Fuel economy.

[pybyr]

On the original poster's question-- I would suggest that, based on my experience, my truck so far does not have the upside of upper MPG that I have been hoping to find

(but then again, it is a 1 ton with 4x4, a huge toolbox work body, DRW, and big mirrors, so the MPG that it gets- reliably 14 to 15-- is pretty amazing- I might as well be driving a small barn down the road in terms of the profile I cut through the air)

but it also, unlike any gas vehicle that I've driven, or my Cummins common rail, my IDI has the advantage of being willing and able to work itself to the bone without any DROP- none whatsoever- in mpg in my experience. Sending this massive truck hurtling full tilt up some very steep and long VT hills with a mess of stuff in the bed and still getting 14.38 MPG is enough to put a grin on my face.

and oh yeah- I have a 4.10 axle ratio. When you consider that- and the other things I mentioned above, the fact that I've never gotten under 14 mpg is pretty wonderfully miraculous.

 

[The Warden]

For guys like me who want to maximize MPG, and I generally don't need a ton of power-- would turning my pump down a bit beneath stock go anything-- or, I assume, I'd get the same results by "staying out of the pedal" a bit more?

I don't think turning down your pump will gain you anything that keeping your foot off the pedal won't gain you. And, for that matter, I don't think keeping a pump turned up will automatically lower your fuel economy...the real question is how heavy you are with your foot. If you have the pump turned up but have a habit of feathering the pedal on a regular basis, I'm pretty sure your economy will remain about the same.

I really want to get my hands on a Moose Pump someday, when finances allow...more power when needed, and I think a more efficient burn (i.e. better fuel economy) for driving around. I'm generally pretty light on the pedal, although I'd like to have the extra power available when needed...

FWIW I average between 16 and 18 mpg with my truck when either empty or under a light load...for a 4x4 with 4.10's, a lumber rack, a pump turned up 1/2 a turn, and weighing in at right around 7K lbs, that's not bad at all IMHO. And, I once did a run down to L.A. with an empty truck and the cruise set at 55 indicated (later found out that 55 indicated is 50 actual on my truck, courtesy of my GPS)...got 20 mpg going both ways so, speed makes a difference also. I can't wait to see what an intercooler and my OD unit will do for economy I just wish I could pull the lumber rack off and store it somewhere...

 

[jam sandwich]

I just did a first mpg calculation on my newly acquired 89 f250 IDI.

Between a mix of city and hwy I got 16mpg.. not too bad considering the injector lines are leaking, and the timing hasnt been set (its still at the factory mark)

All in all, I was pleased with that result. A little more tooling around and I'll be close to 20mpg!

 

[The Warden]

I just did a first mpg calculation on my newly acquired 89 f250 IDI.

Between a mix of city and hwy I got 16mpg.. not too bad considering the injector lines are leaking, and the timing hasnt been set (its still at the factory mark)

All in all, I was pleased with that result. A little more tooling around and I'll be close to 20mpg!

Doesn't sound too bad at all!! What tranny and differential gears do you have? 4x2 or 4x4? Are the tires and suspension stock? ...those factors can make a big difference in fuel economy...

 

[jam sandwich]

its a 4x2, with a 4.10 rear end.. I usually go around 65 on the hwy (2500 rpm)
The truck is really rough (its ugly as hell) it leaks oil out of the valve covers and rear main seal, has a coolant leak somewhere, the a/c works (barely) and as I mentioned already, its leaking diesel out of the return lines.. quite a bit I might add, you can see fresh diesel dripping from the rear of the engine.

Got 189k on it..

 

[Clydesdale]

The leak is 9/10th of It I would wager. My last IDI, factury Turbo CC 7.3 ZF truck, 4x4 4.10 gears.. did a pretty consistent 14-16, lower towing hard, not much better than 16 ever. I finally buttoned up exhaust at the Y for the turbo, and slowed the fuel leaks down to a weaping moisty kinda deal, and picked up 4 mpg at 65 mph form 3k elevation to a high of almost 5, to its home turf of 2500. had an empty 18' trailer for the first half, and empty empty for the last half.

 

[Clydesdale]

oh and i was 300k miles on the odo, with a non turned up 6.9 IP

this set up got me 13-14 with leaks.. and a shot IP...

You must be registered for see images attach

 

[burtcheca]

Do you, guys, think that using the cruise control at 55 or 60 on the highway saves fuel? Will it be better not using it and going at the same speed but without the sudden accelerations you notice sometimes with the cruise control on?

Burt.

 

[Clydesdale]

that could be argued all day. but since mpg realies on law of averages, I would say no.

I have seen 8.1 vortecs do 50 + mpg..
























then the accelerator was depressed again.

But for that brief moment in time it truly did 57 mpg.

 

[NapaBavarian]

My t19 with 4.11s in a crew cab dualie got me 14 despite every ones warnings of the t19 4.11 combination, auto will take some fuel to run, my duramax only does about 1-2 mpg better even with 3.73s and overdrive so I'm going back to IDI

 

[matt-jenkins]

Yeah somethings not right there. Are your fuel injectors painted grey? If so that means they are original from factory and well beyond their service life. Even if not, you might still consider having the injectors pop tested by a diesel injection shop. The shop in my town does this for free, not sure about others.

Having the fuel turned up isn't helping but its hard to say if thats playing such a big role here. If you keep an eye on your side mirror, are you seeing any smoke when you are up at cruising speed?

I'll go check my injectors later when I go out to my truck I believe they might actually be grey...

The only time I see smoke is a puff on start up and when I have my foot to the floor, I try real hard to keep it smokeless while daily driving.

 

[pybyr]

What do you folks think is the happy RPM band for a N/A 7.3 IDI to keep it in the sweet spot for MPG? My E4OD plus 4.10s lets me keep not-too high RPMs on the highway- but I am wondering where to expect the real fall-off on MPG so that I can keep it below that. Perhaps its the same general area where MPG drops off anyway due to the fact that wind drag increases geometrically and really hits hard at over about 60?

 

[david85]

In general you want to keep it at or below 2000 RPM. Although there have been rare exceptions that get acceptable MPGs even with low gearing, that was under 60 MPH if I remember right though.

Cruise speed matters a lot too. I can average around 20 MPG on a good day@ 70 MPH, but if I drop to 55 MPH, I gain 4 MPG.

And then it also varies by region depending on what sort of hills you are up against in an average driving cycle.

Matt, I think your injector set has paid for itself by now if they are indeed original. Generally they should be replaced around 160 000km

 

[The Warden]

My t19 with 4.11s in a crew cab dualie got me 14 despite every ones warnings of the t19 4.11 combination

That's about what my truck got when it still had the T-19 and before I added the turbo. I got 14 to 15 at first, then it dropped to 11 to 13 after I got the turbo (I think I played with the go pedal more than I should have ), then jumped to where it is now after I got the ZF in. Granted my truck isn't a dualie nor a crew-cab, but it IS a 4x4...

 

[matt-jenkins]

So, this fill up I got 300km to the tank, 60 less then i got when I calculated it last time. Im also getting hard starts as well, I think it is time for a new fuel system.
Pensicola diesel seems to have the best price on a reman pump and injectors. I'm N/A so i dont care about getting performance parts but is there stuff usually pretty good? Anyplace else i should look besides moose products?