Gas mileage fell off a cliff!

[Rocket]

The last four tanks have been terrible for gas mileage! I used to get 23 - 25 mpg, now I am getting around 20 mpg!

The only change I made was a new air filter. I'd expect mileage to improve. But it hasn't. Tire pressures are correct.

Any ideas? I'm thinking I'll check the air filter, but that seems unlikely.

Thanks!

 

[mazdaspeedster3]

Go to the auto parts store and get MAF Cleaner... Sometimes changing the air filter will throw your MAF off. It is easy to clean. Pull it, unplug it completely and then spray every bit of it with the cleaner, directions will tell you 15-20 good blasts. Then reverse install. That should help you out!

 

[Robotazky]

Go to the auto parts store and get MAF Cleaner... Sometimes changing the air filter will throw your MAF off. It is easy to clean. Pull it, unplug it completely and then spray every bit of it with the cleaner, directions will tell you 15-20 good blasts. Then reverse install. That should help you out!

That, and try just resetting the ECU by disconnecting the battery (-) terminal overnight.

 

[Rocket]

Where is the mass airflow sensor? I'll clean it and reset the ECU.

 

[Robotazky]

Where is the mass airflow sensor? I'll clean it and reset the ECU.

It's on your air intake. Look between the air filter and the throttle body for a part with a plug that goes to the computer. Carefully take the plug off, and I'm assuming it will have a couple of screws that you remove and the MAF will come right out. Go buy MAF cleaner. It's a spray can of liquid that is safe for electronics.

 

[Rocket]

I went out and cleaned it. Though it is dark now, it was visibly dirty. Battery is disconnected, I'll hook it back up tomorrow. Thanks amigos!

 

[Robotazky]

I went out and cleaned it. Though it is dark now, it was visibly dirty. Battery is disconnected, I'll hook it back up tomorrow. Thanks amigos!

Let us know what happens.

 

[coolmazda5]

Maybe coincidence, but Have you tried a different gas station just in case? I've experienced that before...

 

[Rocket]

Yes, I've shopped around. I rarely use the same station. That was my first thought also, but four tanks later it is just getting worse.

I'll know today or later this week if there has been an improvement.

 

[Rocket]

Too early to tell if the mileage has improved, but the car stalls when coming to a stop. It has happened about 10 times so far this morning.

 

[Robotazky]

Too early to tell if the mileage has improved, but the car stalls when coming to a stop. It has happened about 10 times so far this morning.

You did use MAF cleaner, right? Did you blow the MAF out with air and do everything you could to dry it? I would check it again tonight to see if it's dry. I noticed last time that I used MAF cleaner that it didn't evaporate quickly like throttle body or brake cleaner. Maybe it's still wet or something.

 

[Rocket]

I used MAF cleaner. It sat overnight, I'm sure it was dry.

Anyway, no stalls this afternoon. I filled the tank, I'll know in a day or so if the mileage has improved since I drive about 100 miles per day (car has 93,000 miles!).

Thanks for the tips!

 

[diogenes]

I sometimes get poor mileage this time of year when the stations switch to "winter gas" with more alcohol in the mix, which is required to address air quality issues. Alcohol has less energy per volume than gasoline, so mileage suffers. That's good advice above about cleaning the MAF sensor, though, especially since you've already addressed the most likely problem by changing the air filter

 

[Rocket]

As a follow up, the mileage is still not where I'd like it to be. Today was 21.2, compared to an average in the 23.5 range. I'm going to take another look at the air filter and replace it with another brand. While it is hard to imagine that a new filter would cause the problem, I am going to undo the last thing I did and see what happens.

Stay tuned...

 

[harrye357]

The last four tanks have been terrible for gas mileage! I used to get 23 - 25 mpg, now I am getting around 20 mpg!

The only change I made was a new air filter. I'd expect mileage to improve. But it hasn't. Tire pressures are correct.

Any ideas? I'm thinking I'll check the air filter, but that seems unlikely.

Thanks!

Hello,
Had a similar problem on my 95 Protege. Turns out that the ebrake cable was stuck and the right rear brake was dragging.
Harry

 

[justanothermp5]

change ur oil?

 

[SGT_OKINAWA]

Whoa. (smash)

Can I just say something, just .02 worth?

There could be one of 100's of things wrong, lets see what I can post off top of my head:

1. Cargo, you are carrying too much junk in the truck.
2. Tire Pressure
3. Tire wear, poor tires effect performance.
4. Charging system going, if it has to work harder that can drop performance.
5. Air filter is dirty.
6. Oil Change to a grade / weight for the season and temperatures.
7. Air Flow sensor is all jacked up, broken regardless if it is dirty.
(hah)
*The advice so far is like saying, "Hey have you washed your tires so you get better traction?
8. CPU has a timing glitch and when acceleration is applied the engine is not functioning as it should to down shift, shift accordingly, etc.
9. Parking brake is stuck (Someone said that)
10. If the bearings that allow the crankshaft to turn freely are worn out, the crankshaft cannot turn or cause the engine to work harder.
11. The oil you used is bad, or wrong kind like the 17 year old kid at quick lube used the wrong kind.
12. The Octane of the gas you are buying is off.
13. Lack of spark - The spark might be nonexistent or weak for a number of reasons.
14. Coolant is low and causing the engine to run hotter.
15. Fuel filter is dirty
16. Belts are slipping causing problems
17. Lack of compression, "hole" in a cylinder occurs where the top of the cylinder (holding the valves and spark plug and also known as the cylinder head) attaches to the cylinder itself.
I could go on and on, advice
Get a code reader and read the car codes,
18. See if the rear pig (Differential) (I know not on a 5) oil needs changed or is low.

Anyhow, before you spend 100s a of $$ trying all the shade tree mechanic remedies, I check the codes and or take it to a TUNE SHOP and get it over with.
Good luck!
Peace! (rei)