So when i first bought this car in 2007, i was pretty satisfied with the gas milage, about 35mpg hwy. After about 100k miles, it was down to 27mpg or so hwy. After 150k, maybe 24mpg, then it tanked to about 17mpg as it approaches 180k. In the city, I'm lucky to get 14mpg, which is worse than my old 4.0L jeep grand Cherokee used to get.

Been running mobil 1 since day 1, drain and fill A/T with every motor oil change.

Replaced with oem plugs and cheap coil packs at 120k. Didn't make much of a difference.

Started misfiring on #3 for a while, then across three cylinders. Would stall at stop signs, especially with a/c on until the engine warmed up. Exhaust fumes were also pretty bad. No smoke, just an apparent rich mixture.

Just adjusted the valve lashes for the first time. Intakes were all more open than spec, and exhaust were all slightly closed. Adjusted to 0.06/0.10. Checked again after a few full turns.

Cleaned and gapped the plugs to 0.44, a few of which were way off, like 0.75. New Hitachi coil packs.

Replaced upstream O2 sensor, coolant temperature sensor, drained and filled radiator, replaced with 185° thermostat, oil change, tranny fluid, did idle reset procedure. Added lucas and seafoam to gas tank, as i do with every oil change.

The misfires are gone, no error codes anymore, and the engine has a lot more pep without stalling. the bad fumes are gone too. Pretty happy about that but surprised my gas milage still sucks.

Getting 15mpg city (up from 14) and hwy went from 17 to 21mpg.

Only thing left (i think) is MAP sensor, which is on the way. Haven't done a vacuum leak check, but reads anywhere between around 27KPa at idle to up to 96 under acceleration.

Any ideas how to get back to 30mpg hwy? Am i being unrealistic for an almost 13-year old 180k-mile workhorse?

 

There's definitely something wrong. The car should still be totally capable of better mpg, I'm not sure what is wrong though. The cheapo coil packs may be an issue?

Wait, why are you putting seafoam in the gas tank? And Lucas? That's a lot of snake oil in your gas.

 

Was recommended by my old mechanic, who told me to do it with each oil change

 

Yeah, I would stop doing that. I worry that much sea foam through your engine over the years has done some real damage.

 

Ok, I'll take the bait lol

One can every 10k-mile oil change is "that much?" I doubt it. It's just kerosene. Lower octane, that's about the only difference with gasoline. I really, really doubt it has "done some real damage." Ethanol also has a lower octane than gasoline. I don't think it causes any damage to passenger cars either. I don't think the can of seafoam with every oil change is the culprit.

After i started running it all the time (yes, every single time i fill up the jerry can) in all my 2-stoke and 4-stroke lawn equipment, chainsaws, and other small engines, I've had no more problems with the carbs. Everything starts up on the first pull. And no "real damage" either, as some of that equipment is older than my car.

There's a bunch of videos you can look up doing real world tests of seafoam in fuel as well as in the oil. Before and after, cracking open the engine, ripping apart oil filters, testing fuel injectors independently, etc. Proof is in the pudding. The same goes for Lucas fuel treatment as well.

But i digress...

If anyone has any ideas about my milage (that doesn't have to do with what fuel additives I'm adding every 10k miles), I'd like to hear them.

If anything has the potential to have done some real damage to my car, it's driving like i stole it while towing 1000-lb loads of concrete, gravel, compost, tile, granite, kegs, appliances, pianos, boats, and a few other things that look ridiculous behind a Honda Fit in 98° Florida summers with a broken radiator fan.

i abused my baby and she did everything i asked, served me well, but i retired her from towing anything more than a wheelbarrow or ladder after i got a TDI a few years ago to do the heavy lifting. I really am not too worried about the seafoam lol

 

I'm assuming that this is a typo but if not your valve lash is a bit out of spec.

Specs should be listed on a label under the hood but just in case they aren't, here they are below.

Intake: 0.15-0.19 mm (0.006-0.007 in.)
Exhaust: 0.26-0.30 mm (0.010-0.012 in.)

Otherwise, I'm a scratching my head a bit to why you're getting such poor fuel economy. Thinking out loud here...

Is the CEL engine light on and if so, what codes?

Have you checked for sticking brakes?

Have you checked the throttle body for any build up that could prevent it from fully closing or sticking (in reference to stalling concern)?

Have you checked for a clogged catalytic converter?

 

Yes, thanks for the correction on valve lash clearances: 0.006/0.010".

The only codes i had were the misfires, which were cleared up by regapping the plugs, new coil packs, and valve job. It started with one, then three cylinders. I believe the gapping on the oem plugs was the issue, maybe valves.

Throttle body was clean as a whistle after hot soak with... You guessed it: seafoam throttle body cleaner. The puff of white smoke was strangely satisfying.

So the MAP sensor arrived and i dropped it in. I wasn't very optimistic but my milage immediately started to rise! PROBLEM SOLVED! I wish i would have started with the MAP sensor. I peeked in the old one and saw shiny black debris/fouling. When i get a chance I'll cut it open and see what's up.

While everyone's car will have a unique set of issues, i would highly recommend starting with the MAP sensor for anyone having low milage issues, as that was, without a doubt, the main culprit in my case.

The screw holding the MAP sensor was stuck, however, and broke several hardened Phillips bits on my impactor. Couldn't torch it because the sensor and upper throttle body are plastic. A solid "tap" with a hammer on the back of a screwdriver did the trick to loosen the screw.

Fwiw, i was getting ~27kPa pressure at idle (with engine fully warmed up) before changing out the MAP sensor. After i was getting ~38kPa.

