7mpg drop in 1week......any clues???

i know the general "how to improve your gas mileage" drill, since i try to sell it to people daily at work.

but this one has me a little stumped.

i have a 95XJ 4.0L, AW4, 3.55 w/31" tires.

beginning of the year i hydrolocked my engine, so i got a new one out of a 94grand cherokee and cleaned it up and re-sealed it. after the engine swap i was getting about 20mpg on the highway and 14-15 in the city.

now for the last few weekends i've been driving to a friends farm 2.5hours away to go wheeling with him. every time i would go there i used just under 1/4 of a tank each way with the cruise control set at 60-65mph.

but these last 2 weekends i used almost 1/2 tank each way with the cruise set at 60-65mph. so i ran my mileage, and it seems that my jeep dropped from 20mpg (on the highway) to 13mpg (on the highway).


i do a tuneup to my jeep EVERY year (plugs, wire, cap, rotor, belt, etc......mostly because i ride my jeep very hard, and like to know the condition of things).

but what would cause my mileage to drop 7mpg in 1week, and then stay so consistent??? i fill at the same gas station every time. the jeep runs great, sounds normal, and no check engine light or other weird indications.

Hanging e-brake maybe?
If it is on just a little, you might not notice it.....

Or of you've been wheeling...Air cleaner plugged up some maybe?



Jim

When's the last time you replaced your o2 sensor?

Usually the first sign its going is a drastic drop in mileage...

-C

scorpio_vette said:

but what would cause my mileage to drop 7mpg in 1week, and then stay so consistent??? i fill at the same gas station every time. the jeep runs great, sounds normal, and no check engine light or other weird indications.

Click to expand...

The timing of this is too perfect.

Firstly... the temps have been dropping... especially up your way... which might have an effect... but...

Secondly... here in PA, we we switch to a different blend of gas (mandatory) on Sept 15th... a "winter" blend with the wonderful "oxygenates" in it (used to be MTFE, no idea what's in it now). I wonder if you guys do, too? (There are stickers on our pumps about "Cleaner Gas April 15 - Sep 15" or some such nonsense.)

I've had cars that would instantly show a drop in MPG very similar to yours when running on oxygenated gas.

Den

I believe they are using ethanol in place of the MTBE now.....

Jim

What about the cat maybe its pluged up or something? And what about RPM's at hwy speed maybe your TQ converter isn't locking anymore?

Winter formula gas?

I am betting on an O2 sensor going south. They often fail before the check engine light comes on. My fiance's failed last month and her mileage in the altima went from 29 to 23 overnight.

my gas mileage also dropped seriously over the summer and it was my 02 censor and it also happened to my buddies toyota tacoma and it was somethin with his throttle body. good luck bud

i had to go for emissions about 5 months back and replaced the cat, O2 sensor and the entire cat back at that time. reason for replacing it was that my cat had previously collapsed, and so i temporarily hollowed it out. and i didn't know the history on the O2, so i replaced it along with the cat and tuneup, that way i know it had a new one in it.

i was thinking about the winter formula crap, but would it really knock it down that bad??? i could see 1-2 mpg, but 7???

Did you replace the upstream o2? When mine went it gave me bad mileage, power loss, and bad idle until it was warm. Never threw a CEL.

95XJ........only has 1 O2 sensor

Check for leaking fuel at fuel rail, injectors, fuel filter and everywhere in between.

I get 11-12 in the city all the time.......30's, cracked exhaust header.....llol.

DenLip said:

The timing of this is too perfect.

Firstly... the temps have been dropping... especially up your way... which might have an effect... but...

Secondly... here in PA, we we switch to a different blend of gas (mandatory) on Sept 15th... a "winter" blend with the wonderful "oxygenates" in it (used to be MTFE, no idea what's in it now). I wonder if you guys do, too? (There are stickers on our pumps about "Cleaner Gas April 15 - Sep 15" or some such nonsense.)

I've had cars that would instantly show a drop in MPG very similar to yours when running on oxygenated gas.

Den

Click to expand...

I was wondering about that. I remember hearing that a while back, but hadn't thought about it in a while. Aren't different counties up here on different formulations as well? I seem to remember somebody saying something about Allegheny and Westmoreland (Pittsburgh area vs. rural area for anybody wondering) getting different gas.

In colder temps gasoline is most dense......yadda yadda yadda.

Cold temps shouldn't decrease your MPG that much, unless you are remote starting your vehicle for hours and hours.

everything on the engine is new (just replaced it beginning of the year after hydrolocking my old one), but just incase i double checked all the fuel seals, and didn't see any leaks.


oh yeah.......i used my remote start 1X for 5minutes.

but like i said, this is a 2hour highway trip that i noticed this on. nothing on the route has changed.....cruise control at 60-65mph every time, and same gas station every fill up. i can't seem to figure this one out.

Those OBDI-O2 sensors are cheap, change it out.

BTW I read that we all use the same gas in the winter except maybe cali, in the summer there are approximately 60 different blends for the 60 largest metro areas. Part of gasolines high prices are transporting the 180(3 octane levels) different fuels thoughout the country.