Sudden drop in MPG, any suggestions...

[TCordero]

My 04. 5 has just over 9,000 miles on it and I have been getting 17-18 mpg all along. My last tank the mileage had dropped to 14. 1 and all indications on the current tank are the same or less. I'm at 1/2 tank in 160 miles. The only difference in my driving is roughly 30-40 miles in 4wd on the last tank. The driving in 4wd was done on the hiway 35-40 mph. I can't imagine that 30-40 miles would make that kind of impact on a tank of fuel. Not to mention this tanks seems the same. Is there a way to check to see if the auto hubs have unlocked? Would the hubs staying locked have that kind of impact? Anyone with similar scenarios? Going in for service next week, the dealer said they would hook it up to the computer and "check it out". I'll keep ya posted-



04. 5, QC, LB, 6sp, 4x4, 3. 73's

 

[JL penner]

Check your air filter. Used to have an 03, and had the same thing hapen, only I was at 7000 miles. Just messing around I pulled the air filter and it was completely clogged!! Worst part was it was on a weekend and at that time you could only get filter from dealer!

 

[roperteacher]

I reported this on this same board here a few weeks ago. Mine will do this occasionally for some odd ball reason!! It happened once when it was brand new, then a 2nd time here a couple weeks ago. I could SWEAR someone was stealing fuel from me etc. I changed the air filter and fuel filters. I usually get close to 20 MPG around town and 22 Hwy empty. I can see 16-17 Pulling If I really baby it. . One tank I just got like 14 and reported it on here. I got responses about fuel filters, Air filters, #1 diesel ( Which I live in sunny so Cal so that was not an option)... . THen I fill up and the very next tank is back to 20 MPG!!! I haven't taken it in because it has no codes and runs really good etc... let me know what they say!

 

[nickleinonen]

#1 diesel ( Which I live in sunny so Cal so that was not an option)

more so an option than you might think... when burning #1 fuel, NOx emissions are much less than when burning #2 fuel. here in toronto, the TTC transit bus' all burn #1 to produce less NOx which means less smog... they might be selling more #1 in cali, or blended #1/#2 to reduse emissions...

 

[TCordero]

Thanks for the input, I'll check the air filter. Also, where can I get #1 diesel? As a side note, these 2 tanks of fuel are both from the new Safeway that just opened with the best price on fuel?? and the service is a scheduled oil change, the inquiry on the mpg issue is a side note.

Thanks again...

 

[DJennings]

Try filling it up where you used to get fuel. Your new Safeway may not be selling the best diesel (lower cetane), and that will cause the reduction in mileage. If your mileage goes back to normal, then you found your problem.



Cetane boosters will also have a more dramatic effect when the cetane of the diesel you buy is lower. If you have a full tank right now, try a cetane booster (additive) like Stanadyne PF. I talked to a guy at a local diesel shop today about the cetane boosters and how they affect mileage. This is what I got from him. Not everyone is OK with additives in their 3rd gen CTD's, so that is up to you.



I would still check all the other things in this post, but if nothing is showing up, this could be the simple answer.