Hey guys,
looking for some advice/thoughts:
2010 F150 4x4 5.4 super cab. Truck has 202,000 miles / Engine was replaced with a Jasper Remanufactured at 131,000. Gas mileage has recently dropped by 20-30+%. There is a hill near me that I've use as a sort of controlled test with a specific start/end point & specific speed for quite a few years- normally would get 9.4-9.8mpgs now I'm lucky to get 7.0 usually is in the mid 6s. Used to often see 20 mpg on some freeway trips- Now looking at 14-16 mostly.

I drive alot and I usually drive for mileage- got 192,00 miles out of the first set of brakes- and so I am very familiar with the trucks habits.

I took a trip to my sisters(635 miles away) I started out hoping to make it on just one tank- took me almost a tank and a half.

Looking at replacing O2 sensors but doesn't sound like much fun after reading about it- not too interested in throwing money away replacing functioning parts. Is there a life expectancy on o2 sensors- should I just go ahead and do it?

maintenance done recently:
201,000- broke down in Doris CA. Dealer replaced crossover tube and thermostat. Also replaced water pump although it may not have been bad- but with with the miles on it and it being at the dealer it made sense.

170,000
new plugs and cops

190000-192,000.
Brakes- new rotors and pads
Shocks/Struts- Rancho 9000 with no change to ride height
New tires (3rd set of michelins- yes I've checked the air pressure, numerous times)
Transmission flush
Air filter

**PCM reflash- This might be important. Truck didn't pass it's first smog check due to PCM communication issues. Smog center's tool would not read the PCM. What may have happened is that I was running a 5Star tune on the vehicle and forgot about that when I had taken it to be smogged. When the technician described the problem the lightbulb went off and I said "let me check into this and I'll get back to you". Went home and tried to return to stock but 6 year old SCT programming tool had failed. SCT techs tried to help but in reformatting the programmer they wiped the original stock info and the solution to that made matters worse- every dash light lit up and stayed on. Dealer reflashed for $350 and said the PCM was no good- probably fried by the sct programmer or program fried it- Was quoted $1500 to replace it. I asked if the vehicle was driveable which said yes and then stammered out several reasons (check engine light was on and it wouldnt pass smog) so he preferred to keep the truck until he got the $1000 PCM in... I didnt feel the dealer was completely honest with me several times in this exchange and so dont really believe he knows the program or programmer had anything to do with it as previously there was never a problem switching the stock and custom tunes which I did every time it went in for service. Ill probably add a tune back once this is straightened out(probably not using and SCT tuner though). Once I got the truck home and read the check engine light the code said something about final gear ratio not found (3.73 LS). Cleared the code and then took it to the smog center where it passed with no problems.

Currently the only visual cue something is amiss is that my traction control light is on but whose to say whats really going on in its pretty little head...

I have noticed a couple of other changes since the PCM reflash specific to the PCM. My speedo is now accurate or a mile slow. Previously it was 2-3 miles fast. That difference doesn't equate to the drop in fuel efficiency though. The other change I notice is that the oil change and low mileage warning messages now flash when mileage is low or oil change is needed(whereas before they were just solid until you cleared them).

Truck runs smoothly just is getting terrible gas mileage.

Thanks for your time.
Tim

 

Oxygen Sensor Life Expectancy
http://www.popularmechanics.com/cars...a1985/4219927/

Note.. only the forward sensors affect engine operation the rear sensors only monitor cat function so don't bother changing these unless there is a specific code for them.

 

That is a lot of miles on an O2 sensor, but it doesn't mean you need to run out and replace it unless you are wanting to be proactive. The oxygenated fuels used in the winter time have less energy per gallon. That could be why your mileage is down.

 

The PCM will test the response time of the upstream HO2S once per drive cycle. This is about a six second test performed by adjusting the fuel mixture rich and lean and measuring the response time of the sensor voltage. If the sensor fails to respond within spec the PCM will set the P0133/153 DTC depending on the bank 1 or 2.

 

Thanks for the links. Ill shoot for just replacing the top sensors. Looks like the replacement process in the video (on the nissan) was pretty simple. Most of the previous instructions I found involved words like PITA, busted knuckles, blood, etc.. I'll see if I can pick up sensors today and then try it tommorow.

EDIT: Was distracted by things this AM while replying to the first response and didnt see two new responses before posting.
Re:
the winter blend- yes absolutely right about reduced mpgs + really cold weather for our area this winter but still doesn't account for all the drop in mileage. Recent 200 mile downhill run from Tahoe netted 17.9. Whereas previous similar runs in similar weather will normally produce 20 mpg+ (cruise control just under 65)

PCM is the real wild card here as there is some sort of error involved with it. The lit dash light for the traction control is my indication PCM is not 100%. Does that impact mpgs? Unknown. What I really want is to have it reflashed again but dealer is not helpful and would charge me $350 each to do that. My connection at ford can get me a PCM for $600 plus programming brings it up close to $1000. I can buy a discount programming tool for a 800-$1000 and ford will sell the program for $32 and you can buy a used PCM off Ebay for $150 +/-. Of course the ebay route may have its own issues with obtaining a truly functional PCM that is actually appropriate for my vehicle. My part counter buddy was a little surprised when he found something like 8-10 diifferent PCM # used on the trucks. Of course only one is specific to my truck.

So there are a couple of paths I can travel here and it seems like the O2 sensor might be the cheapest way to start. Plan on keeping the truck another 100,000 miles so changing out the o2 sensor now will still give me a few years of use out of the replacement.

 

Yes, If you're keeping the truck long term I would suggest replacing the O2 sensors even if it is just to keep a problem from occurring. Their output tends to drift a bit after time.