Bad Gas Mileage

[RWestbrook]

I pull a 10,000 pound trailer every day. The last Two weeks my gas mileage has dropped 10 mpg to 8 mpg. Truck has 55k miles. What could be the problem?(99 24 v)

 

[Joe Mc]

Pull and clean the IAT sensor

I've seen a link not too long ago about cleaning the IAT (intake air temp) sensor. It is located way back & up high on the left (drivers side) of the engine. The mass air sensor is forward of it so dont get confused. I'm pretty sure it comes out with a 13/16 spark plug socket, 6" extension and 3/8" ratchet. Best if you put an old comforter on the radiator support/fender and lay yourself on top - Chest just touching the valve cover. You can clean it with carb or brake clean and put it back in. I'll bet you find it dirty. Don't tighten it too much and don't feel bad if it's loose when you go to remove it, it should be only snugged in place.



For more info do a search for "IAT Sensor" I believe there are ohm spec's if you wish to check it.



Good luck. LEt me know how it works out.



Joe Mc

 

[Alan Reagan]

Don't know where you are from but I've noticed here in Georgia over the past three weeks that the price of fuel has increased 6 cents per gallon and the quality of the fuel is lower. My mileage is down 1 mpg. Don't know if the refineries are dumping old fuel and starting to produce and store for winter or what, but the fuel quality is not very good right now.

 

[Okie-Go]

I also have noticed differences in mileage at places. I think the quality of the fuel is the problem. They may have had a bad batch or something.

 

[Fireman]

That explains it

About a month or so ago I noticed a consistent 1- 1 1/2 mpg decrease in fuel economy. After reading the thread on IAT sensors, I pulled mine and found it as clean as new. I checked for air leaks etc and found no reason for the loss in fuel economy. Since I live near Alan Reagan, I guess it could be the fuel, it's the best explanation I've heard to date.



Fireman

 

[Steve Campbell]

fireman 56 said "Since I live near Alan Regan, I guess it could be the fuel," Boy am I glad I don't live near Alan Regan. I want to know what it is about him that makes the fuel bad.

 

[UKRugbyman77]

Gas Mileage

Make sure you don't have a Dodge gasser, or if you're putting gas in the Cummins it probly ain't runnin too good either

Sorry, I couldn't resist

 

[Alan Reagan]

You guys are cold. Cold. I think it's a Southeast thing. Even my regular place that has the best fuel I have found is getting lower mileage. Maybe it is me.

 

[Steve Campbell]

Alan, sorry about that, but I just could not help myself. I hope you took that as a joke as I meant it.

 

[Alan Reagan]

Hey, Campbell, I'm LMAO. If that's the worst I get slammed, I'm doing allright. Now back to the mileage problem. Realizing that you've read EVERY POST EVER PRINTED AND MEMORIZED ALL THE INFO you may have missed the one a few weeks back that I posted where I tightened the intake cover to the correct torque specs on a 99 4X4. His mileage increased 1. 5 gallons immediately after I did this and cleaned the IAT sensor. The truck performance increased noticeably also. While I was at it I tightened the hose clamps and the exhaust manifold bolts. Believe me, as part of your regular maitenance on a diesel, if you don't go through and check torque on mounting bolts, you ain't doing it all. These engines have a lot of low frequency vibration and most are never checked to make sure everything is tight. Once it's done once after everything has settled and seated, things rarely ever loosen up again. Try checking those intake cover bolts. They torque to 18 ft/lbs if I'm not mistaken. Don't forget the long ones thru the grid heater.

 

[Mopar-muscle]

alan is correct about an intake gasket leak , mine ahd a piece blown out between the 2 inboard intake heater grid bolts . huge leak that killed my mileage to the tune of about 4mpg .