looking for better fuel milage on 96 12v 4x4 dually. getting around 12.5mpg need better. has a k&n air filter, exhust, pretty much stock. any suggestions would be great

 

Based on your signature, the biggest hardware modification would be to get rid of the lift and big tires. You have greatly increased your windage, rolling resistance, and rotational inertia. Once that is done, you can try to decrease wind resistance more by doing things like making an air dam and taping up body seams. If you want to get involved in motor mods, a lot of people report slight mileage increases with ddp1's. Also, make sure you synthetic fluid in everything.

The cheapest way to increase mileage is to look at your driving style. Every time you brake, you are turning kinetic energy into heat so try to plan ahead so that you don't brake as much. Also, your wind resistance goes up as the square of the velocity so slowing down on the highway makes a huge difference. Try driving for a few fuel tanks at 60mph and then for a few at 75mph and look at the difference in mileage, it is scary.

 

Has your speedo been corrected for the 35" tires? You'd be around 13% slow right now if you didn't. That would put you in the 14mpg range then, which is still pretty low. Have your timing checked. Usually get some mileage gains if your timing is retarded. How many miles on your rig? Injectors could be dirty, could look at pulling them, getting them cleaned and get the pop off pressures checked.

 

sorry should of mensioned its a buddy's truck, it has no lift stock size tires and a heavy foot, we are tring to get some better mpg out of it anyway, my 95 gets 18-21 with lift, tires ,mods, and extremly heavy foot (love the smoke),we just cant get his truck to do any better, his truck is an auto. around 190,000 miles

 

were planning on putting elec fans on to help, thinking of modifing the torque plate, gaining hp is not an concern, a plus but want mpg

 

I guess if I paid more attention, I would've noticed. Is the tranny slipping while driving. Lockout engaging? Auto stuff is all voodoo to me, but I do know they will eat up mileage and power when they aren't up to par anymore.

 

Before you start going to things like electric fans, I would try to figure out why the truck is getting such low mileage to start with.

On the engine side of things, the most common problems are plugged air filters and fuel filters. Badly slipped timing is another possibility and a bad injector can do it too.

A lot of people immediately start assuming that the problem is engine related but you should be checking all of the brakes and bearings. Put your hand on the hub after driving on the highway for a bit and make sure that none are too hot.

Depending on what shape the auto tranny is in, that could really hurt the mileage.

Are there any add ons that could affect wind resistance like a camper shell or a tall cap or anything? Also, is he carrying around a lot of extra weight?

 

nothing out of the unusual in wieght, clean filters, all is good, new trans (5 times to get right) truck has always got poor mpg, he's looking to get 4 more mpg if possible, guess he just need to take it to a diesel shop and have them make the money.

 

Check your injectors to make sure theyre not tired or sooted up.
might be worthwhile to do the valve lash as well.
Check tire sizes with whats printed on the drivers side door frame. figure out the difference in mileage with that
winter blend diesel has worse mileage.
The 4x4's will get worse mileage than the 2wd ones and the older trucks seem to get crappy mileage compared to the later ones with 180 and 215 pumps.
Small upgrades could get you a mileage gain.

 

Does he have 4.10 gears? If he does 15-16mpg will be about it. I would start with valve adjustment, move timing to 15-15.5, install new injectors, check brakes and bearings, install synthetic lubes everywhere. Only after these fixes would I try a #10 or a #8 fuel plate. I got good milage stock but when I installed my #10 plate I increased milage about 2 mpg. Then I lost it again when I installed 215hp injectors and 4 in. exhaust.

 

all the above are some very good ideas don't forget about changing the overflow valve it gave me a couple more mpg when I put a new one on.

 

Good call.+1

 

If that truck has a catalitic converter You will gain 2MPH when it falls off.