keep the engine rpm's between 2100 and 2300 rpm and you will have better mileage. you can't feather foot a 4.0 and get decent gas mileage with a stock cam. use a "moderate" foot.

 

I get 12 on a good day. I gave up on my fight with good mileage. I drive like a grandpa usually, but sometimes I romp on it. Its fun to spin the tires on wet pavement after school and show up my friend with his dad's v8 dakota. The D35 posi is better than the open diff in that pickup.

 

I'm not having this issue, but there is something you have to consider, I think.

When you press down on the gas pedal more, you send more gas into the engine, right? This means more pressure, and so more "spray" to the gas going into the cylinder... which would mean better atomization of the gas. The more diffuse the gas spray, the more than burns, which means better gas mileage, right? That's why people always get higher mileage on the parkway than driving the backstreets; the gas pressure is higher, atomizing the gas more and allowing for better mileage.

So in short, pressing harder makes the gas atomize better, thus better mileage. At least that's my take on it.

 

Your roof rack and rooftop spare tire are really hurting you.

 

Those heavy steel wheels aren't helping either.

 

It's computer controlled. Don't work that way.

 

Been reading and experimenting with gas mileage.

When accelerating, PCM goes into open loop therefore sending more gas in so yes, longer accelerations are not necessary better.

I also found that keeping it in the 2300 range I get best gas mileage no matter what speed. I try to shift at 2000 and it gets there very quickly.

I put in a 6 speed from a wrangler and my mileage went up to 19mpg from about 15. it has a little higher revving 6th gear then the factory overdrive.
I shift more often but it seems like their is always a perfect gear for the speed. oh yeah, I also stroked the 4.0 to 4.7 so more power and more MPG.
(happy dance here)
Other mods: high flow Amsoil cone air filter.
Borla headers with high flow muffler.
Going to put a high flow cat real soon.
my goal is to hit 20mpg. im almost there.
(sorry, I may be bragging here)

 

At Wide Open Throttle it goes into open loop, not just accelerating. If that were the case fuel injection would be all for naught.

 

While I don't doubt what you're doing, everybody else reading this needs to consider that your Jeep is NOT stock, and your numbers have been arrived at with your modifications. So far we have a 6.5" lift, unknown tire size, unknown gears, and a 4.7L stroker. lol

I spent a tank driving around town in 3rd at like 1900 RPM instead of going to 4th once I hit 60 KM/H. Did not observe any difference.

Not so fast there Mr. Renix!

From the 1999 FSM, and probably applicable to all OBD-II 4.0L Jeeps:


MODES OF OPERATION

As input signals to the powertrain control module (PCM) change, the PCM adjusts its response to the output devices. For example, the PCM must calculate different injector pulse width and ignition timing for idle than it does for wide open throttle (WOT). The PCM will operate in two different modes: Open Loop and Closed Loop.

During Open Loop modes, the powertrain control module (PCM) receives input signals and responds only according to preset PCM programming. Input from the oxygen (O2S) sensors is not monitored during Open Loop modes.

During Closed Loop modes, the PCM will monitor the oxygen (O2S) sensors input. This input indicates to the PCM whether or not the calculated injector pulse width results in the ideal air-fuel ratio. This ratio is 14.7 parts air-to-1 part fuel. By monitoring the exhaust oxygen content through the O2S sensor, the PCM can fine tune the injector pulse width. This is done to achieve optimum fuel economy combined with low emission engine performance.


Open Loop Modes:

IGNITION SWITCH (KEY-ON) MODE

ENGINE START-UP MODE

ENGINE WARM-UP MODE

ACCELERATION MODE (based on MAP or TPS)

DECELERATION MODE (ignores O2S input and will cut off fuel as appropriate)

WIDE OPEN THROTTLE MODE


Closed Loop Modes:

IDLE MODE

CRUISE MODE (FSM just says "cruising speed")


It should be noted that in addition to the O2 input, Closed Loop modes and also use spark advance. WOT is the only Open Loop that will advance the spark.

 

But it's acceleration based on MAP or TPS. Not just a pre-programmed mode because fo acceleration.

 

Oh, my mistake.

Tires metrick size but measure 34" in height and 11 width. Gear 4.11
The bigest gas mileage improvement was when I switched the gears then full flow exhaust/intake than keeping up the RPM. (hard not to shift up sooner with that much power on demand)

I do a lot of towing and the mileage goes down to about 15mpg. My loaded trailer weight 7000lbs and its a 3 hour drive loaded then return. Every weekend. (I know its heavy. put ceramic brakes in front and disks in rear. Best mod ever)
Dont need to tell me its to much for the truck. Safety is all about speed for load and conditions. and breaking power. been doing it for 3 years regularly without issues.

 

Now that I think about it, this probably a factor in increased fuel economy after regearing when running large tires. The FSM does not state that the VSS is consulted to determine that the vehicle is accelerating