MPG is going south. Not Good.

[FreshAir]

I have, I think, recently noticed a decline in MPG from apx. 7 to 7 1/2 mpg to about 5.5 to 6 mpg. I have an 05 WH with the 8.1 with 24,000 miles. I drive between 62 to 65 mph . The last few trips of about 300 miles or so, not bad terrain, seem to get me about 6 mpg at best. Measured with pencil and paper at the pump. Same tow weight. IP avg. MPG seems to validate the pump MPG.

I haven't replaced anything, stock air filter, have spare Omey's fuel filter somewhere, never replaced, just stock. Seem's to run fine, no miss I can tell. Same plug wires, haven't checked them.

Just wondering if you guys were me, what would you be checking for at first glance? All suggestions are welcomed.

Thank's, Pat

[ron55]

ethanol did that to me

[speed racer]

I would check the air filter and make sure it's going into overdrive.

[DriVer]

Quote:

Originally Posted by FreshAir Just wondering if you guys were me, what would you be checking for at first glance? All suggestions are welcomed.

FreshAir, In my experience, bad O2 sensors were causing me great pains with my MPG ratings. Once replaced the MPGs went back to their norm. You will need to have the O2 sensors scanned, a Tech II helped me identify the bad O2 sensor. I changed both no need to have one better than the other.

Of course you have to rule out the air filter first. I do get better results from non-ethanol gasoline BTW.

[powderman]

I would check the o2 sensors assuming they have them in the GM 81. series. A bad o2 sensor causes lower fuel mileage by making the system run rich. In autos at least, they will not always throw a code right away, but will show up when scanned with the proper equipment.

[RottenRalph]

I'll also blame ethanol. I also have lower mileage using Shell gas.
And, just prior to my fuel pump going out, I was getting about 5MPG.

[FreshAir]

I never thought about the ethanol thing but I am aware of what it can cause. Filters will be replaced. I wish I hadn't heard about the fuel pump turning to toast.

About the 02 sensors? What's involved in replacing them? Can I do it under the "Shade Tree?" I have the "Scan Gauge" from Linear Logic which shows no codes existing. Would it show a code for this if I had one?
Thank's
Pat

[RottenRalph]

Quote:

Originally Posted by FreshAir I never thought about the ethanol thing but I am aware of what it can cause. Filters will be replaced. I wish I hadn't heard about the fuel pump turning to toast. About the 02 sensors? What's involved in replacing them? Can I do it under the "Shade Tree?" I have the "Scan Gauge" from Linear Logic which shows no codes existing. Would it show a code for this if I had one? Thank's Pat

To clarify: My mileage started dropping off about one hour prior to engine missing then stopping. Allowed to cool then made it home.

If your still running ok, it's probably not the fuel pump.

[cds281]

The gas milage fell off in my 8.1. Replace spark plugs wire & it help. I also thought that I had an exhaust leak. The mechanic replace coil pack on number one cyclinder & fix my problem. Run good & gas milage back up & no exhaust leak. 2003 8.1

[DriVer]

Quote:

Originally Posted by FreshAir About the 02 sensors? What's involved in replacing them? Can I do it under the "Shade Tree?" I have the "Scan Gauge" from Linear Logic which shows no codes existing. Would it show a code for this if I had one?

Pat, There isn't an instrument that completely cover all the bases as much as a Tech II will. Shade tree O2 sensors, possible. In my experience, there was a much younger guy than I changing my O2 sensors and he came out exhausted! Stand-by to pull hard!

[FreshAir]

Quote:

Originally Posted by DriVer Pat, There isn't an instrument that completely cover all the bases as much as a Tech II will. Shade tree O2 sensors, possible. In my experience, there was a much younger guy than I changing my O2 sensors and he came out exhausted! Stand-by to pull hard!

DriVer, Why would the O2 sensors on a WH chassis be so difficult to R&R. Is there one in a really tight spot? I guess I need to crawl under and take a peak. At 24K miles and no rust they hopefully won't be froze. Wish I had access to a Tech II as my Scan Gauge won't read a lot of codes but was hoping someone might know. I know a lazy sensor will impact MPG but it may not even be posting codes yet if I do have a bad one, I don't know.
Thank's to All for your input.
Pat

[DriVer]

Quote:

Originally Posted by FreshAir DriVer, Why would the O2 sensors on a WH chassis be so difficult to R&R. Is there one in a really tight spot? I guess I need to crawl under and take a peak. At 24K miles and no rust they hopefully won't be froze.

Pat, No tight spots, they are right out in the open. Your experience may vary. That said the O2 sensors are located in just about the hottest part of the exhaust pipe and it would be very unusual to see rust there. The sensors that the tech was yanking on on my rig - - - were challenging to say the least.

[Mr JP]

The mileage on my w-24 chassie has been best at 7. I ran a Tech II scan and it showed both o2 sensors with a low voltage code & NO check engine light !! I have now changed both o2 sensors and installed the Ultrapower and a set of Taylor wire extremes. I will go on a trip in about 2 weeks so that will be the test. My test drive was very impressive with the UPS . I always write down my mileage and fuel so I will be able to track the change. Good Luck

[DriVer]

Quote:

Originally Posted by Mr JP My test drive was very impressive with the UPS .

Are you driving the BIG Brown Truck ??? It's a Workhorse you know.