12.6 MPG Sucks

[dthollis]

Hello,



My '96 2500 4x4 automatic w/ 4. 10 is getting 12. 6 MPG. I do have 255/85/16 tires which raise the effective ratio to about 3. 80. About 50-50 town and highway with no load or trailer and not much idling either. I don't go over about 65 MPH on the road which shows about 1900 RPMs. The plate has been slid forward and the star wheel cranked some, but there is no large amount of black smoke. Timing has been checked and advanced to about 15 degrees. Speedometer has been corrected and is true.



This truck has never gotten good mileage in the 4 years that I have owned it. That is before or after any of the above modifications. About 17. 5 is the best empty on the road and as low as 9 or so with about 12000 lbs in tow on a flat trailer.



Would an aftermarket torque plate really help out that much?



Is this as good as it gets?



Comments and advice welcomed.



Thanks,



David

 

[Deezul1]

Dont forget to figure your tire size error on the speedo. With 4. 10s and an auto you wont get as good as the 3. 54 5spd trucks but it should be better than 12mpg. Maybe 15mpg or so.

 

[Mark_Kendrick]

Check EGTs and boost levels. . Sounds like a leak somewhere.



that thing should get 17+ when empty.

 

[R.Brooks]

Mine is having about the same problem. I usually get about 12 towing 10k, but lately, I've been lucky to get 12 empty! No changes in Boost or EGT. Any ideas are welcome.

 

[Mark_Kendrick]

you're missing 12 valves???

 

[R.Brooks]

NO!! I'm sure all 12 are still there!!!

 

[GOTSOOT]

mileage??

:--) There is something rotten in Denmark! Never heard of mileage that low on any CTD.

 

[Pthomas]

hows the valve adjustment?

the injectors?

delivery valves?

fuel quality?

afc spring original?

tire pressure?

filters etc.

i get 19 around town!

 

[M Barnett]

I knoticed the more go fast items I add, the better my mileage is. Now about 20 everyday driving. I would think you could get 16. Do you have gauges? About the only way I would know to find the problem would be to start checking everything. Aircleaner, timing, maybe its the injection pump, boost leaks, change brand of fuel.

Michael

 

[illflem]

If your trips are less than 15 miles the engine isn't warming up and your mileage will be poor.

 

[dthollis]

I do have gauges and the boost will peak at about 25. Filters are all clean and fuel comes from the truck stop. Valve adjustment checked, and tires have about 55 psi.



AFC spring is original and pump and injectors have not been off of the engine. Scheid Diesel in Effingham IL was the shop that reset the timing. They also slid the plate forward and replaced overflow(?) valve under warranty.



???



David

 

[pwknapp]

All you bragging on the 19 or so fuel mileage may not realize the loss of running 4. 10's. Mine averages 13. 8-14. 3 during the course of a work week. Worst was 6. 1 running 70 into a head wind with only an 8k load that caught a lot of wind. Best was 19. 8 running 70-75 following four big trucks from Indy to Memphis. I actually find my around town mileage a 1-1. 5 advantage over straight interstate 70-75. If I wuz bettr at mathh I wud knoe how much I spent in deezul over the last 400k , probly better I can't.



Beautiful wife(much better in math) says I should be getting 27. 5mpg with all the bombs I said would improve mileage by . 5 or 1 mpg.

 

[Pthomas]

yes 4. 10 will cause higher revs per mile esp with a small tire 32" or less.

I noticed tire pressure does help!

I run 70 up front and 80 in the rears.

there is sooooooo many possibilities. .

wind etc. dont forget the main one THE DRIVER!

 

[Todd G]

My mileage has not varied by 1 mpg since I bought the truck in '95. I still get 17 mpg average with 33" tires and all my mods. I don't believe the 4. 10's have that much to do with mileage. The auto is another story

 

[redramnc]

My stock '96 auto w/3. 54LSD running Uniroyal 10-ply 245/65/16s just got 23. 5 mpg on the run from Raleigh, NC to Newport News, VA to get the KDP done. This was 80% interstate at 75-80 mph, just me and my wife, with a vinyl tonneau cover on the bed to help the aerodynamics. Temps were in the 60s with high humidity so no AC was used.



This compares to a Florida run I made shortly after getting the truck (used) two years ago. At that point I got 20. 8 mpg running I-95 south on a 100 degree day in August. On that trip I got stuck behind two military convoys and the construction north of Savannah was stop and go. In between I ran 70-75 mph. Needless to say it was with max AC the entire way.



I have not bothered to check the mileage pulling my 28' gooseneck trailer due to short hauls. I make a 21-mile one-way traffic thrash commute to work through heavy traffic and manage to get 17-18 mpg on a regular basis. In the winter it drops to high-14s -15 mpg due to warm up.



Biggest variance I see is my right foot on the loud pedal. If I play I see it at the pump.



Sounds like something is going on to have your mileage be down like that. If anything gets identified as the culprit I would be interested to hear what it is. Good luck.

 

[Bud Fox]

your mileage doesnt suck- you just know how to do the math



I get the same as you with 3. 54- dont feel bad; that is probably as good as its gonna get.

 

[Garry Verheyden]

Try larger tires,

I have 4. 10's with 35" tires and I get 17-18 mpg. Speedo has been corrected for these tires. When I tow my 15,500# 35' fifth wheel I average 12-12. 5 mpg.

Garry.

 

[Diver-Dave]

I wouldn't worry about it too much David. I've done a lot of mods to my truck and notice that mileage depends on a lot of variables. I drive 6 miles a day stop and go traffic every day to work and never go over 40mph. It never warms up. I average about 11mpg for everyday driving since I probably get on it at least a dozen times per tank.



When I'm driving on the highway and stay under 65 and don't get on it I can get 18mpg. - But that's pretty rare.



I get 10-12mpg when towing my 12000# 5th wheel and I consider that pretty good since my truck alone weighs about 8000#.



I also realize I've traded mpg for power. I can get 0-60 in 6. 55 seconds so it's worth it. I do put out a lot of smoke!! I figure I lost about 1-1. 5mpg for the mods.



I would expect that if I had a gasser under the same conditions I could take all the above and almost cut the mileage in half. I know because I have friends with big block Chevies and Fords and they get:



7mpg in stop and go around town.

11-12mpg on the highway.

7mpg towing.



And there's Noooo way they could ever keep up with me.



'97 Driftwood 3500, 370 injectors, JRE TC, transgo shift kit, TST AFC Spring Kit, TST #5, Piers 3000 RPM GSK, 191 Delivery Valves, Timing @ 15. 5, Banks Turbo, Non-California intake. KDP stopped with CPFF jig!

 

[BillGotthelf]

As you can see from my info below I have odified my 96 4x4 somewhat. My around town mileage is about 13 because I enjoy see huge clouds of black smoke covering imported cars in the lane next to me. Its funny but towing 12,000 lbs. at 65 I get 12 miles per gallon.