Engine/Transmission (1998.5 - 2002) Lost 3 MPG Dealer has no idea

[gluther]

Hey guys I need some help. I have lost Approx. 3 mpg on the last two tanks. I only have 5300 miles on the truck. I changed the fuel filter two days ago and it looked good. Took it to the draler, they checked it and said it checked out ok and then sent me to a diesel shop. They checked the boot clamps and my fp gage. It stays around 14psi. Then he gave me some fuel treatment and said to try that for a few tanks just to rule out low grade fuel. The best milage I have ever gotten is 17. 5. Now its down as low as 14. 5. I changed the oil and fuel filter at 1300 miles and at 5200 miles.



I have a 02, 2500, HO, six speed, 4X4, ext cab, long bed, stock

 

[SmokinJoe]

Originally posted by gluther

Hey guys I need some help. I have lost Approx. 3 mpg on the last two tanks. I only have 5300 miles on the truck. I changed the fuel filter two days ago and it looked good. Took it to the draler, they checked it and said it checked out ok and then sent me to a diesel shop. They checked the boot clamps and my fp gage. It stays around 14psi. Then he gave me some fuel treatment and said to try that for a few tanks just to rule out low grade fuel. The best milage I have ever gotten is 17. 5. Now its down as low as 14. 5. I changed the oil and fuel filter at 1300 miles and at 5200 miles.



I have a 02, 2500, HO, six speed, 4X4, ext cab, long bed, stock

ait sensor? cold weather?

 

[keimmmo]

I see your truck is fairly new. Have you added any accessories like a bug deflector or topper? A number of years ago a friend bought a new 6. 2 Suburban. He was quite happy with the economy... but suddenly lost 4 mpg! After trying everything, it occured to him that the economy drop came about the time he added the bug deflector and a rear spoiler to keep the back window clean. He took them off and found his lost 4 mpg!!! He never put them back on!!!



Steve

 

[jtisdale]

Sensors, filters, fuel, and tire pressure

I would first check the Air Intake Temp sensor. While you have it out, I would clean it with an electrical contact type cleaner. Check your air filter. Have you changed fuel, or has your filling station changed the fuel without you knowing? Check tire pressure. Have you been letting it idle much? Are you making shorter trips? Has the weather been colder? Are you figuring mileage by hand at the pump, or by an overhead trip computer?

 

[gluther]

Nothing has realy changed. The truck is all stock other than the gages. I did notice the change when the guy drilled the taps for the ETG & boost. I do have some short trips but never shorter than 15 miles. Tire psi is 55 F, 45 rear. The weather is warmer. The air filter looks new. I check the milage by hand and the fuel I can't say. I am going to call the dealer Monday and see if they will change the IAT.

 

[Whitmore]

I agree, clean the IAT and also the MAP, no need to replace them just clean them.



cheers, Kevin

 

[Pit Bull]

Sounds like we have about the same mileage on our trucks. I don't think there is anything wrong with your truck. I am sure it is fuel quality and some driving condition issues. These can vary from tank to tank. Mine has 7K miles on it and I am now getting 17mpg as a rule. But it will jump around from one tank to the other. I have had a high of 20mpg and a low of 14mpg. I would do nothing for the next fourteen thousand miles and if it is not up to the 18-19 average then take it back to the dealer and check things out. Example with my 2000 CTD I had a 180 mile highway trip that I got 21 mpg going and 18 mpg coming home and the difference was now windy it was driving home (big head wind)

 

[gluther]

gluther

Well I have taken it to 3 dealers. None know what an IAT is. I ordered a new one Friday and the 18 year old service tec. said that he would change it for me Monday. I will take him the information that I have printed out from TDR to show him how. He put the computer on it Friday and the IAT was 179. The water was 190 and the EGT was 250. I spoke with a tec the other day that said that Cummins falls him for advice. He said just to drive it for another 20K miles and see how it does. I don't know if they are lazy od just don't know. Monday will tell if the IAT is dirty or not. Thanks fo rthe help.

 

[gluther]

Originally posted by RSaylor

tires really sound under inflated. is that what they recommed?

I thought that is what I saw on this site. What should they be?

 

[Pit Bull]

Re: gluther

Originally posted by gluther



Monday will tell if the IAT is dirty or not. Thanks fo rthe help.

