High mileage maintenance questions
 

So I have an 07 Fit Sport with an automatic and 220k miles on it. I've owned this vehicle for the last 95k miles or so. Between about 130k-140k miles I flushed the coolant and did a valve adjustment. Other than that, it's just been tires, oil, air filter, and brakes. The car hasn't given me any problems to speak of but I've been noticing the fuel economy steadily dropping over the last 40k miles or so. My daily trip to work is about a 55 mile round trip consisting of mostly 45-55mph roads and this hasn't changed since I've owned the car.

When I first bought it, the car usually got 33-35mpg and now 30mpg is about as good as I'll ever get. If I drive the majority of the entire tank on a non-stop interstate run at around 75mph, I'll get maybe 31-32mpg now with or without the AC on. I suspect something needs attention but without the car really complaining, I'm not exactly sure what to fix. Love Honda's....not sure what to fix because everything works.

CV axles are probably going to get changed in the near future as I recently started getting a slight vibration when accelerating uphill but it's very minor at the moment.

My first thought is fuel ethanol content.

We are in the summer months and they are adding the maximum ethanol to the fuel. Your mileage drop may just be due to the ethanol content.

Before you spend any money on things like new 02 sensors or a new catalytic converter, I'd run a tank dry and fill with non-ethanol fuel and see what the mileage looks like with it. Here's a site that lists pure fuel stations. I see one in your town.

https://www.pure-gas.org/?stateprov=GA

If that doesn't make a difference, I would then look at doing another valve adjustment along with a spark plug change. At about 65k since your last service, they are probably due again. Especially since it's a higher mile car.

I'll look into the plugs since I can't remember when I changed those last. I know I've at least looked at them but it's been a while and can't remember if I actually changed them at that time. The mpg's have been steadily dropping little by little over the past 5 years so I don't think ethanol content is the culprit here.

The valve adjustment is probably about due again as well. I don't think I've changed the auto tranny fluid...might need some attention.

Spark plugs can definitely make a difference! Good luck!

For sure...I bet that will increase your MPG.:nod: Of course, you also need to inspect or replace those spark plugs.


Can you discern any slight idle roughness with a cold engine or under acceleration? (Hold your hand under the tailpipe.) If so, at your mileage, you MAY have weak ignition coils.



PS, you didn't mention ever changing your cabin filter....:iough:

Could this potentially be a coilpack issue?
The minor vibration under load could be the beginnings of misfiring?

I did my coilpacks and spark plugs, and the car immediately became a lot smoother. Can't say my mileage got sustainably-better though, as I also put in the Progress RSB and Enkei RPF1s around the same time (so my right foot has gotten heavier as the car has become more tossable). The first tank did seem to yield ~10% improvement.

I recently saw a decline in fuel efficiency, and also note some (what feels like a misfire) stuttering at low rpm.
Cleaned the MAP sensor with isopropyl alcohol from the local pharmacy, and have seen a 20% increase in fuel efficiency on the same driving route, with the same fuel.
5 minute job, including figuring out where the sensor is and how to get to it. :thumbups:

Not saying this will change your situation, but the MAP or MAF sensors are often seen as non-service items in regulator maintenance, but they make a major difference when they don't measure accurately.
This was on a GD1 L13A engine, the 2007 Honda Jazz(Fit) 1.4 DSi.

I really like how the car runs with Denso Iridium TT plugs.