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Discussion Starter #1
Just filled the tank again and my milage is really sucking. I have justified it by saying my driving style is bad or whatever, but Im still getting around 17MPG mixed city and Highway. My gears are 2.73 with 31" tires and with OD Im still thinking this is too far down on the fuel consumption curves.

Anybody else has any cheaper Ideas?

thanks...
 

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Maybe you aren't high enough in the rpm's to make the engine work easier.You didn't say what you have the diesel in.....or what shape the engine is really in: have you adjusted the valves to spec,or checked timing??Is the turbo working properly,do you see smoke,what color if so? What about filters??? Do you smell fuel,or have checked for leaks? And,it seems the newer fuel doesn't get the MPG's that off road fuel does.
 

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Discussion Starter #3
Damn, I thought we were closer than that,, It in an 1986 Grand Wagoneer. I havent adjusted anything. Its just as I picked it up, probably wouldnt hurt to check a few things huh? I agree about the gears and lugging of teh engine. I just dont want to have to change all that....but not good for a dollar to wait on a dime i guess.

No Smoke, Maybe a little black on the acceleration, and you can hear a little turbo whisle so i assume its working, I have no guages on the fancy stuff so I really dont know what the engine is doing. No Fuel Leaks that i can see or smell.

You didn't say what you have the diesel in......
 

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I had 3.08's, 31" tires and 27% OD. It was geared too high. I switched to 3.73's. It is MUCH more pleasant to drive, EGTs are way down and mileage hasn't dropped noticeably. Even on the highway, when you would think you want as low the RPMs as you can get them, running at 2000RPM works great for me. I never need to downshift unless traffic slows me down. I still get 23-24MPG.
 

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Your poor mileage and quite possibly performance may be directly related to your injection pump. I have never seen a Injection pump on a take out engine that was not molested. Everyone and their brother think they can just crank adjustments on the injector pump and be right. You can not. All 6 of my B3.9's had molested Injector Pumps. Fundamentally part of all my truck builds, is to take the Injection Pump to a diesel injection service company. They go thru the pump and set it up on their flow bench to the proper specs for the CPL engine its off of. All 6 pumps I took over the years were screwed up. No way anyone can set up a IP other than on a flow bench. Maybe thats why my mileage on my trucks is so good.

Paul
 

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So Paul what is your mileage.. What gears tires and trans & body weight.. I'm kind of like Thinder .I've only ran one tank in mine so far but man was the mileage bad... 72 Bronco NP435 3:55 & 285/r16's.
..Mine sounds good but really blows black smoke when you floor it .. You can feel and hear the turbo kick in.
....I do have a 2nd Injection Pump that I've already sent to the rebuild shop and had him check it out ..It's ready to go ..I thought I'd have to put it on to get mine going But it started right up and has ran fine other than the mileage..But mine is like on a permanent trail ride ..Idling in pasture..
....I was judging my mileage at from 7 to 10 mpg.
....Want some of that!!!
 

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So Paul what is your mileage.. What gears tires and trans & body weight.. I'm kind of like Thinder .I've only ran one tank in mine so far but man was the mileage bad... 72 Bronco NP435 3:55 & 285/r16's.
..Mine sounds good but really blows black smoke when you floor it .. You can feel and hear the turbo kick in.
....I do have a 2nd Injection Pump that I've already sent to the rebuild shop and had him check it out ..It's ready to go ..I thought I'd have to put it on to get mine going But it started right up and has ran fine other than the mileage..But mine is like on a permanent trail ride ..Idling in pasture..
....I was judging my mileage at from 7 to 10 mpg.
....Want some of that!!!
I am not going there again. Last time I posted was in a thread something like this. I gave all the details your asking for, Plus a 6600 pound truck over 3411 miles. I was called a liar by more than one that posted replies. You can search and find all the info.

Paul
 

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Paul is right on with his assessment of Injector Pumps,but also,gear ratio has a lot to do with poor mpg's...when I was in school,ratio was explained something like this:gears are a lot like a lever,a longer lever ( 4:10 gears) can move more load easier (less work on the engine) than a shorter lever (2:73 gears),(harder work for the engine).I noticed that you have no gauges,boost,or EGT,and that just leaves you guessing what the engine is doing.Thinder,you have no baseline to go from,so you won't know what you need, to get what you desire.If it were me,I would make every adjustment back to STOCK spec's for the CPL that you have,and go from there,and boost,and EGT monitoring is an absolute !! Then you could make your mpg's count....now,the way everything is right now,is just guessing.
 

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Discussion Starter #9
Yeah, Thats sounds like pretty solid advice. You know as soon as i get the guages, power will be on my mind.......


