My experience with trucks with no bedcovers is limited to Ford trucks made prior to 1990, the newer ones may be different. In an 87 long bed Ford truck, dump a few shovels of dry loose dirt in the bed, in front of the tailgate, and watch the result.
A stagnet bubble of air? Not in my experience, more like a hurricane blowing that dirt up towards the cab.

 

What tires and tranny do you have? It makes a difference. With my E4OD and 30" tires I'm almost exactly at my 2000 RPM torque peak at 65 MPH in OD using 3.73 gears. With an M5OD and stock tires I'd be pulling 2335 RPM, way too much for my purposes.

My truck originally had 3.08 gears. It gave 19 MPG highway, now I get about 16.

 

Steell's right, and in a short bed, the "dirt experiment" is just as bad. I've had both beds, and with the tailgate up you end up strewing trash and dirt everywhere. Designed for a bubble, maybe, but in practice, no way.

 

quote from http://www.awtrucks.com/tailgateup.htm

"This ran counter to their intuition (and yours). The reason is that a closed tailgate sets up a large "bubble" of stagnant air that slowly circulates around the bed of the truck (we aero types call this a ("separated bubble"). When air approaches the truck, it "sees" the bubble as part of the truck. So to the air, the truck looks like it has a nice, flat covering over the bed, and the air doesn't "slam" into the vertical tailgate.

If the tailgate is open, or replaced by one of those "air gate" nets, however, that nice, separate bubble in the truck bed does not form (it "bursts").

Then the air approaching the truck "sees" a truck with a flat bed on the back of a tall cab. This is a very nonaerodynamc shape with a very LARGE drag.

So, believe it or not, it's best for gas mileage to keep the tailgate CLOSED. Hope this information is helpful."

Ed Fitzgerald
Research Assistant
Department of Aero/Mechanical Engineering
University of Notre Dame





this is an Aero/Mechanical Engineer. not some guy w/a shovel and some dirt. that hurricane of dirt you guys see is the air bubble. the air swirls around. all the dirt test proves is that the air moves. it shows nothing about drag. you need a wind tunnel to show that. the most aerodynamic position is w/the tailgate up. its all about DRAG. you cant see drag. if you dont know what drag is here's a site http://www.lerc.nasa.gov/WWW/K-12/airplane/drag1.html. saying the truck is more aerodynamic w/the tailgate down is like saying the earth is the center of the solar system. it is proven and cant be argued against. i have provided a number of facts to prove this and you all believe the guy w/the shovel. i could go on, but i feel i'm wasting my time here.

 

But what does the introduction of a 2' wide toolbox across the width of the bed sitting 8" above the rails do to this bubble? I don't have access to wind tunnels and drag tests. I live in the real world, and without the tailgate, I get 2 mpg better fuel mileage. I have a B.A. in Mathematics, and I know how to multiply and divide.

 

Ya removing the tailgate and popping on a net is the worst thing you can do for milage right next to completely removing the tailgate.

I lost a little over 1mpg running without my tailgate, 1/2 mpg loss with it down and picked up almost 2mpg when I had my soft top bed cover. I tried all this after I saw a website that did a windtunel test on a Dodge Ram.


But in response to your original post:
Remove the MAF meter, get some carb cleaner and a q-tip, you will need to be extremely careful with the q-tip in the meter because there's 2 tiny wires almost as thin as a piece of hair, if you seen any oil that the carb cleaner isn't getting off around that area use the q-tip to help assist with cleaning it.

After that to get rid of that engine light turn on your headlights and disconnect the negative battery terminal, after 10 minutes reconnect the battery, turn off the headlights and drive it kinda on the hard side for the first few miles.....what this all does is puts the computer through a reset and relearn process.

If the engine light comes back on take it some where to have the computer ran for codes. (AutoZone does it for free)

I have a '96 4.9L 5spd with 3:31 gears and 31" tall tires and I'm at about 17mpg (I could probably get 20 if I drove normal), I was at around 11mpg for a while before I added electric fans, K&N FIPK, and had my exhaust completely redone....I had both cats removed, added a Catco #9513 highflow cat followed by a Gibson SuperTruck exhaust.

 

Unfortunately, I don't spend much time driving in wind tunnels under controlled conditions in the exact year and model truck that was tested.

There is to much difference between a Subaru Brat and an 87 F150 long bed (as an example), to make such a generalized statement valid.

I don't know what year and model of truck, and under what conditions, the test was conducted.
The articles you linked were woefully short on details. I drove 500 miles, one way, in an 87 F150 4.9L long bed. Drove 250 miles on the first tank with tailgate up, on the front tank, drove the last 250 miles with the tailgate down on the rear tank. 2 mpg better with the tailgate down.
YMMV.

 

THANK YOU!! I'm glad somebody knows what I'm talking about. Maybe SOME trucks get better mileage with the gate down, but from experience, mine ain't one of 'em.

 

Not trying to be a smart ars but you do know the tanks are different sizes, right?

 

you should always do tests on both tanks at once. and also for a few tanks. just comparing a 200 mile drive down the road isn't enough. there are too many factors that affect everything. it would be more accurate if you drove maybe 1000 mikel each try.


keep in mind that if somehow defied the laws of physics and got better gas mileage w/the gate off, its bad for the siderails and looks junky. its even worse if you leave the tailgate on and just keep it down. its not made to be bouncing up and down thousands of times every time you drive.

 

Kinda hard to use both tanks at once
Same day, same weather conditions, same road conditions, same driver, same speeds, etc. I seldomly make long trips, so I leave my tailgate in the up position. I would not leave it down all the time, because IMHO, it is bad for the bed and the tailgate. If I was driving 120 miles a day, I would take the tailgate off and put a bar across, locked into the tailgate latchs to strengthen the bed.
My test was simply to satisfy my curiosity on the effect of the tailgate on my truck, and does not necessarily apply to any others.
Like I said YMMV.

And, yes I know the front and rear tanks are different sizes, and I don't run them dry.

 

thats a good idea. keep everything nice and stiff.

 

Want to increase air flow? Port youre head around 1.94 intake, 1.60 exhaust increase youre valve lift & diration with a nice little cam, h-260 ought to do it. Now the the increased avilable air supply allowed by youre k&N filter might be justified. Ok we have Fuel, Air, whats next? SPARK !!!! MSD 6-A ignition. more air, more fuel, greater spark energy, BIGGER BANG

JMAX13...

Opps almost forgot, do not follow the instructions for oiling youre K&N filter the more you use the more money they make

clean and let air dry if time permits, then lightly mist the filter as if you were spray painting it, let it sit bout 20 min. then re-apply to any light or white filter media. Let stand 20 min or so, wipe excess, install youre now MAF freindly air filter