Greetings, hopefully I can figure out what is going on. I've read a bunch of different things about this but it doesn't make any sense to me. I am the original owner of the 2007 Accord EX-:L 4 cyl. I've never got anything better than 28 mpg with this car. Most of the time it's 27 on the highway. I just replaced the plugs at 180k because after having the airbag recall completed the dealer said the rough idle was because of the plugs. Now I'm getting 23 mpg on the highway and I replaced the plugs with the OEM NGK iridium plugs and it still idles very rough. I was shocked when we bought the car new at how low the gas mileage was coming from owning a VW GTI VR6 that would consistently get 32 mpg on the highway.

Any ideas?

Thanks

 

Did the car originally come with the plugs you put in? If not, switch to the OEM spec plug.

FWIW, I find your reported mileage surprisingly low, especially for a four cylinder model; I'm thinking you should easily be able to get over 30 mpg on highway only trips.

 

As far as I can tell they were the OEM plugs. They were NGK Iridium. The car has never achieved 30 mpg on the highway since day one.
Thanks for your reply.

 

I guess I need to rephrase the question; just because you replaced NGK Iridiums with NGK Iridiums does not mean they are the same plug. Where did you get the plugs and are they the correct heat range (i.e. model number)?

 

I bought the plugs at Advance Auto. They were NGK Laser Iridium Spark Plugs 6994 w/o SULEV [Federal Emissions]; Gap 0.044".
Hope that helps.
Thanks!

 

Okay, correct plugs, have you had the OBD-II codes read?

 

I didn't check the codes because there isn't a light on. I will check for codes when I get off work today.

 

I just checked and there aren't any codes at all.

 

Next step, make sure all wiring to sensors and such (especially thing like O2 sensors) are properly plugged in and that all vacuum lines are properly attached.

 

when was the last time you did a compression test?

 

I have never done a compression test. The car drives fine. Maybe I am just expecting too much. I connected my OBD-II reader to log my commute to work this morning and it said I got 39 mpg. It's about a 35 mile trip up the highway at 65 mph.

 

Hmmm, 39 mpg is about what I would expect (hence my earlier comment about 28 being low). FWIW, my third generation TL is essentially the same car as your seventh generation Accord (built off the same platform and on the same assembly line), and I routinely get 32 mpg in it on the highway; my best being a 35 mpg average on an 1,100 mile stretch between northern Indiana and Denver, Colorado.

 

This car is only rated to get 32 maximum mpg and I've never seen that. I know I'm not getting 39 because the math says 24. The TL is a 6 cyl isn't it? They get better gas mileage. My father in law had one.

 

By definition, the cars with the 4-cylinder engines will get better fuel economy.

How do you know the math says 24 mpg?

 

Well, by real life example my 2002 VW GTI VR6 got better gas mileage that this 4 cyl Accord. My father in laws Acura TL got better mileage.So that is what I am comparing it too. Not the EPA measure, real life.
What do you mean how do I know the math says 24? Miles driven, fuel used= mpg.

 

Sorry no, your real world examples are not even remotely comparable. If you want to do a true comparison, you'd need to compare a 4-cylinder Accord with a 6-cylinder Accord, comparing to an old GTI which is both smaller and lighter makes no sense.

Then there is the question about how you calculate your fuel economy; unless you're adding together all of the miles driven from at least three consecutive full tanks of fuel and then divided those miles by the sum of the gallons of fuel you put in at the gas stations, then your calculations will not be terribly accurate. Given my experience with Honda OBD-II cars, I'd say it is an odds on bet the 39 reported for your car is a heck of a lot more accurate than the 24 you're reporting.

 

FYI, the 2002 VW GTI VR6 has a gross weight of 3929 lbs. The 2007 Honda Accord 2.4 cylinder is 3250 lbs.

 

LOL, NOT! "NOT" as in, you are NOT comparing apples-to-apples.

The weight of a 2002 GTI VR6 was 3,011 pounds. FWIW, the "Gross Weight" of a vehicle is how much it is rated to weigh when full of passengers and cargo.

 

My Accord weighs 3250. It's heavier. Is that understandable?

 

Once and for all, the Accord is heavier than the GTI, I've said that three times now; are you finally of the understanding the GTI is the lighter of the two cars?

 

My 2008 2.4L was getting 35+ MPG on the highway with HORRIBLE plugs.
My 2005 3.0L got about 30 MPG on the highway, no matter what shape the plugs were in.