Still bad fuel milage!!!

[CCahill]

30 K miles, and the milage dropped from 16. 5-19 to 11-13. 3... ... all of a sudden.



Changed the fuel filter

Cleaned the air filter

Checked tire pressure

Changed fuel stations, at least 4 times

Havn't changed my driving habits

No winter fuel here.

Put a fuel pressure guage on it today, at idle, pre and post filter, close to the same about 11#... I could,t go down the road and test under load because the hose was too short, and my girlfriend refused to ride on the bumper...



All seriousness aside... . This is bumming me... I love this truck. . 1 reason was for the milage. .



Guess I'll be going to the dealer soon... ... don't wanna



Colin

 

[pwr2tow]

Could be the IAT (intake air temperature) sensor.

Maybe the MAP sensor.

Is the engine comeing up to operateing temp 180-190 degrees.



Ron

 

[BigDaddy]

Colin,



I agree with Ron. Check that IAT sensor. I remember Marco first bringing this to our attention. See Advanced Diesel Technology's page about IAT Problems.

 

[CCahill]

Sorry... I knew I had replaced something else... . I did replace the IAT sensor... ... ... ...



Colin

 

[GDouglas]

Try checking the intercooler connection hoses for loose clamps or damaged connectors. Seems like I read a post about one of them rubbing against a body seam and tearing at one time. Also check your turbo shaft for any loose play and look for any exhaust leaks before the turbo. Sounds like with your fuel pressure you probably have enough fuel, so maybe not enough air is going with it.



Good luck.

 

[Devildog]

Some of the guys were saying that the winter blend fuel has alot to do with poor milage.

 

[jjdiesel]

mileage

One thing that messes with mileage and is hard to detect is the auto transmission. Learned from my '99 auto diesel..... just like you, all of a sudden a solid 2 mpg drop. Engine seemed to run the same, everything seemed normal. I've got a great service manager at the local dealer, replaced a pressure sensor thats located in the transmission... . bam, just like that, mileage right back up to where it was. Of course, this only applies to automatic transmission's. If you have a hunch, I can find out exactly what the sensor is called and where its located.

 

[WTBurke]

Hey Colin



I was just in Reno yesterday Wed. the 16th and ran into Kevin Wick of Cummins Intermountain Inc. in Sparks NV. We both were grabbing lunch at a road side burger joint.



It was a pleasant conversation about TDR motor stuff. One thing he told me was to be sure to watch my fuel mileage and when it drops off get my valves adjusted.



He said under normal mileage we don't need to do this untill after 100K miles plus but stated that a lash error of 3 to 5 thous. can cause fuel mileage to suffer.



I asked if you could "hear" the differance in "sound-Clatter" and he said yes if your really in-tune with the sound of your mill.



I told him I don't want to go to my local dealer in MT or CA and he said come to Cummins it's less cost and only takes an hour.



I only have 13K miles total so it'll be awhile for me at this point but I thought this was good info from a guy that makes his living doing nothing but WORKING ON CUMMINS mills.



Hope this might help your search for the reason



Good Luck

William

 

[CCahill]

Well,

It looks like I can adjust my valves... ... see if that helps, then I can try the MAP sensor. Got my fuel pressure guage going today... at idle, it's reading 12-13 #, if I run it hard thru the gears , it doesn't drop below 5-6. I'm thinkin' thats OK. . so I can figure the Lift pump is not the problem...



thats where I am today... . still bummed



Colin

 

[DavidD]

Cahill, I noticed that you are in the foothills. I liveup in gardnerville, elev. 5K. i always notice a decress in milage when it turns cold. Not as efficent I guess. my last tank was at 15mpg. I usually get 16-17 sometimes even 18 around town. I know it has been cold here cold it be that cold where you are?

Dave

 

[azcummins]

My 98. 5 24V gets 15. 5 mpg, 2 mpg less than my 12V. It fluctuates between 15. 5 and 12... all empty. i've come to accept it as I can't figure it out. So much for the 20% increase in fuel mileage... thanks dodge...

