Gas Mileage Drop

[kingwilly]

2004, 120k miles, finally did a tune up. Changed plugs, gas filter, air filter, oil change, PCV valve....(1st time for plugs and PCV) I swear my gas mileage dropped. I believe I use to get 17 mpg on highway, now it is consistently 13 mpg.... I took my time on the plugs (no choice...lol), lubed up the boots and everything went pretty smooth. Any clues? Take to a tune up shop and have them hook it up to some diagnostic equipment? Punt?

KW

 

[JUST4FUN]

is the motor getting to operating temp?

 

[kingwilly]

yes on operating temp....I do a lot of one hour plus trips and have done a few since I put the plugs in. If that what you are asking. I feels like it pulls pretty strong. Wouldn't it stumble if a wire was off or a coil was bad?

KW

 

[JUST4FUN]

if the thermostat is bad or the wrong one the computer will try to get to operatinf temp by useing more gas. this will show a code
also if the mass air is dirty, a vacuume leak wil;l caause this

 

[kingwilly]

I took it into a fairly reputable repair shop yesterday. They checked the codes and test drove it. They found nothing wrong and didn't charge me. I will look for a vac leak. Getting 13 mpg on the highway sucks....

KW

 

[joezek]

also try resetting the computer by unplugging the battery for a while. Maybe better airflow and fuel pressure is screwing with your computer?

I was getting about 17 mpg at 70 and 20 mpg at 60. I made an injector rail fuel injector cleaner. I did the injector pressure clean and changed my fuel filter. Now I get 22-23 mpg at 60, and 18-18.5 mpg at 70. Just drove 5 hours yesterday on the highway and verified the mpg driving to Orlando.

If it's running smooth, no codes, and no power loss I really don't see how the mpg would drop that much. Is your airfilter a paper type? Maybe dirt or oil is now on your MAF sensor. That will screw up mpg real fast.

 

[kingwilly]

I think I will try some fuel injector cleaner in the gas tank, see if that helps. I will disconnect the battery now and see if it resets anything. Any suggestions on how to clean the MAF sensor?

KW

 

[Shadow-D]

Something no one has mentioned...

One thing to look at is your fuel. Do you get your fuel at the same place or several places / cheapest?

Reason I'm going in this direction is Ethanol. Most places are allowed to add up to 10% and I think they recently passed something that allows stations to use up to 21%. It could be something as simple as too much ethanol in your fuel.
Solution, find a place that sells ethanol free fuel and your mileage will go up. It won't be too noticeable in the first tank but you should start to see an improvement after the second tank. After 3 tanks you will want to disconnect your battery overnight so that the computer "relearns" itself.

 

[kingwilly]

I usually go with BP 87.....I really don't go to the cheapest gas station. I will disconnect the battery tonight and see what happens. Why all night?

KW

 

[Shadow-D]

I usually go with BP 87.....I really don't go to the cheapest gas station. I will disconnect the battery tonight and see what happens. Why all night?

KW

If you have been running gas with ethanol and switch to 100% ethanol free fuel thats when you need to unhook the battery.

Some people say to disconnect the battery for 1/2 hour, some say an hour, some say 3 hours and some say over night. I say over night that way you know the mem is cleared.