90' 12V 5.9L Cummins Power & MPG
 

I have 1990 12V 5.9L Cummins and was wanting to know what I could do to increase power and get better mileage. I get about 16-18mpg in the city and maybe 21mpg on the highway. I'm new to diesels, but I've heard and read articles that you can boost power while increasing fuel economy.

What's the best way to do with with an engine like the one I have? How far can you push it? Is 30mpg highway a reasonable goal?

Thanks in advance for your help!

Michael

Do u consider 21 mpg I wish I could get 20 the best I get is about 15 to 16 I have a hard time beleiveing people when they say they get more then 20 miles a gallon because I have owned 2 of these trucks and both of them have gotten the same mpg so If u do get 21 mpg I would be happy with that if u want better mpg get a rice burner.But then its kind of hard to pull a trailer lol.:c:

Yes, I measured and got 21mpg consistently when the engine was in the Dodge. I've moved it into a 67 IHC crew cab 4X4 which is ironically lighter than the D250 was. The whole point of having a diesel engine is how easy (supposedly) they are to modify for power and fuel economy. And why not push towards 30mpg?! Fuel's not getting any cheaper. I do have a Ford Escort that is my city driver, but most of my trips in the truck are close to 1000 miles pulling a trailer. It adds up.

i get at least 20 mpg out of mine and the gears are way to low, i fugure with some better gears and a little bit of tuning 25 should be easy to get.

Im not sure if you have an auto or a rag, but I am pulling down about 18 to 20 right now and getting ready to get a goerend torque converter. The converters in these trucks are notorious for eating up power and mileage. Im hoping the 650 bucks will put me in the 23-25 range..

Here's other mechanics that factor in to my mpg: I have a 5spd OD Getrag (rebuilt); 3.54 diff gears; 3/4 ton 4X4 with NP205 trans case.

I've been reading diesel mags which suggest that different injectors and/or pumps, or enhances turbos can make a difference. It's fairly common to boost these engines to 400HP, which I don't need as much as better fuel mileage for the long trips I take.

i have got as good as 29 with mine but i usually average about 23. granted my truck only weighs 4800 pounds. Reg. cab, short bed, one ton single wheel

being that your running a rag, I would suggest either a tonneau cover for your bed or a camper shell. I have heard they improve mileage a bit. Also, a lot of guys including me add 2 stroke oil to their fuel with these old trucks. It helps my mileage a little and helps keep the injection pump well lubed. I generally dump a quart in at empty before a full tank of fuel.

Oh and another thought. The road from 160hp to 300hp is a rather easy road of simple mods and upgrades. The road to from 300hp to 400hp is a lot more difficult and pricey.

2 stroke oil what????? How does that help fuel milage honest I have never heard about that and what kind did u use???

2 stroke oil.. like for outboard motors or weedwackers or dirtbikes.. The cheapest you can find that is ashless 2 stroke. I usually pick up a couple quarts once a month from the wally world or local auto parts store. Dump a quart in before you pump at the fuel station. It helps and a bunch of guys do it out there. Even 2nd and 3rd genners.