mileage sucks

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97 3500 4x4 3:55 gears auto trans
just returned from an 1100 mile nonstop trip
4 fillup average 14. 88 mpg @ 65-70 mph
what's up? dealer did quick check up and said it was fine! it has new fuel filter and air filter in the last 5000mi. where do i start to look for problems? this truck has never gotton 20mpg empty like some guys claim but never this bad empty either.

 

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Leaks(fuel, air in system) , low fuel supply(pressure),timing, turbo/connections/hoses.

 

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Bud, welcome to the TDR. It sounds like you've discovered, "Dem winter fuel blues". Typically fuel mileage goes down a mile or two per gallon this time of year with the addition of #1 grade fuel to the diesel mix. Mileage should return to normal range in April or May.

Of course the above is assuming there's not something else going on such as Missouri Mule covered. Actually, 15mpg or so at the quoted speeds isn't bad. If you slowed down to 55/60 range (I know, not possible), you'd see some of the numbers others are getting.

 

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Driving with a heavy foot will drop your mpg more than any other single factor,accel slowly and avoid punching it. If you haven't lost your cat now's the time,a '97's cat should be on it's way to plugdom by now.

 

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Hear kitty kitty, hear kitty kitty. Figure on 2 to 2 1/2 miles per gallon better millage.

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Stephen's 1995 Dodge Cumming Automatic 3500 in Sanger CA. Pulling 35 Foot 9600 lbs 5th wheel. BD fuel plate 230HP,Air Filter Boot Removed, Vibrating Mirrors, Screaming Tubro

 

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When my cat fell off the truck and ran away my mileage jumped by about 2mpg. So rop the cat off your truck and chase it away and you'll see an improvement.

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1996 RAM2500 4x4 5. 9 Cummins w/5sp 3. 54 rearend. 8ft Diamond plow. Scotty type k&n filter. New truck bed(crunched my other one) Hope to add 4" exhaust soon. Silencer ring reinstalled Cat fell off and ran into the woods. Can still here the turbo just fine. Truck now sounds better and runs better! New linex spray on bedliner!

 

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Welcome Bud,
I'd have to agree with you; your truck should be able to deliver better fuel milage than that. BUT, consider that most owners (and past TDR mag. articles) have reported that 4wd will cost you 1 mpg, and the extra rubber on the rear axle (3500 - dually) will also cost 1 mpg. Driving 65 - 70 mph puts your motor right in "the zone", which is 1750 rpm to 1900 rpm. You didn't say if your driving was in the mountains or flatter plains, but a steady throttle up the hills lets the turbo do its thing and will improve milage. You won't slow down that much, really. Pushing down the pedal to charge up the hills is a thrill, but it costs extra fuel. Heavy traffic that forces you to speed up and slow down will also cost you some extra mpg's. Some things to check, clean, or replace might be: the screen pre-filter in the fuel warmer, the fuel return valve located on the P-7100 injection pump (if it's clogged or has a weakened spring, too much fuel will be returned to the tank and not enough will stay in the pump to be sent to the injectors. ), thermostat (are you running at optimum temp?), fan clutch (is it only slightly engaged when cold? - Note to Palm Beach FL residents: check this with engine OFF!!) Hope this helps. I'm consistantly getting 20-21 mpg with a 50-50 mix of suburban driving with short highway runs. Just got back from a 600 mile trip into the mountains, but the schedule kept me running faster than I usually go. The milage reflected that: 20. 5 mpg. On a 70 mph ave. trip 5 months ago the truck gave me 22. 5 mpg. Previous best was 23 mpg. But mine is 2wd and a 2500 model.

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95 2500 SLT, clubcab, 2wd, longbed, a/t, 3. 54, 138K miles, "all the usual refinements"

 

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I have a 96 4X4 2500 getting exactly the same mileage. Can't believe this can be considered normal for a Cummins. I have lotsa friends with 2500's and 3500's getting over 20, and they don't baby it either. I bought a video from Chryser thinking I could get some pointers. DON'T waste your money. It just refers to some expensive, magic piece of diagnostic equipment that only a Chrysler dealer will have. Planning to lose the cat, adjust the valves, check it again, and if still no better, get into advancing the pump timing. SOMETHING'S GOTTA' GIVE ! **** diesel prices are out of sight !!

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1996 2500 4X4 Auto 3. 54 gears...

 

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winter 99-00, my milage went down to 15,from 17 previous summer with 30k miles. This past june milage didnt bouce back, went with Amsoil air cleaner mileage went to 20per gal,now with recent cold spell, avg around 18 .

 

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winter 99-00, my milage went down to 15,from 17 previous summer with 30k miles. This past june milage didnt bouce back, went with Amsoil air cleaner mileage went to 20per gal,now with recent cold spell, avg around 18.

 

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I have the same configuration in a 96, I have an average of about 17 to 18 mpg. Never seen 20. With a load, its about 15 to 16 mpg.

P. S. My cat is dead. #ad


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Mark
1996 Dodge 3500, 4x4, Duel, Green and silver.

 

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My recently aquired truck gets between 19 in town and 24 hwy. I am usually gentle on the throttle and run/shift around 2000rpm.

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97 2500 4x4 3. 54 5spd, TST, 4inch exhaust, 235/85 Michelins, 23+mpg!

 

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Just an idea, have we done a valve adjustment recently? If not, it's a good place to start.

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Chris Timochko
1997 5sp 4X4, HX40, BD 4" Brake, Marine Compression, Custom Tuned Injection Pump, 370B Injection Nozzles, Delivery Valves, Governor & AFC Spring Kit, Psychotty Air, Water Injection, NOS Diesel Kit, 6" Chrome Exhaust System, No Smoke Valet Switch, McLeod Dual Disc Clutch, Mag-Hytec Rear Cover, Cummins Chrome Kit, Optima Red Tops, Hadley Bully Horns, Hurst Line Loc, Goodyear Wrangler AT/S 305/70/16s. Test mule for Auto Wurks Diesel race program

 

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Bud, One more thing you may want to look for is a broken valve spring. It's not all that uncommon and can cause poor milage and reduced power.

 

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I just got back from a trip to and back from Denver pulling a 20 foot gooseneck stock trailer(20' is inside of the trailer). I went there empty and came back with two Rocky Mountain Big Horn Sheep. I ran it 75 to 80 both ways, I also got into stop and go driving while in Denver and I got 18. 9mpg. This is on winterized fuel. #ad
#ad
Round trip was about 300 miles.

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96 2500 4X4, SC,SLT, 12 valve,lost kitty 5SP 3. 54. line-x liner All stock (for now)

[This message has been edited by ROCKYMNT (edited 11-30-2000). ]