2 questions: fuel mileage and overdrive
 

i just added a 93 D350 automatic dually to the diesel collection (my first-first gen.). what controls the OD? it seems to shift in and out at will. sometimes flat road or downhill without adding throttle. The second question is what mileage can i expect? first tank is about 19 mpg with very easy driving, not above 60. i have a 130 mile commute to work and would like the best mileage i can get. i dont know if it has any mods other than no intake system, just a filter on the front of the turbo. thanks in advance for any help.

vehicle speed sensor and throttle position sensor determine OD. Throttle sensors are around $300 if i remember right so people buy the cheap potentiometer like it have for $30. I get around 22 in the city with my 250 auto and thats not stock. I have never checked it on the highway since i usually go around 80.

Gearing is a BIG factor on them, but so is how it's loaded.
I've gotten my BEST average MPG with a 4.10s and a 5 speed on a '91.5 intercooled truck.
It was also my best AVERAGE MPG in one of these trucks, loaded or otherwise.

If you don't plan to load it heavy all the time, 3.54s will do really well, as will 3.07s, but the 3.07s would be best with a 6 speed, IF you plan to pull a heavy load some of the time.

My old carhauler has 4.56s with an NV4500, tops out at 82 mph in overdrive, and gets between 11 and 15mpg, averages 13.
It weighs 9,000 pounds empty, and has scaled, as a single unit, over 17,000 pounds with a fully dressed E/C Dually 4x4 Cummins truck on it's back.

The truck I'm referring to is pictured below:
http://img.villagephotos.com/p/2010-...DSCI0001_2.JPG

id love a 6 or 5 speed but i really dont think i will make the conversion yet. this is my first auto truck. do you recomend ring and pinion then? i have heard of a double overdrive but dont know anything about it. i dont pull often nor do i pull real heavy. (allis chalmers d17, a few cars and a 20 foot alum. boat) a few times a year. mainly this is for commuting. is there a good place to start on the timing for best economy? im installing 4 inch exhaust tomorrow. im going just past the cab with a turndown. cold air intake to follow. right now i have a spectra filter on the front of the turbo. thanks for the help so far.

19 with an auto ain't nothing to sneeze at.

My 1 ton im my signature has 3.54s and an auto.
The very BEST it has gotten is 17mpg and it averages 16mpg, best I can figure.
It'll smoke like a smothered stove, unless you ease into it, but the turbo clears it if you mash it and let it spool.

Do NOT go overboard on advancing the pump timing, if anything, give it an 1/8"-1/4" bump and put thinner washers under the injectors, to help alleviate any possibility of the injector spray getting outside the bowls.

While it has some good theory, the idea of super-overdriving these engines is destructive, unless you are using some heavy-duty parts AND you are turning out some serious torque.
For the most part, the people who engineered these trucks knew what the components could and couldn't take.
If you think about it, if it was such a good thing, why didn't Dodge offer (without special ordering it) a 5 speed with 3.07 gears?

Probably because the combo would likely not make it long enough to satisfy the warranty period, AND it's a poor towing set-up.

Mark.

i guess i need to see what gears are in it. i am runnin about 2000 rpms at 60 but id like to run at least 70 on the interstate at 2000 rpms or less. id prefer 1800 or less!120 miles of the 130 trek is on interstate. i have another truck for pullin so i dont need raw power but dont want a dog either.

hey kieron is there a way to test the throttle position sensor? if the speed control sensor was bad would the speedo work? sorry to keep askin... im just tryin to get this on the road again.

The speedo won't work if the speed sensor is bad, that's it's primary designed function.

If the speedo fluctuates or goes dead, then comes back, I'd suspect the wiring before the sensor, but the speed sensor can go finky like that.
If the speed is steady and no fluctuating, the speed sensor is likely fine.

Testing the function of the TPS is as simple as using an OHM meter on two of the pins to check for continuity throughout the range of motion.
If it reads '0' in any portion of the range, the TPS is bad.

I can't recall exactly which 2 pins to hook to. :humm:

As Kieron mentioned, the potentiometer fix is a good option to the nearly impossible to find and overpriced TPS, but it takes some getting used to, as you have to adjust it manually to your driving habits.

Mark.

Hi Mark, Richard here...followup question pleae...and thanks. Same TPS problem...cking it Monday...is there a "factory setting" for the TPS? Or...does one just experiment accordingly until ? I am towing HEAVY on a new job and can't hit the road until my OD problem is fixed... thanks again and to anyone else.

Happy New Year to everyone TOO!

The TPS should be adjusted at idle, engine off.
The TPS has a hex head that mates into the throttle arm retaining nut on the injection pump, this should be adjusted so that the hex head sits straight down into the nut, with no re-indexing to get it to completely seat down.

IT CAN BE TRICKY TO GET IT RIGHT.

BEFORE you adjust the TPS, you need to make sure the throttle settings and the TV cable (AKA "Kickdown") settings are correctly done, THEN adjust the TPS accordingly.

Keep in mind that every time you do an adjustment on the pump that affects idle position, or if you remove the throttle arm for any reason, you "should" check and correct the "at rest" position on the TPS.

Another way to adjust it is by minimum and maximum resistance values, which I believe are in the Dodge FSM, along with the procedure they recommend.

I use the "At Rest" method, because it works well for me.

Mark.