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low fuel milage

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pavo

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Jun 16, 2002
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Denver, CO
I've never had better than about 18 MPG, on the interstate i get about 16-17. my machine is a 82 k5, with 31's and 3.42s 700r4 . i used to have a 84 an that thing never got worse than 20. i drive pretty conservative most of the time. I have checked all the things the diesel page says to check including replacing both fuel filters, air filter. lift pump. different fuels. My truck SEEMS to have pretty good power, but i can't drive much over 75 all the time. tranny is not slipping. whats the next step? keep driving and ignore it? any ideas? compression test? POP Test?
 
Hmmmmmmmmm.........How many miles are on the motor? When's the last time you did you did your injectors and had your timing set on your injection pump?
 
1982 134,000 miles, timing was just set, and i don't know on the injectors. how much do those puppies cost? i might pick up a few ( or 8)
 
Throw some 3.73's in there and it should help. Your engine is lugging most of the time. 31's aren't too bad, but your mileage would be better with the proper ratio.
 
Jeffro has a point about your gearing, but I doubt that's the only factor that's causing such poor mileage.

I notice that you haven't filled in your location in your profile. Depending on where you live, injectors will probably run you $50-$80 a piece. The bonus is that they are cake to install and some places have a pretty good core return on them.

It may be worth your while in the long run to spend the cash on parts if it's gonna save you money on fuel.
 
can i install the 3.73 with little effort? ive got no place to work on my truck right now, and i hate bugging my boss every time i have to do some lengthy repair
 
Nope......Unfortunately, installing a ring and pinion isn't a DIY job unless you REALLY know what you're doing. If you really want to change your gearing, you're better off finding an axle(may as well upgrade to a 12 bolt - I assume you have 10 bolt axles) with the gears you want. Just remember that both front and rear axles have to have the same gearing, so if you put 3.73s in the rear diff, you'll have to do the same in the front diff.
 
Danno on here has 3.42s and gets great milage with 31s also, so it must be something else. I have a spare injector pump, lines and injectors if your interested. Cant remember if 82' had course or fine thread injectors. Are you sure you dont have 234,000 miles?
 
i'm pretty sure its 134,000 i really have no way of telling though. i was just trusting the people i bought it from. got all the recipts for everything that was done on the thing though. some of those have milage on them and they are in the 100's. what are you asking for the lines/injectors/pump? also, is a compression test a good idea?
 
One must also factor in the oversize of the tires into the mileage calculation. For example, if the circumference of the tires are 10% larger than stock then you multiply the odometer/fuel by 1.1. If you figure 15mpg based on the odometer reading the actual mileage would be 16.5mpg. If you get pulled over, however, do not share this knowledge with the law enforcement agent. It got me out of a ticket once. "Are you telling me that I was really going 63?! My speedo said 55, I swear!"
 
actually my spedo is FAST 4-5 mph at 65 (i checked it with GPS) meaning i actually get slightly worse milage than what i calculate. i set it up to be about on with 33's which i haven't got yet.
 
I'm having a very simular problem... I used to get 22-24 mpg when I had 3:73 and 31" tires(stock Setup!) I did a 3/4ton axle swap and put 4:10 in, calculated what size tires would equivalate too roughly the same ratio and came up with slightly under 34"... I'm running true 33s now! But now I only get 15 mpg!!!??? What gives? I'm talking night and day change over the weekend it took to swap it all out! ANYWAYS!! I'm not trying to take over your post, just very curious to see what everyone has to say! /forums/images/icons/cool.gif
 
If it makes you feel any better I've NEVER been able to do any better than about 19 mpg. Most of the time I get about 16 - 18 mpg. Even when the truck was practically new (< 50k miles) my dad got about the same mileage with this truck, maybe 1 or 2 mpg better. I've changed everything, the pump, the injectors, I've even added a turbo and swaped in a manual transmission and my fuel mileage has hardly changed a bit. The only thing I haven't done is replace the whole engine, which has 225k miles on it now. I think some trucks just get better milage than others.
 
Oh yea mine has 217,000, I found that out through car fax. And a compression test is never a bad idea, I need to do mine cause I burn alot of oil.
 
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