Do you have an exhaust brake? If not there is no way your IAT is dirty on a new truck with 6K miles on it. Run 65 lbs in the fronts, on my dually I run 60 lbs in the rear, but you don't have a dually So take someone elses advise on the rears. Your truck won't be broken in until another 14K miles are put on it so wait until your at 20K miles, don't worry be happy.

 

[Camara]

Last summer I had the same problem. I was averaging 14mpg. So I called the dealer, setup an appointment and went in. My complaint was that I lost about 4 MPG. Well they said "this is a heavy truck". I had been driving it for a year as the dealer had seen it and been averaging 18 mpg. It was an all of a sudden drop. Well to make a long and argumentative story short. I have not been back to the dealer since and I still have 20,000 mi left on my warranty. I cleaned the AIT & MAP. Since then I have put on a AFE Megacannon, DDII's and a Banks computer and keep after the tires. I run 65 front and 80 rear. I am now consistently getting 19MPG. All my figures are done by hand. The gadget in the console is always off.



Good luck,

CJ

 

[NVR FNSH]

Originally posted by RSaylor

if you have ten ply, they should require 80- 85 psi. you can look on the side wall of the tire. 8 ply usually require 60-65 psi. did you go to a more aggressive tire? tire tread patterns and proper inflation can mean as much as 33% of your fuel millage.

Isn't 80-85psi for the max loaded condition? I've never run tires at what's on the sidewall when unloaded. I adjust pressure until I get an even contact patch.



Brian

 

[mberry]

NVR FNSH



I believe you are correct. I have never run my tires at 80psi unless I'm running heavy. I run 55 front, 45 rear when empty.

 

[Camara]

I forgot to mention I am always loaded and run close to 10,000 pounds. That's why I blow up the tires hard.

 

[gluther]

Re: Re: gluther

Originally posted by Pit Bull

Do you have an exhaust brake? If not there is no way your IAT is dirty on a new truck with 6K miles on it. Run 65 lbs in the fronts, on my dually I run 60 lbs in the rear, but you don't have a dually So take someone elses advise on the rears. Your truck won't be broken in until another 14K miles are put on it so wait until your at 20K miles, don't worry be happy.

I took mt truck to the dealer today and then said that they wanted to charge me to check it. I brought it home and checked it myself. ( I do not have an e-brake) and it was clean as a new one. I filled up today and the mpg is back up to 15. 8 w/fuel treatment. I will change my tire psi and see what that does Thanks.

 

[AMF]

acuse me. what do you think that diesel weighs? your front end is loaded. true you dont want to carry as much on the rear if you run empty a lot. however i still run mine up a little and rotate more often to gain even and optimum tire life. fyjimo

 

[gluther]

Originally posted by RSaylor

acuse me. what do you think that diesel weighs? your front end is loaded. true you dont want to carry as much on the rear if you run empty a lot. however i still run my up a little and rotate more often to gain even and optimum tire life. fyjimo

You are right. I am going to raise the psi a bit and see if that helps. It may help with the stiffness in the front end as well. I run empty all the time. I have a fleet of trucks that I drive for work. I don't have a lot of time to drive this one. I hope to get it loaded up before long just to see how it pulls. Thanks.

 

[TBarrett]

mileage !!

on my 01 I get 18. 2 generally. I run 65 front and 40 rear for air. I didnt check the air for awhile and fueled up and was at 17 mpg. I checked the fronts and were down to 50 psi. So, air is important. Out Reno way I got 1. 5 less during the winter months. But now its at 18 and alittle all the time. I'm at 22000 miles now. I have talked to others and they state that at 45000 to 50000 I should get a 3 to 4 mile jump. Thats great but they didnt know why ????. I have a shell on and if you dont tailgate up or down makes a difference, Air flow, I was told.

 

[plongson]

IAT was clean...

Don't be in such a rush to check the IAT unless you really think there is a problem (or you have time on your hands)... Reading all the links and info on dirty sensors, I thought I should check before this weekend roadtrip. It was absolutly as clean as new and the truck has 53,000 miles. Glad I know the condition though, sprayed it with carb. cleaner and reinstalled. Total time, about 45 min.

 

[speedracer]

TBarrett, I wouldn't be holding my breath on that 3-4mpg improvement at 45-50k. I'm at 55k and have seen no such sudden(or otherwise) mpg jump. I wouldn't have expected one either, there's no reason for it.