Getting bad MPG all of a sudden?

[imq707s]

I've got a 1997 Mercury Mountaineer (just like an X) with 70,000 miles,AWD and a 5.0 V-8. The only mods I've done to it are to swiss-cheese the air box and add a K&N air filter. All through the summer I've been able to get around 275-300 MPG out of a tank full of gas. Now in the last two weeks I've noticed that I can't even get 200 out of a full tank. I don't have a check engine light on, and I've not noticed any decrease in performance. What could be wrong? Could an O2 sensor be going bad? What about cleaning the MAF? Any ideas? Thanks. Also, would an aftermarket exhaust help milage?

 

[EliteConcept]

weird problem... i am not sure what it could be i just know that an exaust won't help you out too much..it does give added proformace and a bit of a power boost..but its slight..i got maybe 1mpg better with my flowmaster on...so its not to big, but it helps.

hope i was of assistance
ryan

 

[aldive]

Have you had a complete diagonstic scan performed? If not, I would suggest one asap.

Keep us posted, we all can learn from other's difficulties.

Good luck....

 

['96explorereddiebauer]

Where do you live?? Since we're well into November, I'm sure some gas stations start selling winterized fuel. If that's the case, live with it. That's the only thing I can say. My V6 Eddie Bauer sometimes can't even make 300 miles a tank in the summer. I remember last winter, the most I get out of in a tank is around 190, 200 miles. But such a dramatic drop is kinda weird. You should get it checked out.

 

[imq707s]

Thanks for the help guys. I'll have to take it somewhere and have it scanned. I'll let you know what I find out. Maybe a bad O2 or MAF? I live in MO so the winterized gas may be a problem also.

 

[kps36]

I would think a 'bad' O2 or MAS would throw a CEL. In absence of the CEL, and at 70k, change plugs (varing opinion on brand), wires, clean the MAS and note any improvement. Also, if not already, change out to syn oil. If you see a CEL in relatively short time, could be a Fuel Pressure Regulator going south. This will, in turn, cause terminal O2 sensor failure.

The exhaust idea is kinda mixed. With the Borla I love to hear the growl, which happens with a heavier foot. It DOES breathe better.

Also, winterized gas is in effect in most areas. Here it is 78deg today in NC and i have dropped 2mpg in last 2 tankfuls.

 

[McFumo]

Hey I'm new here. In fact the explorer I just got is the 1st vechile where I wanted to modify and actually take care of seeing as all my last vechiles were junk.

Anyways, anyone from the wisconsin area know if they winterize the gas? I'm getting about 16.5 now mixed which isn't all that bad, but I just want to know if I'll be filling up more in a couple weeks.

 

[aldive]

Originally posted by kps36
I would think a 'bad' O2 or MAS would throw a CEL. In absence of the CEL,

Not always, I recently went through the nightmare from hell and it turned out to be an O2 Sensor. See the thread called "Alarm system woos".

Good luck....

 

[DesertSpive]

Bad O2s do not throw codes on the most Rangers and Exs, because it doesn't know its bad. It will go bad, and stay in open loop (basically thinks it is on start up) and run incredibly rich. Thats where all your gas goes, plus the winterized gas doesn't help. Very common on these vehicles. Plus if it hasn't been replaced I see most of them go bad on 4.0L around 60-70,000 miles, so you are definately in the ballpark for your 5.0L.

--Sean