I have a 2007 Fit Sport AT and recently I have been getting low MPGs. After changing the spark plugs, doing the valve adjustment, two oil changes, new tires with complete service and a new air filter (K&N this time) I haven't been able to obtain more than 27MPG per tank in three months (19 being the lowest). I have read that the coils on these cars can go bad really fast, but so far I never had the Check Engine light come on. So far the coils are the only thing that I haven't changed on the car, but spending $200 on something that I am not sure is wrong doesn't seem right.

Is there some way to test the coils? Can changing the coils improve the MPG of my car? Does someone have a similar experience?

 

How many miles? Did you use the iridium Denso or NGK plugs or something else?

Mixed feeling on the K&N air filter. Some folks claim an increase in HP and mileage, but others claim that the oil used on the filter gets into places where it shouldn't and can cause all sorts of problems. For this reason, I've stuck with traditional air filters and replace them religiously.

 

The car just hit the 130k. I put 4 NGK Iridium as it says on the manual. I choose the K&N air filter because there is a lot of dust where I live, and a paper air filter doesn't last long. That's why I prefer to use these filters instead of paper so I can clean them instead of changing it every 3/6 months. I just checked the coils and it seems that 2 of them are not even red anymore, more close to a light orange.

 

Yup, you'll want to replace the coils. You could wait until they go completely, but that takes the risk that when one goes, the rest will follow very soon after, and getting the car to run might be a challenge. I recommend the OEM Hitachi coilpacks, number ending in 0053. About $200 a set at rockauto last I checked.

 

I've changed my spark plugs to the OEM denso's, did the valve adjust and recently change my O2 sensor. Still getting around 25 mpg a tank. Lemme know if this solves your problem.

 

Make sure the IAT sensor is reading correctly, when they get old they read low which will make things run rich..

I have a diagnostic OBD dongle from Bosche that lets me see whats happening on the engine with my Iphone. There are similar options out there..

Also if your thermostat is stuck open your mileage will suck too..

Cheers.

 

Just ordered 4 coil packs for $200 on RockAuto and it should arrive on Wednesday at most. I'll let you know if there is any improvement

Cool, I may buy one if necessary. Thanks.

 

The "real" mileage is 27-28 mpg based on 2008 revised guidelines (https://www.fueleconomy.gov/feg/noframes/22860.shtml)
87 Tercel with same engine displacement has better mileage, but its body is about 600 pounds lighter.
So unless you are using nitro-methane or aviation fuel (which will destroy an engine due to the insane temperatures), don't expect fit to be a super gas miser.
(I don't want to hear response from someone who is driving empty country roads, I am talking about city driving !!!)
So:
any aftermarket items on the intake will change the gas mileage (both ways)
using ethanol added, clean burning fuel as well as cheaper gas will decrease gas mileage.
For a time being I was using ARCO or related cheap gas and on all cars I have had. All cars were a bit slow to start and used more gas than advertised.
Now back to original topic.
Also plugged catalyst, not fully seated EGR with rusted seat or cracked exhaust header can decrease fuel economy by about 2 mpg
If coils are in question, they can be checked with the scope using adapter between the coil and a plug (never personally shopped for this one though)
I am getting 28-29 mpg on city streets with light to moderate traffic (catching about every second green light en route) with ambient between 60 and 75, 25 to 30 minutes each way (14 mi distance)

 

I ordered the 4 coils yesterday at RockAuto, they should arrive on Wednesday. I'll let you know if it works. After reading some of the replies here I may work on the IAT or clean the EGR depending on what happens after changing the coils.

 

Pardon my ignorance, but what's an IAT?

 

Intake air temperature sensor, mounted in air cleaner housing, it's thermistor that works same way as coolant theremo sensor

 

Only Denso or NGK spark plugs work ! My car gives about 25 mpg since I bought it.

 

Weird. I'm starting to think these guys getting 38 mpg live one block away from the highway and make a daily trips on it! For those of us that live in the city with stop and go we are stuck at 25...

 

I'm getting 28 with a 50/50 city street/freeway 16 mile round trip with Bosch Iridium plugs..

 

I get about 30 mpg easy driving. A full tank will get me right around 310 miles and that's when the needle is well on the "E". 204,xxx miles 5spd 100% stock. Just changed my plugs to oem and brand new oem filter. My car stalls on cold climate without a proper warm up so I suspect i need a valve adjustment soon. After warm up, it drives fine.

 

BTe don't know how widespread it is, but the EPA has a time table to raise the Ethanol content in fuel over the next few years, as I get it, this year we go to 15% which WILL result in a decrease in mileage in all gas vehicles. Ethanol has less btu's of energy than gasoline so as they increase the content the mileage goes down. simple physics.. I hate biofuels.. arg.

 

So far so good, my two last fills returned 26MPG with a drving of both highway and city (50/50). I am going to travel this weekend so I should get a higher MPG. I will give an updated on Sunday probably.

These were the last fill-ups in my car before changing the coils. I use aCar to keep track on everything on my car. From November of the past year the highest MPG was 25.7.

 

Tight valves (to some extend) cause longer intake/exhaust times which result in far better performance at high end of engine rpms (most "hot rods" are barely idle but have high performance on the race track!)

 

Thats cool to know. Too bad my fit is not made for high performance lol