Engine/Transmission (1998.5 - 2002) lOST 2-3 MPG, WHAT TO CHECK?

[JaMan]

I have been getting much poorer fuel milage, in the last three weeks down from 18. 5 or 17 if I drove it hard, down to 14. 5 to squeezing out 16. What should I check. Newer fuel filter and oil change, cleaned the aFe checked and am going to replace the I. A. T. sensor. There is a few possibilitys but I just don't think they would make much difference. I lifted the front with a 2. 5 leveling kit, but that was about two months ago. Just added 305's to the stock wheels about a week ago since the milage has declined. Where should I start. It has gotten hotter here in Texas, but not much.





Thanks Jared

 

[Steve Campbell]

Things to think about...

Where are you fueling? changes!!!

2 1/2" lift causes more aerodynamic drag..... IMO

Larger tires=speedo adjustments

Air pressure in tires

Really Hot outside air temps!!!

 

[Turbo Horseman]

If you had an exhaust brake I would say check the IAT... maybe do it anyway.

 

[JaMan]

Checked another tank still getting low milage. There seems to be more smoke nowadays but it is getting hot outside. (100+ deg. ) didn't gewt the IAT sensor yet, dealership was closed. I have cleaned it twice in 33,000 miles, can you screw it up using brake cleaner? May be a little low on power but not real noticeable. Could the problem be the larger tires? Has anyone with 305's noticed and dramatic loss in milage. Still no gauges yet, wifes pregnant and won't let me spend and real $. Fixing to do it anyway if I can't figure something out on the MPG. here's current specs.



1. 305/70/16's with 50psi

2. lift pump at 15 idle and 7 at wot

3. Cleaned AFE

4. 3,000 on oil and fuel filter change ( run all highway miles no towing, so aprox 1 month age changed)



5. going to try a I. A. T. sensor tomorrow.

6. 33,000 on truck

7. 17. 5-19. 5 mpg before/ now 13-16 and 16mpg was "grampa"ing it on the highway should have resulted in 19. 5mpg

8 2. 5" leveling kit installed end of June ,and after was still getting good mpg

9. all started about 3-4 weeks ago

10. HELP

11. Help please.

 

[Sticks]

Shot in the dark. . Did you check your intercooler boot clamps?

 

[RowJ]

Steve C. - Doesn't warmer air increase mileage?



Jaman - you didn't answer Steve's question about Speedometer adjustment. You will loose 10-15% mileage going to 305's from stock tires using speedometer to calculate it. You probably knew this (?) but you did not mention it in your reply.

 

[JaMan]

Sorry, I forgot to say that I have checked the hoses recently, but I guess i should check again, and I found one of those tire calculators and am adjusting the milage by 3. 7% that is the difference I under stood from the calculator. example 345miles at a fillup times 3. 7% to get corrected milage. Am I doing this right?

 

[JaMan]

Also on the milage correction I went from 265/75/16 to 305/70/16 aprox 31. 5 to 33"

 

[rraulston]

its the heat and 275 injectors. My mileage went from 19 to 15. 9 after the 275's were installed. The heat is due to the fan running locked all the time. 110 in AZ lately. Ime putting my original injectors back in. after a flow check and cleaning. I have a va and 275's and i can squall the tires and dump tons of smoke. I think smoke=fuel. Lotta smoke=lotta fuel. Wasted fuel. I tow nothing. Ray

 

[jwilliams3]

Check to make sure your fuel tank isnt leaking or your neighbors arent stealing your fuel.

 

[JaMan]

No neighbors, I live where Jesus lost his sandals. Put a IAT sensor in today, will see if it helps, doesn't seem to smoke quite as much, maybe wishful thinking. Does any one know the percentage for refigureing the milage from 265/75/16's to 305/70/16's, I think it is 3. 7% but maybe I'm wrong. Thanks for all the help,





Jared

 

[Steve Campbell]

RowJ....

Really hot air=less dense (less air to burn in the cylinder with same amount of fuel) and Your fan running more often sucking up fuel!

 

[JaMan]

YES

 

[TPlasek]

keep us updated on how that new IAT sensor nworks out for you. I have been wanting to replace mine, but I sure would like to know how yours does first. This way I can learn at your expense



Tim

 

[RowJ]

Steve C.

Doesn't the computer control Fuel/Air mix? If so-will reduce amount of fuel to match available air! Result = Less HP but better mileage in thinner, warm air. Have I been wrong all these years??

 

[lschultz]

I would say them big wide tires is where most of your mpg have gone. I know when Nick had those wide tires on him his he lost some. Now he has the 295 not quite as big but. Somebody had a link where you could adjust things for the size of tire. I think you put in the original size and then the size you are running,gear ratio,and speed you run and hit calculate.

 

[JaMan]

I. A. T. sensor did not seem to help, tomorrow will check all the intercooler hoses for boost leak. Other than a visual inspection how else can I check for a boost leak? Also will check for some axle drag of some sort. Truck is running good just lost milage bad! Waht is the difference in tire size, maybe I'm figuring wrong, but it is still bad. Any other suggestions? Has any body who went up a tire size experienced a 2-3 mpg drop.





Thanks Jared

 

[JaMan]

Just went to dealer , going to have it looked at next Friday. Today tightened all intercooler hoses and changing the fuel filterand oil in morning. Took off the Ez and AFE intake and boost elbow, putting a drop in K&N also to try one more week to figure this out.



In need of Help Jared