Paul is right on with his assessment of Injector Pumps,but also,gear ratio has a lot to do with poor mpg's...when I was in school,ratio was explained something like this:gears are a lot like a lever,a longer lever ( 4:10 gears) can move more load easier (less work on the engine) than a shorter lever (2:73 gears),(harder work for the engine).I noticed that you have no gauges,boost,or EGT,and that just leaves you guessing what the engine is doing.Thinder,you have no baseline to go from,so you won't know what you need, to get what you desire.If it were me,I would make every adjustment back to STOCK spec's for the CPL that you have,and go from there,and boost,and EGT monitoring is an absolute !! Then you could make your mpg's count....now,the way everything is right now,is just guessing.
 

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I'm playing the gear game right now. My FIAT 5 speed in my Deutz F5L 912 F150 conversion is running nice around town and on 55 mph roads. It climbs every hill in fifth gear and has a lot of acceleration. However, I wouldn't want to take it on any trips because the rpms are around 2400 (calculated) and the mileage drops severely when I get up to 70 75. I started out with 3.55's and 225 75 r15 tires and the mileage seemed better than when I went with 2.94's and 6 ply 235 75 r15 tires. I think I'm getting in the high 20's where at first it seemed ridiculously high. Now I'm seriously coinsidering dropping down to 2.47 to see if I can get it to cruise nice and easy at about 2000 rpm / 70 mph. My fifth gear is 1:1. I just got the speedometer working today and I'll follow wife to work tomorrow to calibrate against her car. Then I'll fill up again and see what the mileage is. Gearing for everything where you want it is a weird game.
 

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Might be apples n' oranges, but the best CONSISTANT mileage I ever got was 23 mpg, with a '91-1/2 (intercooled 6BT) Dodge 1 ton, 4.10 gears and a Getrag 5 speed.
It was STONE DEAD stock, never had the pump monkeyed with, stock tires, 170,000 KNOWN miles.

WORST mileage ever was 11, weighing 22,000 pounds with a 40 mph headwind, in rolling hills.
AVERAGE LOADED mileage figured to 14mpg.

Mark.
 

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The only time I've heard of an overgeared vehicle having poor fuel economy was due to it being automatic. Then it spends too much time with the torque converter unlocked and just making heat.
Is your truck automatic?

I believe Pauls fuel economy numbers, but they're higher than the rest of us for several reasons. Mainly long trip and smooth patient driving. Having fuel pumps reset with no doubt the internal pressure which dictates timing advance is also crucial.
 

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The mileage is down becuase of the gear ratio , if you keep it that way don't use OD because now your below / right @ 1400 rpm. If no OD your right @ 2000 try that and see where fuel mileage and the big difference it made.

Scott
 

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Discussion Starter #14
Yeah its an Auto OD, Ill try running around with the OD off For a couple Hundred miles

Thanks again guys!

The mileage is down becuase of the gear ratio , if you keep it that way don't use OD because now your below / right @ 1400 rpm. If no OD your right @ 2000 try that and see where fuel mileage and the big difference it made.

Scott
 

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If your outside of these rpm/mph range by much your mileage and performance will suffer.
MPH..... Desired RPM 5th
........... auto-manual
80....... 2215-2345
75....... 2075-2200
70....... 1940-2050
65....... 1800-1900
 

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I think that with any truck with a 4bt 15-25 mpg is what most would be at. I am very happy with my mileage but I am needing higher gears to get to where I want to be at.
 

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The manual will still have a problem @ 1400 no mater what , he will still have to down shift to 4th .

Scott
Possibly, my Isuzu can pull from 1400rpm without problems and it's flywheel is a lot lighter than a 4BT.
But a manual gearbox in 4th doesn't lose any efficiency. An auto which is turning slow and not locked up is a very inefficient way to move anything.
 

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We made a 2800 mile cross country trip a few weeks ago. Our fuel mileage was 25 mpg. This is a 1/2 ton short bed 2wd pu. The transmission is the stock turbo 475 with the stock chip truck converter. The rear axle ratio is 2.50. The tire size is 255/70/15 which measure about 29". Half of this trip was interstate. The other half was 2 lane highways. Interstate speeds were at or above the limit. The truck was loaded with luggage and coolers so it was pretty light. It was seeing up to 2400 rpm on the interstate which I believe is too high for good economy. On the 2 lane highways it seems to be about right. The IP has been recently rebuilt and set about 10% up. The injector tips are new and are very slightly oversized. The turbo is new with a very slightly oversized compressor wheel and a 14 cm exhaust housing. I was running Diesel Power additive for the trip.
 
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