 

[DavidD]

Mark, what is your gear ratio? I have a 2500 so I dont have duels but i have had as high *** 23. 5. We went on a Boy scout trip in 2000 to seattle and I was forced to drive the speed limit. I was with a ford V-10 crew cab and a dodge mini van I think it was a Caravan. i got better milelage than both of them. On the whole trip I got 19. 8 average! I have 3. 54's with 315-75-16 tires so my hiway cruising rpms are low. i also gotr better mpg when I installed my first fuel box which was a VA from BD. I does help and you'll have tons more fun! Dave

 

[Cummins Corvette]

That isn't way off. I only get 15 too, and I have a 12v. Just filled up today, 15. 1 mpg. I drive it really nice too, just luck of the draw. It sucks to know how to operate a calclulator correctly. I think all the guys that get the high mileage either live in their trucks and never let them stop, or don't get accurate numbers somehow. I have had two of these trucks, and they both got around 15 - 16 mpg before and after bombing.

 

[RobbyRam]

Hey dude, forget all the above comments. They are well meaning but way off target!

I went from 13 city 15 hwy. to 19 city, 24 hwy. How?

Not cheap, but not expensive, either.

I added an 'EZ', and DD II's. The increased power knocked '7 ' full secends off my '0-60' times. But my new fuel milage was a pleasant surprise. On a 500+ mile trip over the back side of the Sierras haulling a load of roofing equipment, I averaged 23 mpgs at the pump.

 

[DavidD]

CCahill, i agree with Robby, If he would look closely at my post I said i picked up mpg when I installed my first fuel box! I does help but cold air also will knock the crap out of your milage. On a trip to Utah last winter it was 0-5 above and I think I only mamged 13. Everything runs with more resistance when its cold. Good luck and try getting yourself a box you"ll love it. Dave

 

[RustyJC]

Filled up this morning - 15. 1 MPG on the last tank using manual long division! Not bad for commuting back and forth to work on secondary streets. Slightly better than my V-10 3500 got (7 MPG or less was typical for the same service).



When towing our 13,500 lb 5ver at 65-70, the EZ (with boost elbow and 4" exhaust - all installed the same weekend) was worth about 10% improvement in fuel economy. It improved to 11 MPG from 9. 5-10 MPG. This was just icing on the cake as the major improvement was in towing power - hills that were 5th gear WOT are now 6th gear @ 1/2-2/3 throttle.



Rusty

 

[pwr2tow]

I agree that adding some upgrades will benefit mileage to some degree, but if your mileage dropped that much and that fast I would fix the problem before adding any upgrades.



Ron

 

[RustyJC]

Originally posted by ronsram1999

I agree that adding some upgrades will benefit mileage to some degree, but if your mileage dropped that much and that fast I would fix the problem before adding any upgrades.

Yep, agreed.



Rusty

 

[jponder]

"26. 5! 26. 5! WOW!

Can you give us a Certified Document on your mileage... . ? Hard to belive, when most of us are getting 14. 5- 18... BTW, send me a check, I know what The Dow/Nasdaq is going to do next week... ... ... "



Maybe your attitude is coming back to haunt you.

 

[SmokinJoe]

Originally posted by CAnderson

That isn't way off. I only get 15 too, and I have a 12v. Just filled up today, 15. 1 mpg. I drive it really nice too, just luck of the draw. It sucks to know how to operate a calclulator correctly. I think all the guys that get the high mileage either live in their trucks and never let them stop, or don't get accurate numbers somehow. I have had two of these trucks, and they both got around 15 - 16 mpg before and after bombing.

I am stock, Amsiol in the enine is the only saving grace. My average for the first 11,000 miles is 16. 99 mpg and my average speed is 30 mph. I am very accurate and I use PS in every tank. Soon to have amsoil in front and rear diff and magtec covers.