Bad gas mileage

[lilazndemon20]

I just moved from Las Vegas to the San Francisco Bay Area and my gas mileage just went to crap! I'm talking about 13 mpg. My tires are inflated properly, air filter isn't extremely dirty, and my driving habit's have not changed. Granted I'm taking more short trips on more local roads but I don't believe that it would cause the mileage to go down THAT much! What could be the problem?

[Warhammer]

My knee-jerk-reaction is dirty injectors, your knock sensor is bad, or you have a vacuum leak somewhere on the motor.

Lots of people in this forum says that if you always fill with "top tier gas" you're injectors will never clog. I say:

I'm an acetone fan and have used the stuff for a VERY long time. Go to the gas station, put 6.5 fluid ounces in your fill port with a funnel, and then top off your tank. Don't get the acetone on your paint and use a glass beaker or pyrex measuring cup. The acetone will completely clean your entire fuel system, injectors, and lines. Your performance and MPG should drastically improve. You may have to do this for 2 tanks to get the full cleaning effect.

If it's your knock sensor, you should have your codes read at the local AutoZone. I don't believe a bad knock sensor will cause the engine light to turn on. I had a 2002 Nissan Frontier V6 that had a knock sensor go and I noticed very poor performance and a drastic reduction in MPG. Still drove okay, but that spunk I really enjoyed wasn't there.

If it's a vacuum leak then air is getting into the engine. But you would feel your engine idle kind of rough sometimes or feel the power surge in and out. Your description leads me to believe that it's not this. But...not much detail was given.

Hopefully this helps. Do these things and report back with good news!

[njjoe]

l20-

The MO's fuel efficiency is heavily influenced by the terrain and driver's habit.

Although I can get close to 30 MPG when doing 55 MPH on a flat highway, my fuel efficiency drops to the high teens when in city driving mode. Throw in some hills and spirited driving and I am now seeing low to mid teens.

-njjoe

[lilazndemon20]

thnx for the responses. I didn't notice a rough idle and any drastic performance changes. I will try cleaning out my injectors although i believe i ran some sea foam through it not too long ago.

[shelland]

When watching the mileage screen (which obviously isn't exact), I'm always amazed at how much difference a very small incline will make. Are you driving a lot more hills than you used to (given it's San Francisco), or are you mostly in a fairly flat area?

[lilazndemon20]

im not in san francisco. i'm in fremont which is about 40 minutes away. It has some hills, but not nearly as extreme as SF. I bought some acetone and put it in the tank today. I went to autozone and they didn't have a scanner but said it was possibly the o2 sensors.

[Eric L.]

13-15mpg would be what I would expect if I drove a lot of short trips of less than 5 miles. I get 15-16mpg driving around town, but then I have a short commute of only 5 miles. No hills.

When the vehicle was newer and I drove a further distance in the city in heavier traffic, I got ~17mpg city.

[lilazndemon20]

i noticed that when i would start the car sometimes it would almost die right after it starts. The rpms would drop really low and the engine would struggle and then go back up to normal. Don't know if i put too much acetone in or what?

[Eric L.]

Personally I wouldn't use acetone in my gas tank, as it is against the advice of every mechanic I've asked. If such a small amount makes a difference, don't you think Exxon Mobil or Shell would just add it to their gas, get 15% better fuel economy, and charge more money for it?

But to each their own.

[njjoe]

Originally posted by lilazndemon20
i noticed that when i would start the car sometimes it would almost die right after it starts. The rpms would drop really low and the engine would struggle and then go back up to normal. Don't know if i put too much acetone in or what?

How much did you put in? You can always dilute it further by topping off the tank.

Next time I suggest you stick to products that are purposedly designed for the task.

-njjoe

[Warhammer]

I seriously doubt the acetone is what's causing the RPM drop on startup. I ran the stuff through a few tanks after I got my MO and no adverse affects at all. If anything, my MO averaged 22.8MPG withthe acetone versus 21.5MPG without it.

It sounds to me like you have an issue with your idle air volume. Las Vegas is about 2000 feet above sea level and San Fransisco/Fremont area is almost right at sea level.

Have you had your battery disconnected recently?

When I first got my MO I had CarMax fix the audio switches on the steering wheel. They disconnected the battery the entire time they were performing the rework. After I got my MO back, the motor would do exactly what you're describing. Upon startup after the motor is warmed up, it would go down to a very low RPM and sometimes compltely die out.

There have been others in this forum that have had to relearn their idle air volume just out of the blue. No battery disconnects from what I could tell.

[lilazndemon20]

I did disconnect my battery a few days ago. So this problem will go away with time?

[Warhammer]

Boy I hate being right sometimes.

As far as I can tell...no. You will have to do a Idle Air Volume Relearn if you don't want your MO to stall out or hesitate on start-up. You might as well do a few other relearns as well.

Part 1 of 4:

[Warhammer]

Part 2 of 4:

Idle Air Volume Learning

Setup conditions parapharased:
1) Drive your car around for about 10 minutes and park it.
2) Turn everything off (radio, headlights, blowers, ac, heater, defoggers, wipers, etc.).
3) Center up your steering wheel and make sure your wheels are facing forward.
4) Ensure your praking brake is not on.

[Warhammer]

Part 3 of 4: