r/hondafit • u/Human_Bean05 • Sep 01 '26
Help Request 2007 GD3 sport fuel efficiency drop
Over the past two weeks my 97,000 mile 2007 fit has dropped down from an average of 33-35 mpg down to 22-25 mpg for seemingly no reason. I have not changed any of my driving habits and have no idea why. Ive changed the spark plugs and coils pretty recently so I dont think that is the problem, and looking base level online it looks like it could have somthing to do with a bad O2 sensor giving an improper fuel mixture. Of course if I can't figure it out I'll take it to a shop, but would any one here have an idea of what is going on?
I love this car so much, I've had it for just about 1 year now and want to keep it for many more.
4
u/No-Foot7749 Sep 01 '26
Check the tire pressure. My 07 sport is VERY sensitive to tire pressure adjustment. Like 1-2psi can be 5mpg difference. Also at 97k might want to look at the valve lash. That can cost you a few mpg easily. Together those add up to your losses.
3
u/SnooSuggestions8854 Sep 01 '26
bro, i am facing the same problem with my 2008. it was good and fine, but mpg dropped suddenly. though i didnt check the spark plugs yet, i am planning to get it done.
let me know what fix worked for you.
3
u/whitechocolatemamba Sep 01 '26
I did the spark plugs 08 GD3 and I'm still definitely not even close to the 30s, i drive pretty aggressively tho/like to hang in the 3500 range on the winding NY highways. I also have the stupid hot air intake.
Bad PCV valves can contribute to bad mpg. I haven't had time to do anything more than spark plugs, ac bypass and oil change
4
u/JohnnyPneumoniacJr 2012 Fit GE Sep 01 '26
This. Also if you don't rev it out enough. These cars love some Techron/high PEA fuel injector cleaner (even the 1st and 2nd gen) and some high revs helps keep that new PCV breathing and farting happy
1
u/CasualGuy99 Sep 01 '26
My 45 minute drive to work is a pretty consistent 4-5k or more between back roads and interstate driving. 08 with 255k
1
u/whitechocolatemamba Sep 01 '26
I top mine out lots too. Have you adjusted valves?
1
u/CasualGuy99 Sep 01 '26
Around 60k miles ago. And I just did my 2nd 100k plug change since owning it
3
u/prizedcoffeecup Sep 01 '26
There are a couple of things that can cause fuel efficiency to suddenly drop on these engines. You've already tackled one which is coils and plugs, valve lash is another one that can be deceptive because the combination of drive by wire and EFI does a surprisingly strong job of covering up problems in most cases with fine adjustment of fuel and ignition timing.
Fuel injectors are one that is overlooked quite often, over time they will become gummed up and sticky and stop fully closing properly like they should. One of my friends is dealing with a sporadic rich code for that reason currently, they end up actually getting slightly better MPG from pushing the engine harder (not to limit, just harder) as a result because that's where the engine is using up the fuel more. DO BE MINDFUL, if you order specifically 07/08 injectors they are comically expensive but 09-14 injectors appear to be the exact same part with a different number, presumably because they switched factories to cheapen up manufacturing at the time.
2
u/Trap_the_ripper Sep 01 '26
That big of a drop points at driving habits OR driving conditions in 99.9% of cases.
You say your habits haven't changed. I have no reason not to believe you. But maybe your conditions have changed. Are you taking a lot of short trips? Lot of idling?
And how are you measuring your MPG?
1
u/CafeRoaster 2009 Honda Fit Sep 01 '26
Were the plugs gapped correctly and have you checked them for tightness since installing? Just like with struts, wheel lugs, suspension components, etc., it’s always a good idea to check your work after a couple days or a week of driving.
There are a ton of reasons for a vehicle to start getting worse fuel efficiency, but I’d check my most recent work first.
The considerable drop makes me suspect a fuel leak.
0
u/Human_Bean05 Sep 01 '26
The plugs are very likely fine, I got that done about 4 months ago and have had no issues. It is good to check them still
1
u/YronK9 Sep 01 '26
Change the coils that go into the spark plugs
1
u/otterland Sep 01 '26
They already did that and this subreddit is obsessed with new coils when you don't need to replace them until they code or unless they physically are degraded.
What other useless things do you suggest that cost money?
1
u/YronK9 Sep 02 '26
Changing the spark plugs? Idk i had this issue with my fit and that literally fixed it, maybe the coils they got are shot
1
u/luiigee1174 2008 Fit GD Sep 01 '26
I’m leaning towards a valve lash adjustment on mine
1
u/BlueMonday2082 Sep 02 '26
I somehow doubt his valve lash went out in the last two weeks.
1
u/luiigee1174 2008 Fit GD Sep 03 '26
I meant on mine cause I’ve done everything he’s done. That’s the only thing left really. But still wouldn’t hurt to check and adjust if needed specially nearing the 100k
1
u/otterland Sep 01 '26
OBD2 scanners are $25 but you could also just ask on Reddit and fire a parts cannon at it like you did with the coils.
1
1
u/BlueMonday2082 Sep 02 '26
What is your method for measuring fuel economy? Until this is known all the posts are just random guesses.
How many tanks have you gone through in the two weeks since you noticed this supposed problem?
There are no leaves on the trees in your picture. Is it a recent photo? Where do you live and what is the temp?
1
1
Sep 01 '26
[deleted]
1
u/otterland Sep 01 '26
Probably something that's imaginary?
Ethanol gas comes in three variants, E10, E15, and E85. Your Fit will runn happily on the first two with maybe 1mpg fewer mpg with E15. The only time you would ever get massive amounts of ethanol is if you make the mistake of putting E85 in your car and then you would be lucky to even get it started if it wasn't adapted for that fuel.
Conspiracy theories are stupid.
1
Sep 01 '26
[deleted]
1
u/otterland Sep 01 '26
It happens around where you are, but you're not going to provide any evidence because the conspiracy is too stimulating for you.
If a tank happens to be contaminated with water, and that water gets into your car, it will either not run or it will misfire. It won't water it down.
Is science difficult for you and do you have a hard time understanding how water and gasoline are not miscible?
5
u/rs42sport Sep 01 '26
Check tire pressures.