Other than 7500lbs and 10 cylinders! LOL

I`ve been trying for a while now to figure out where my fuel mileage went to. to bring you up to speed........ over the course of the last 3 years my mileage went from 12.5 city/hwy to 10 and my towing mileage went from 8.3 down to 5.5-6mpg! I attributed this to the Ethanol they have been adding to the IL gas.
I bought my X at 2 1/2 year old and 17k miles. on one trip 2 years ago I filled up in WI with 40 gallons of 93 octane pure gas (no ethanol) WI. gas and it felt like I had 50 more HP! and my mileage came back up. that slowly also went away and even running that now results in no improvemnts.
I`ve done everything you could do to improve mileage, at 50k, T-up, clean MAF, replace PCV, clean T-body and replace fuel filter. nothing helped. so I`ve been dealing with it.
well today I plugged in a different scanner than what I was previously using and guess what I found? found the Bank 2 O2 sensor stuck at 0 volts and the Short Term fuel trim stuck at 99.2%. Bank 1 is switching like it is supposed to. I think maybe the O2 sensor was intermittently going in and out. I have no codes, the reason is because the 8900lb GVWR X runs an OBD I fuel system which just monitors and doesn`t run some diagnostics or report issues. Looks like mon. I will be replacing both O2 sensors. and I will report back with any changes.

Just thought I`de share a little something in case someone else has similar issues. If anyone has any questions please ask, I may have left out some info.

 

Very interesting, it shocks me that the fuel trim could be that far out of whack without setting a code.

I wonder what damage may have been done by running rich for that long.

 

Running rich is much better for the engine but worse on the wallet. It will foul plugs and wreck the cat. Running lean will cause overheating and burn holes in the pistons.

 

I know my chrome exh. Tip has turned blue! When I pulled the plugs at 50k they looked normal. I'll take a pic of the scanner with the readings. I agree it is odd that it is not setting a code. It is an OBD I system and I know they are very lenient on setting a code which is why they came out with OBD II which will throw a code if you sneeze wrong!

 

You may have found something, but it may not be what you believe it to be.

Let us know what the readings with the new sensors installed.

 

I only get that mileage also. My trims are right in line and my O2 sensor is switching. I do get around 8 mpg when towing though. I figured mine is rings and age. Which is why the new motor. Plus PI heads and ABS lower plenum. Really hope this helps. Very curious to hear the results.

 

OK, after getting some sleep and thinking about it, I rechecked what I was looking at. that 99.2% and 0 V reading was for the downstream O2 sensor, which obviously I don`t have because it is OBDI. I wasn`t reading it right, I guess being tired and having a couple beers does not make you think straight! LOL My scanner does not read BNK 2 O2 for some reason. so now I will go back and recheck with the other scanner and see if it reads BNK 1 and 2 sensors. I do know that under load the X will surge occasionally. and the bank 1 and 2 fuel trims were equal, so I believe the O2`s are operating correctly. I did notice when I was looking under the X this morning that there is a slight leak at the exh. manifold flange (manifold to head pipe) not noisy, but you can see where black soot is tracking out of the flange. I wonder if the CAT is possibly partially plugged? more things to look at! The more I thought about it the truck would be running like crap with that reading!

 

Some of your problem may be fuel related and it may not be just the 10% ethanol. We travel all over the country with our 2V V10 and anymore our mileage is all over the place. Some of the blenders of fuel are removing things out of the fuel when they add the 10% so they still end up with 87 octane and I think that at times you end up with more than 10% because the ethanol is a little cheaper. I know from first hand experience that the further east you go the the lower MPG we get out of our V10 and it doesn't run as good as it does in the Midwest, the worst we have found is Florida with the rest of the state on the eastern sea board not far behind. A couple of weeks ago we filled our aux tank with non ethanol fuel I think in Oklahoma and didn't transfer it into the front tank until it was almost empty so there was very little 10% left in the tank and I could not tell any difference in my mileage or pulling power but I did get just a little ping that I always have with straight gas. The 10% that I was burning was from Nebraska where they take straight gas and add the 10% and change nothing else, they end up with 89 octane.

Other things to think about, have you gone to a more aggressive or larger tire, have you checked your slide pins on your calipers lately to make sure they are moving freely so the brakes aren't dragging (it doesn't take much), and last how may more miles do you have on the motor, I know that our mileage has dropped of overall over the years and I think some of it is from engine wear over the last 12 years and 123K hard pulling miles, nothing last forever.

Denny

 

My last 2000 F350 V10 was 7-8 towing 7000 pounds and 10-13 going up and down the mountain. After 25000 I know noone getting anything different that actually uses a calculator to figure out MPG. My friends overhead tells him 17MPG but he knows better. I love my diesel now but I was impressed running 5000 RPM and pulling that heavy trailer over the hills of the Colorado pass I-70. Now I get 17-20 MPG on the mtn and am saving up for another road trip with the trailer. Diesel Ex is awesome.

 

Are you SURE it's OBD I? My 2000 is OBDII.

 

It is OBDI anything over 8650lbs? GVWR runs the OBDI sytem. the X`s with the 5.4L have the OBDII sytem. my X is rated at 8900lb GVWR. I still haven`t had a chance to look into anything yet.

 

I could be wrong but anything after 1996 until 2008 is OBD II.

 

I think you will find that anything with EGR is OBDII and without is OBDI at least on the 2V V10. My 2000 V10 with EGR and California emissions is OBDII.

Denny

 

It depends. There is a sticker under hood that says obd1 or 2

 

Are connectors under the dash the same?