I should mention that i have a washable k&m air filter that i installed at the first oil change. I didn't realize i was supposed to oil it after cleaning it until recently. Oops. i do expose my car to a lot of dusty environments: landfill, off-road on dirt roads hunting, beach driving, etc. The car has also lived outside for 13 years in a high humidity climate. Not sure if that has much to do with a bad MAP sensor, but just sayin'.

The other things that i did all helped to restore performance, but had minimal impact on improving mileage. One thing i left out in the original post was that i cleaned the EGR a few months ago. That didn't help either. Now maybe i wouldn't be getting the miles I'm getting now had i not done all those other things, but definitely the MAP sensor is what i would have started with if i were to do it all over again. I certainly don't regret doing the tune-up.

One last bit of advice is that if you plan to change the PCV, do it when you do the valves while you have the upper intake manifold removed. You'll have to pull the lower intake manifold too, but everything else will already be out of the way. i was going to change mine but just realized where it was. Problem solved, so just going to return it to amazon.

Here's a screenshot of me hitting over 30mpg in city/suburban driving (for the first time in years) after a $17 one-screw fix. Can't wait to take her on the highway! Woohoo!

 

Congrats on getting it figured out, fellow central floridian!

 

Represent!

 

Thanks for the info about cleaning the M.A.P. sensor!!! Cleaned it today because I was only getting 22.7 miles per gallon in full city driving. After cleaning with appropriate spray cleaner and cleaning the electronic connections on that sensor with electronic spray cleaner, I now, immediately am getting 25.8 m.p.g.! That is now acceptable for me. Couldn't figure out why my city mileage was so bad for such a small car but this was an answer for me. Anxious to check my full highway mileage now. Thanks for posting that info.

 

25.8 is still way too low in city driving. I do a TON of city driving (in a cold climate to boot) and I still average above 30.

 

I'm pretty happy with that. Considering that my driving is complete city driving. Constant stop and go, stop and go, no freeway/highway mixed in. My original window sticker states that the city driving should be 27 with an "expected range" for most drivers of 22 to 32 mpg. All comes down to how you drive I guess and the conditions. Sure, I'd love higher but I'm just glad that I'm approaching the median range.

 

Hmm I'm debating on taking a look at this. For the longest, I could only get 240 miles MAXED on a tank no matter how gentle I was on the throttle.

 

It's really worth it if you have never cleaned yours. My car is a 2010 with about 120K and the M.A.P. sensor never was cleaned to the best of my knowledge. And for what it's worth, I've read that that sensor is good for the life of the car, but it must be kept clean. Good luck, hope it helps.

 

How many gallons are you putting in? If you're only putting in 8 gallons, that's 30 MPG.

Distance between fill ups is not a useful metric.

 

I have two basic questions: Does the 2007 Fit have a MAF and a MAP sensor. Where are they located?

 

When i searched for parts i could only find a MAP sensor, although my ODB-II app shows me MAP and MAF data.

it's on top near the windshield on the back of the throttle body.

Mine wasn't throwing error codes, but it was definitely off (not accurate). I kept the old one. Maybe I'll try cleaning it and testing it against the new one. For under US$20, i opted to just replace it.

 

Me too. I'll take what i can get. In pure city stop n go, I've been averaging around 22-23mph, around 30 in mixed suburban driving. Compared to the 14-17mpg i was getting, it's outstanding.

The EPA estimates also take into account certain credits for clean air tech, I believe, so it's not a number that reflects actual mpg. Maybe "debits" for dirty exhaust is why my TDI is rated for 38mpg hwy but easily gets 50mpg.

This may be my beater car, but i definitely plan to drive it until the wheels fall off, and then some. While i may not be getting top mpg compared to similar vintage/milage Fits, every month i drive this thing is another month I don't have to make a car payment.

Just for the sake of crunching the numbers, say i *could* get 27mpg city, that's 5mpg more than I'm getting x 10 gallons/tank x maybe 2 tanks/month = 100 miles/month ÷ 22mpg = 4.5 gallons/month * $2.24/gallon = $10.08/month. Even at my old, crappy, pre-fix mileage (14mpg), it was $32/month. Even if i drove double the miles (4 tanks), that's still just $64/month, worst case. That ain't much compared to $500/month or more for a car payment! I can live with that.

 

My 2007 Fit Sport AT averages 19/20 mpg with all the hills and stop signs of San Francisco. Pure city driving.

I've felt it could do better. I inherited the car from my parents, who rarely drove it. When I got it in 2014, the car had only 5k miles on the odometer and drove poorly. Mileage was only 15 mpg. I have changed the major fluids twice in the past five years, run fuel cleaners, etc. The car runs very well now, but the mpg's are still low. Gas is expensive in SF @ $3.90/gallon. Yet I only spent $30 to fill up today. I only fill up once a month on average.

In contrast, my 2017 Fit 6 speed averages 28 mpg's in the city.

After you listed all your steps in a process of elimination, it was nice come upon a possible source of the low mpg's. A MAP sensor is on order and will be swapped out. I'll retain the old one and clean it.

I wonder if the MAF sensor, if it exists, is hiding in the vicinity of the air filter housing?

 

Nothing to add on the mileage issue, but the Fit does have MAP (Manifold Pressure) and MAF (Mass Air Flow) sensors. The MAP is right at the top of the inlet to manifold just past the throttle body. The MAF is right at the beginning of the intake tube coming from the airbox. It actually looks like it is on top of the box. Both are easy to get to and replace/clean. I don't know if cleaning the MAP really has much impact, but if the MAF is very dirty, cleaning it can increase mileage as well as driveability.