Hey everyone. First time poster, long time lurker/researcher and long time Japanese car owner/mechanic/modder. Looking for some advice.


The car: 1999 Civic EX, auto
The problem: getting around 23 mpg

What I've done so far:
-replaced entire distributor, set ignition timing
-spark plugs
-spark plug wires
-O2 sensor
-Fuel filter
-Set valve lash (.007/.009)
-Checked IAT sensor
-Checked TPS sensor
-Checked timing belt position
-Checked cat for clogs
-Compression test (all ~185psi)

Everything checks out okay, all the sensors are within factory specs. Yet the car gets 21-23 mpg around town, every fill up. I had a 98 Civic DX before this that I drove way harder (old beater) and consistently got 28-30 mpg.

Is there anything I haven't checked that you guys could recommend? I'm out of ideas.

 

Sadly, this^ city mileage is not unusual for Civic autos.

Is the transmission shifting smoothly?

 

The transmission seems to be shifting fine. The last Civic mileage of 28-30 was city driving too, and also an auto. On the highway I got 38-40.

 

Different car or same car as in OP?

 

Different. Used to have a 98 Civic DX auto with i/h/e, now I have a 99 Civic EX auto, i/h/e. I know they're different cars and slightly different engines, but close on 8-10 mpg just seems crazy.

 

The D16Y7 will get better mileage than the D16Y8. The former emphasizes fuel economy whereas the latter places a bit more emphasis on performance.

I have seen my 00 Civic coupe EX auto get similar city mileage to what you report. On the hwy, it will average 31-33.mpg.

 

Inflate your tires to 38psi and recheck your figures.

My built b20 get 34hwy doing 80mph. City about 20ish +/- 2

 

I got em at 42psi.

 

Haha... this^ high inflation pressure may be unsafe.

 

Drop in an auto transmission, and let's see where your mileage (and power) go.

 

They're well within the max inflation range.

 

What tires, brand and size? Are you also considering safe pressure limits for the valve stems?

 

Max sidewall psi is 45, I run mine at 40 psi. Honda set the door sticker psi to maximize the "lush" ride. 30psi is the honda sticker spec

I recommend max sidewall psi +/- 5% max/min

With low rolling resistance Michelin defender tires I am getting 40 mpg city with my 5 speed. I'm on the hx 14's

With the correct tires a civic coupe auto should see 32mpg without much effort. Tires and tire pressure make a huge difference

I can show you my gasoline consumption data logs for the past year if I haven't convinced you yet.

 

Post your details - car, tires, size, type of driving, etc. I'm all about data.

 

1996 civic hx / 1998 camaro ss
Michelin defender low rolling resistance tires
short ram intake
iridium plugs
vacuum gauge
[SIGPIC][/SIGPIC]
My civic thread

Daily commute: 3 school zones, 6 stop lights, 45mph, 4 times daily. :turtle:




Sorry drove my truck this winter it was snowy and rainy in dallas. Not exactly a years worth of data

 

Haha...your HX-CVT disqualifies you from this mpg thread.

What tire size?

 

5 speed non auto but yes it technically does anyways. tires make a huge difference

I don't remember tire size stock? 14's on my light weight factory enkei wheels

 

Tell me the basis and context of these^ statements.

 

If op is running tires sized above OE spec (for whatever reason he might be) and they are improperly inflated he would be perceived into thinking that A) his mileage is crap due to the VSS reading low=odometer turning slower and B) more rolling resistance equates to higher load on engine thus wasting that much more fuel.

IF OP is running correct tire/rim specs, and tires are properly inflated, this is a moot point.

 

The only other thing that I could see needing to be done would be cleaning of the fuel injectors...OP how many miles are on your engine?

 

http://www.tirerack.com/tires/tests/...y.jsp?ttid=121

I will admit after reviewing fuel logs for other automatic civics vary vastly and city driving absolutely destroys any gas mileage.

I've never driven an automatic civic, but good god 24 mpg is what my ford fusion gets with its 2.5 liter 4 cylinder in the city and it weighs like 3800 lbs. they must have really tweaked auto trannys since the late 90's. Even the fuel logs for the automatic cars with guys running all highway top out at 34-36 mpg with a few mid to high 20 tanks in the mix

I change my statement, I don't think I could put up with 24 mpg. How does a 1.6 even do that?


For reference my boring commuter car

Efficiency log for: Boring - 2011 Ford Fusion Sel
Lifetime Fuel Economy: 23.9 mpg (US), 9.8 L/100 km, 28.7 mpg (Imp)
90-day Fuel Economy: 21.9 mpg (US), 10.8 L/100 km, 26.3 mpg (Imp)
3-tank Fuel Economy: 21.8 mpg (US), 10.8 L/100 km, 26.1 mpg (Imp)
EPA Combined Rating / % over rating: 27 mpg (US) / -19% (based on 90-day fuel economy)
Total fills: 12
Total fuel used: 181.46 gal (US), 686.9 L
Total distance traveled: 4333.7 mi. / 6974.4 km
Average tank distance: 361.1 mi. / 581.2 km

 

That mileage is normal. Remember in addition to the engine being a little more performance oriented than a Y7 the car is also heavier being an EX. Civics get great fuel mileage, but only with a manual trans.

 

I'm sure gas that have 10% ethanol plays a part in low mpg as well as the automatic, the automatic, from what I see, requires a little more engine work to get the wheels turning but once cruising its fine. The city mpg will suffer and will vary because of the constant stop and go at red lights which causes your engine to work more to get it up to speed everytime you leave the red light.