Engine/Transmission (1998.5 - 2002) Crappy fuel milage

[TimWhite]

I have a 98. 5 24 valve, 3500 4X4 has 410 gears 5 speed 4inch exhaust, banks big hoss box (Cummin off), exhaust brake, and is a custom flat bed truck was ordered cab and chassis. I do alot of towing but even running empty i can rarely squeez 10 miles to the gallon 34 gallon tank getting around 240-270 to a tank. Can someone PLEASE help this stinks love the power but i know it should be getting better than this. Thanks alot i have pictures in readers rig of the truck



TimOo.

 

[CRSmith]

It could be a dirty iat or map sensor. Do you have a K&N filter?

 

[Turbo Tim 1]

I have a 2001 3500 QC 4x4 5 spd 4 inch exhaust and edge comp box and BFG MT's 255/85's (33. 2 inches) My lowest mileage ever was towing a GVW of about 16-18,000 over through Maine, New Hampshire and Vermont and I got 11. 94 mpg. My best ever is 18. 22 mpg Empty. My average since owning the truck is 15. 78 mpg. Ditto on the IAT (intake air temperature sensor), I changed mine the summer after I bought the truck and got a 2-3 mpg increase, now I just change it every year or two instead of trying to clean it. How about your lift pump pressure, is it good? A friend of mine bought a 2001 brand new and the lift pump was dead from the factory, he was getting 4-6 mpg towing to a NASCAR race down south when it was new, he went back to the dealer and said if this is the best mileage it's gonna get your getting it back. They investigated and found the bad lift pump. I'm not sure why but these things get terrible mileage with no pressure feeding the VP-44. So I would check the fuel pressure first and if thats ok change the IAT (about $30 at the dealer)

 

[barbwire]

disappointment

I have the same basic setup as you (flatbed & duals).

I have taken issue with the poor mileage aspect of this rig since I purchased it. Ie; IAT, MAP, air filters(clean), fuel filters(change), valve adjustments, tighten inter-cooler clamps,driving slow, driving fast,etc,etc. I finally admitted defeat. But as you also said, it has all the power I can use. It has never let me down in that aspect. I hate to tell you, but I think you are going to have to live with it if you want to keep it. You could probably bomb it and get 1 or 2 mpg better, but for the cost of the bombs, it would take a long time to pay for the extra fuel, that you would burn otherwise. Just my $. 02!

I think one thing that might be killing my fuel mileage, is that the flat bed that I have on mine, the headache rack sticks out 6 inches further than the cab on each side. I'm sure that does'nt do the aerodynamics any good.

 

[johncameron]

Why don't ya like the BIg Hoss box. Just baught one but don't have it installed yet. Got a good deal though!

 

[Mundgyver]

I think it would be interesting to see how much air (air bubbles) are mixed in with your fuel to the VP. I know that this will rob you of mileage and some power.

 

[barbwire]

air bubbles

My wife says I have air bubbles in my head. I thinks it's from the wine.

 

[DDT]

barbwire,

I will agree. When I put mine on I lost 1 1/2 MPG. With tool boxes in front of the rear tires driving on side roads there is a swrill in the dust that goes 5' to 6' each side of the truck. I do have air noise in a head wind that comes from the headache rack being so tall as well, this will get lowered some day. The regular bed never did this.

 

[Theconcreteguy]

Originally posted by TimWhite

I have a 98. 5 24 valve, 3500 4X4 has 410 gears 5 speed 4inch exhaust, banks big hoss box (Cummin off), exhaust brake, and is a custom flat bed truck was ordered cab and chassis. I do alot of towing but even running empty i can rarely squeez 10 miles to the gallon 34 gallon tank getting around 240-270 to a tank. Can someone PLEASE help this stinks love the power but i know it should be getting better than this. Thanks alot i have pictures in readers rig of the truck



TimOo.

on a bad week i avrg 11. 8 ( worst yet) if i drive like im not havin

fun i get 16. 8(my best)... ... ..... if i let my old ladie driveshe gets in the high 17's !!! in town..... Oo. Oo. Oo. Oo. :--)

 

[dvaughan]

Fuel Mileage

Tim, how much weight are you hauling? I installed an Edge box for towing and I lost about 2mpg when I am not towing. Also your 410 diffs are killing your fuel mileage. Like someone else said you have to keep your fuel filter clean(change ever other oil change) and I clean my AIT sensor myself with brake cleaner(about every 12,000 miles) and it does make a differance. Also I run a AFE Megga Cannon air filter(let it breath) and clean it when it gets dirty. Also check your fuel pump, I installed a pusher pump as my pressure was poor. If you are not towing very heavy loads I would take your Banks Box off, but I think your 410 ratio doesn't help. Do you use a fuel additive, I use LubeTec fuel additives and it seems to help mileage and has other benefits.

 

[2ndgen2500]

wow, i got 19. 7 mpg today on a 600 mile trip... that really sucks about your mileage. . i have no advice accept if it was me id put a filter in, and take that banks box off, check your sensors and try again...

 

[DLBurns]

Lousy mileage

Just got back from a couple of days at Disneyland, on the way down I got about 13 mpg and on the way home it was almost 16 I have never got the mileage that some are getting, I know the 4:10's, duals, auto and 4X4 are robbing me of mileage but I thought I would see better than 16mpg

Still love this truck

 

[WLoewenhagen]

The 4. 10 gears are the culprit here. I had gas engines with 4. 10 gears before the cummins and averaged 8 empty and 6 mph loaded. With the 1st Cummins I got about 10 to 12. My current truck, A199 Quad Cab Cummins, 4x4 has 355 gears and gets all around about 16 mph. Follow the suggestions for fuel filtes etc, but without a gear change, it is probably close to your optimum mileage.

 

[ffken]

whats the gear change gonna cost if i trade gears with another fella?

 

[JFinke]

About 300. 00 and a good days work for both rigs if you do it yourself with new bearings. I always change bearings when a diff is out. You can do it for 100. 00 if you just change seals and oil. If both trucks are the same and you have never set a ring and pinion up I would just swap the housings from truck to truck. Rear ends can be swapped as fast or faster than doing the gears. The front will take as long and will need an allighnment.