My first car was a '93 Civic EX coupe which I bought new. For the 8 years and 218,000 miles I owned it, I always got highway mileage between 35 and 40 MPG. Two years ago, I bought my wife a '96 Civic EX coupe (engine D16Y8). I have maintained it pretty well, including replacing the timing belt, drive belts, oxygen sensor, and exhaust manifold. I also installed a K&N air filter. The car drives great; however, since I got it, it has gotten about 27 MPG highway. Until fuel passed $3/gallon, I didn't worry about that too much. Now it's time to research the problem. Last week, I moved from Florida to Colorado. I never got around to addressing the mileage issue before making the 2000-mile drive, stupid, but I did track my fuel mileage all the way up, to give me a baseline for investigating the problem now that I'm up here. As expected, I got 27 MPG all the way to Texas. However, once I got to the high plains (climbing from 600 ft AGL in Ft. Worthto 3600 in Amarillo), my mileage jumped to 33 MPG, even though I continued blasting the AC.

So, here are my questions:
1. What should I investigate to locate the cause of poor mileage? Valve adjustment?
2. Isamajorimprovement in fuel mileage at high altitude normal? Is it somehow indicative of what was causing my poor mileage before?

Thanks!
Billy Andrews

 

Check your spark timing. This seems likely since it had the same performance ever since you got it.

I don't think the '96-99 were ever quite as good on mileage as the 5th generation ones ('92 to '95) were though.

 

Ive done every tune up i can, and i get the exact same thing you do. let me know if you figure it out. how much mpg do you get in the city? i get around 24

 

Someone recently posted on the forum a similar problem with a 5th generation Civic. The problem turned out to be a bad PCV. I can't say I really understand why this would be so, but there you are.

 

Interesting, do you have a link to the thread? the pcv is the only thing i havent replaced yet

 

Sorry I don't remember the link. If I find it, I'll post. In the meantime:

 

I still haven't found the thread, but an answer found on WikiAnswers seems to make sense:

"A stuck-open PCV valve will allow unmetered vacuum to cause a lean air/fuel mixture. The engine management system will "fatten-up" the fuel injection spray time (volume of fuel) to compensate for a lean air/fuel ration, thus using more fuel to accomplish the same task. It can cost you at the pump & cost you in damaged engine-related repairs. Change your air filter every 10K miles & your PCV valve every 25K miles."

http://wiki.answers.com/Q/Would_a_ba...or_gas_mileage

Other good PCV information:

http://www.tegger.com/hondafaq/pcv-replace/index.html

http://www.civicland.com/forum/gener...ot-damage.html

 

the thing is, newer civics have more power than older ones, and of course more power requires more fuel

 

My '97 DX Coupe (D16Y7) consistently gets 35-38 mpg and that's even with fairly spirited driving. Your EX shouldn't be much worse than that unless you're flooring it all the time with the a/c on full blast. Try the PCV valve fix and check your timing as mentioned above.

 

well if both where EXs the newer one is only what 2 hp more.

but one thing that wasnt said..... what are the cars? 5speed manual or automatic?
a 5speed will get sweet milage, a automatic will give ya a drop..... my 94ex 5speed got about 35mpg all the time, and my 99ex automatic only gets like 29mpg all the time.... maybe more if im cruising on a road trip..... but the AC also effects milage greatly.