now. My truck has been in the family since new so I’m real confident it is an optimal running 22re. When I received it in my possession it was in need a tune up, a bad oxygen sensor. On the trip from Florida to Texas after being shipped from Puerto Rico I averaged 18mpg with 28” tires, 4.10’s and the less than optimal state of tune. After getting it to Texas, I immediately did a full tune up.
cap, rotor, wires, filters, spark plugs, fuel filter, tps, efi temp sensor, oxygen sensor. It ran better but still only got 18mpg. I noticed the alternator was making noise, replaced that. It felt like it had better throttle response but not much change in mpg. Some time later it developed a rough idle, intermittent no start. After lots of parts throwing at it(I’m a Lexus/Toyota parts guy) it turned out it was a bad ecu. Before that I had replaced the fuel pressure regulator, the fuel pump, air flow meter, egr valve, modulator, and cold start injector time switch. I also replaced the cat. I also added 31’s with 4.56 gears. While my speedo was a little off I still calculated the mpg correctly with a gps. I also added a turbo 180 degree thermostat and advanced the timing to 8 degrees. Pulls very good off idle. With this setup it averaged 19 mpg. My original ac compressor was acting up so replaced it and all the idle pullies. I went to 32” tires for the lift and to also correct my speedo. It is dead on now. My mpg dropped to 18mpg. I then did the best mod of all. Honestly I should have done this from the jump. I removed the Lund visor my father put on it way back in 1993. My mpg jumped to 21 mpg. I even got 23 on one stretch of just highway hypermiling. I plan on backin off the timing a bit so I can run at least mid grade. I have a 4000 mile round trip trek from Houston to Boston and back planned for the summer and every little bit helps save. I will be carrying two motorcycles so I hope I can average at least 19 on mid grade.

 

Oh and I accelerate slowly and smoothly, shift around 2600 rpm, no wide open throttle lugging like the op mentioned. Max cruising speed on the highway 70mph. She will top out at 87 mph on level road.

 

I propose you try shifting between 3200 and 2800, since 2600 is just a little below (2800) when the torque curve of a 22r(re) starts to ramp up. This should get you a little closer to the 26mpg spec.

..
There are quite a few things you can do to improve your MPG. Let's start with aerodynamic drag cause over 20mph it's a big big factor (if you want to test this it's really easy to see on a bicycle, try pedaling an upright cycle versus a low slung recumbent cycle).. Running with the tail open is a bad thing, that pocket of air we who rode in truck beds remember gives you a more tear drop shape vs the laminar flow you get wth the gaye down. The higher your lift the more drag, this has to do with you spilting the air in two parts, think about a low slung F1 car versus a square brick (Toyotas are bricks, and I'm OK with that) , when you force air up its only resistance is the air above it but when you try to force air down its pressing against the planet and all the air on the other side of the planet so you're compressing all that air downwards ..

Now let's talk F=m²a. The faster you want to accelerate the more force (read: Horsepower, HP is something like 33k ftlb/min if I recall correctly) is required. So person A who accelerates to 35 mph in 30s uses much more energy that person B who accelerates to 35 mph in 45 seconds.

..

Pumping loss due to the throttle plate restriction due to its angle is pretty negligible at the volume we're using on the street.

..
The Vs and VTA(maybe this is THA, shrug its late) signals are important. Vs is measured by the VAFM and it is essentially engine load. VTA is your throttle position, this signals the ECU "I want to accelerate at such rate". So if you have a high Vs (load) and a high request for acceleration (TPS angle.. There let's use that one.) You're telling the ECU " We have a high load, deliver more fuel." And "I want to go faster, deliver more fuel!" These combine I to "Hey ECU dump as much fuel as I can burn please."

..
Bang for your buck? Service and repack your wheel bearings. A little bit of fresh grease and a proper preload, might net you a few more mph of coasting down hills (read: less drag)..

 

Pumping losses aren't really negligible. For a 2.4 liter engine running at 2500 rpm at 10" of vacuum, the pumping losses are about 2.6 horsepower. That's about the same as 2 or 3 air conditioner compressors all running at once.

As I recall, a 1st or 2nd gen 4runner takes about 20 horsepower to move it at 60 mph. You can measure that yourself doing coast down tests. So, if you get 20 mpg at that speed, the pumping losses are worth about 2.5 mpg.

Modern engines are increasingly using sophisticated valve control to reduce the effect of pumping losses. When you're after every last mpg, everything matters.

 

[QUOTE=mostmatt;52436876 Additionally, there are less frictional losses in the rotating assembly, the transmission with power-sucking GL-4 oil, water pump, fan.[/QUOTE]

Use an electric fan, not much you can do about the water pump.

Power sucking GL-4 oil?????? What does the gear oil service specification have to do with this "power sucking"?

So you're getting about 18mpg city driving, stopping and starting (and idling) with an engine that has 240000miles and burns a quart of oil every 3000? That's not too bad. What's it get on a highway trip?

 

Good to know that there's some potential there..

Though it sounds like fuel map changes would be required to achieve any gains. Makes sense that engines have gone to electronic throttle bodies. I would guess modern vehicles use much more aggressive throttle position and control power output with mixture, timing, etc, at least under low-load conditions.

 

Around 17 usually but that's going 80+. Though I've gotten as low as 9-10 pulling a tacoma excab 4x4 1500 miles from CA to CO over the mountains...not recommended lol

 

Yeah it's an old 8bit MCU at its heart which means it's pretty limited by today's standards and that is before we even start talking about the cost of eeprom/storage in the 80's(!!)

What I said was along the lines of "The throttle plates attribution to the pumping loss" was negligible. (yes I'll dig into that math more when I get some free time) But a wide open throttle also effects the "tuned length" (as designed by old grey beards) of the plenum, as well as the aforementioned "power enrichment" from the tps signal which adds in with the high engine load from shifting early.

..
Shrug like I said 18's not horrible, it's loads better than the 16 mine gets on our country backroads with a 65mph limit. But well I do like the accelerator pedal and +10 psi of boost.

 

I you had one of these http://mpguino.wiseman.ee/eng (instantaneous MPG, along with more other numbers than you could possibly digest) you'd never drive like mostmatt claims. At all points in driving, you'll get the maximum MPG with the lightest foot possible. "Pumping losses" or not.