Fuel Mileage

campNride

campNride

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Dec 22, 2008
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I know this subject has been beat up and I am not looking to hear that you get 40mpg or anything like that and that is the norm.....

My truck is a 98.5 that is basically stock. I have been getting crappy mileage for some time now which averages 11-12mpg with city driving. I have added a AFE filter, straight piped the exhaust, and just added a edge juice w/ attitude without the pump wire taped. I leave it on level 1 as I only wanted to give the truck a little pick me up when towing and hopefully gain some better mileage without killing my tranny. I just computed my last tank with a mixture of about 80 miles highway, 80 miles towing (12,000 5th wheel), and 100 miles city. I say city but it is hwy but for only 10 miles with some stop and go in it. After hand calculating the mileage and compensating for slightly bigger tires (265) I came up with 11.5 mpg. That just doesn't seem right to me. I usually run diesel additive with my fuel to hopefully keep my injectors clean and pump lubed. Do you think my injectors are slightly clogged or something to cause bad spray? Fuel pressure has always been between 12-14 and I have changed my fuel filter. I am basically at the end of my mod list as I don't have the money for upgrading the tranny which I know is next unfortunately.... Here soon I will be moving out to California towing and want the best mileage possible of course so what do you all think????

:thankyou2:
 
well it would depend on what gears your running with 4.10 and a 265 the truck wont be working very hard but with 3.54 it would strain a little more. but wire tap the injector pump use a stealth cover it will be easier on you, if you drive with common sense it wont kill your truck. see what that does to your mileage, if it doesnt help it bet your injector pump may be going out they will tend to lose mileage and hp before going all the way out. but try the wire tap before you go spending any money
 
look on the rear diff cover plate it should tell you the gear ratio, and towing that heavy is not the best way for mileage, put you will need to tap the pump and with a 3.54 gear i would stay with a 265 tire i think the truck came with 245 i belive
 
I plan on staying with the 265 tire and yes it came with the little 245 tire. I understand I am not going to get great mileage while towing but I am getting 11-12 mpg empty also. It is that way all the time..... I only tow that much once in awhile.
 
yeah that sucks for that truck unloaded, does it ever miss or act like the power just aint there, you might want someone to check for codes on that thing.
 
I have had the codes checked before wondering if it was in limp mode or something and nothing. Well I did have the death code but it was with another code that it sometimes gets thrown with it. We reset it and then nothing. I have been watching the fuel pressure for the past couple weeks since adding the edge monitor and it stays between 12-14 all the time. I will have to get the codes checked again as it has been a couple months since last checked. Seems to have plenty of power for a stock truck. Better now with the edge.... I added the filter and straight pipe exhaust in hopes to letting it breath better figuring it would get better mileage. Honestly I am "scare" at tapping the pump wire as of all the stories I have heard about the pump dying shortly after tapping. Granted I don't know all the details and they might have been really giving it a workout on level 5 in stock trim... Who knows. Just want to keep the truck as reliable as possible. Power wise I am fine with it on level 1 but the mileage sucks all the time.... Do you all think I should get the injectors pop tested? I am trying to learn here and I appreciate everyones help....
 
campNride said:
I have had the codes checked before wondering if it was in limp mode or something and nothing. Well I did have the death code but it was with another code that it sometimes gets thrown with it. We reset it and then nothing. I have been watching the fuel pressure for the past couple weeks since adding the edge monitor and it stays between 12-14 all the time. I will have to get the codes checked again as it has been a couple months since last checked. Seems to have plenty of power for a stock truck. Better now with the edge.... I added the filter and straight pipe exhaust in hopes to letting it breath better figuring it would get better mileage. Honestly I am "scare" at tapping the pump wire as of all the stories I have heard about the pump dying shortly after tapping. Granted I don't know all the details and they might have been really giving it a workout on level 5 in stock trim... Who knows. Just want to keep the truck as reliable as possible. Power wise I am fine with it on level 1 but the mileage sucks all the time.... Do you all think I should get the injectors pop tested? I am trying to learn here and I appreciate everyones help....
Click to expand...

When I had the edge comp on mine I got the best mileage on 5x5 with the wire tap. More accurately speaking, my mileage gain was minimal buuuuut it was way more consistent. More evened out between city and highway driving.
 
put the stealth cover on i just tapped my wire first beeing cheap didnt get a good connection it was like on and now on now off, i hen just brought the cover made it easy on myself never loocked back. ive had mine for 40 or 50 thousand miles last 3 years and never had a problem with the injector pump, as long as you have good fuel flow and pressure you shouldnt have a problem. the cover is a better way of taping one you dont have to tap any wires and not worry about corresition
 
Now that I mentioned that my fuel pressure was always 11-14 and very rarely it dropped to 10 psi for a split second I got on it today a couple times and initially my fuel pressure would sometimes hit 9 and then go back up. other times it would hit 10 all the other times.
 
Set your valve lash!! My buddy was getting an average of 17mpg empty and then noticed it go down to 11-12 mpg consistantly. I reset the valves and back to 17mpg.
 
If you have the shop manual or a print out from the cummins dealer it is not difficult. The first time setting the valves may take you an hour, but the next time should be able to cut that in half.
 
Street Sleeper,
Thanks for that idea. That is very similar to how my truck is because a couple years ago when I bought my truck it was getting around 16 mpg stock, but over time it had dropped. I did change tire size so at first I just chocked it up to that until I started calculating the little difference. I do have the manaul and my buddy has some experience doing that kind of stuff so I think I will look into the valve lash first. Thanks for all your opinions and experience....
 
Just wanted to give you all an update for future searchers. First off my lift pump was on the way out. It finally failed on me so I replaced it. My fuel pressure went up to about 18-19psi at idle. Next I adjusted my valve lash. They were way out.... like double the depth. The longest part about the whole job was finding tdc and now that it is marked it will be easy in the future. I have only ran a tank or two through it but the mileage has increased a couple mpg. Last weekend I towed a 3,000lb flatbed trailer with quads on it on the freeway doing 75mph and got 14.5 mpg. That is success in my books lately. I know if I was to slow down to about 65 it probably would have gotten a little better but that is good enough for me. Looking at maybe adding some small injectors next. Still wondering if all aren't spraying quite right. Thanks for all your help.
 
with my 200's a 62/71/14 I get 16 after making 12 passes at the strip in driving from redding to fortuna and back. hwy with the wife driving 18.5. Towing gooseneck with a 04 long bed crew 4x4 dodge I still got 12.5. Towing the old 30' goosneck 3 horse trailer with 2 mares and foal it got 14. it really depends on what you tow and how fast you go. average 63mph towing. But my truck has synthetics front to rear
 
Well I think I finally found my problem. I was inspecting my brakes last night before my big upcoming trip and found my front calipers dragging so bad I could barely move the wheel. I am heading down to get new calipers today and hopefully start seeing better mileage.
 
Any updates on better mileage once you got the brakes situated? How many miles are on your truck? My 99 has 201K so I need to start checking some of this stuff only getting 15mpg consistently, was getting 17mpg when I got this truck 5 months ago.
 
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