Hi, my 1997 Honda Civic HX SOHC 1.6cc (130K mileage) get really poor gas mileage. I got the car a few months ago. At first I got a total of 250 miles per 9 gallon. Now it drop to 200 miles or less per 9 gallon. So I started to do a bunch of things such as:

1. Changed the Spark plugs and wire set.
2. Checked the distributor caps and rotor and ignition coil. They are in really good shape.
3. Have the fuel injectors serviced at auto repair shop.
4. Replaced the fuel filter.
5. Changed the transmission fluid. The Honda dealer told me that I only need 3 Qt. of fluid but I used up to 4.5 Qt. to bring the fluid up to the desired level. Which is weird and the fluid that I drained out was more than 4 Qt. too.
6. The car doesn't seem like running rich as I didn't smell any gas coming out from the exhaust.
7. The air filter is a little bit dirty but I don't think it is going to effect so much. I ordered a new one online and I am still waiting for it.

Yet the gas mileage is still the same and shows no improvement. Now I am out of idea what is really wrong. The engine sounds and runs smooth. What could have cause such a huge drop in gas mileage. My friend's 1995 Honda civic DX can get 260 MPG in the city and 330 MPG in the highway. Mine was falling behind so much.

 

Here are a few things to think about:

• Do you have a check engine light? Does your check engine light work? (Should turn on at startup and then turn off.)

• Do you have a lot of extra weight in the car, like a big box of subwoofers in the trunk?

• What is your driving style like? Do you drive fast everywhere or do you take it nice and easy? Do you brake a lot? Are there a lot of hills where you live? Do you do more in city driving or more highway driving?

There are many factors that can change your fuel economy. Even something small like properly inflated tires can help just a little.

 

Thanks for reply, WellFedHobo.

1. The engine light didn't turn on, but it is working.

2. I have very little items in the car and everything is original.

3. I drive easy. Hit the gas steadily and always maintain at the same MPH and RPM (1750 - 2000 rpm and 40mph). I live in a okay size town. I do brakes quite a bit, but every time at Red traffic light, I free the gear, let the car slides and break steadily. Try to be as fuel economy as possible.

Compared to other friends' civic in the same town. My civic get a really bad gas mileage. What else can I think of?

 

Anybody has any idea how much gas mileage does your Honda Civic closes to 1997 year and 130k mileage get? I am just wondering if it is because of my car is old and that's is what mostly happen to a car at that age?

I have read a post by simons81 with the tittle "Low fuel economy?". After a lot that he went through, the problem was not fixed.

Below is the things that he had done. I copied it from his post and sorry that I don't know how to do the quoting in this forum.

- Mobil1 fully synthetic 5w20
- K&N oil filter
- NGK spark plugs
- new plug wires
- new rotor / distributor cap
- seafoam treatment (in vacuum tube, crankcase and gas tank)
- new PCV valve
- new air filter
- cleaned IACV (which is still acting a little lazy, maybe needs replacement)
- set timing (while CEL was triggered)
- checked tire pressure
- pulled spark plugs after leaving ignition at II; could not see any excess fuel
- checked all tubes I could see from above and below the car
- checked as much of the exhaust line as I could and found a hole in the muffler pipe (before it reaches the muffler, about the diameter or a dime)

So, I know I can't relate the problem that his car had will be the same with mine. But I just wanted to narrow down the possible myth to the poor gas mileage problem.

Here is what I though, as he mentioned that his car got tick tick tick sounds when starting the engine at cold temperature. Well, this is similar to mine. It could be the valves clearance is not correct and which is the thing that he didn't tried to get his gas mileage boosted up. Should I go and fix my valves clearance? How much will this cost?

Another thing is that my temperature reading is only about 1/4 the max (before reaching the red line). Is my engine thermometer's reading is too low and not functioning properly, which lead to faulty fuel adjustment into the cylinders?

One last thing that I would like to ask. When I replaced my fuel filter last time, I started the engine, then I went down to the fuse box below my steering and unplug the fuel pump's fuse. The car died right away. Isn't that it was supposed to die when the gas in the fuel filter dry out? Or was it because of my fuel pump generate not enough pressure in the tank?

 

It would die due to the lack of fuel pressure.

MY d16y7 just got 32mpg at 114k miles. It also has the valve tick. It is possible that the engine temp reading is throwing off your mileage. There are a few other things that can mess up mileage. O2 sensors for one, but they usually throw a CEL code (check engine light). Catalytic converters can get clogged up over time and possibly cause poor fuel economy. I'm not sure what else. It seems like you've replaced all of the usual suspects.

 

Replace the thermostat. The engine must warm up properly or the ECU will not operate in closed loop mode. While it is below normal temperature the ECU runs it richer and it will waste gas.

Also check/adjust the timing with a timing light. If the spark timing is late the engine will still run smoothly, but very inefficiently. Both power and mileage will suffer.

Both of these situations are common reasons that reduce gas mileage, but don't make the engine run badly or turn the CEL on.

 

also, no one mentioned anything about the pcv valve. there is a test. when the car is idling, pinch the hose. if you hear a click, then the pcv valve is still working. if not, you need to replace it. the hose is easiest to pinch from under the car.

 

Thanks for all of the replies. I will try to do what is suggested, but it may take some times before I will tell you what is the result. It is the end of the semester and school is getting extremely busy, haha.

 

Okay. I am done with the PCV and also the air filter changed. The result is 2mpg improvement, which bring it from 23mpg to 25mpg. Now my next plans are the catalytic converter and thermostat change, valve clearance adjustment, and ignition timing check. I noticed some rattle sounds inside the catalytic converter a few days ago. But, the sound is gone now. I guess the exhaust had sent the metal piece out.

For the catalytic converter (CC), it looks really old and rusty. I am sure the ex-owner changed it before because it doesn't look original. I found two cheapest CC online in ebay. I know, for reliable part, I shouldn't use stuff from there. But check them out:

http://cgi.ebay.com/ebaymotors/ws/eB...AQ:MOTORS:1123

and

http://cgi.ebay.com/ebaymotors/ws/eB...AQ:MOTORS:1123

The first one does have limited lifetime warranty. So I might go for it. But, my question is, do I need to get a gasket for the CC outlet that is connected to the exhaust? I couldn't find the info for that part. And also. isn't that the ECL will turn on if the CC is bad? My ECL is working as last time when I forgot to plug the air intake sensor back, it turned on.

The jobs for valve clearance adjustment and thermostat change are okay. I am totally sure that I can get them done easily.

For the ignition timing part. I need some opinions. Some says that I need to get a timing gun for that. But, I was thinking since I pope up the valve cover to perform the valve adjustment works, which I know exactly when each piston is at its TDC position. I can take this opportunity to verify if the crackshaft pulley is at its TDC mark when the upper timing sprocket is at its TDC. Then, I can make a mark on the distributor housing for the first ignition output. And, check if the distributor rotor is pointing at the first output too. Is this good enough to perform ignition timing check?

 

If you're getting decent performance and CEL is not on, catalytic converter should be OK. You can remove it from the car and inspect. If it's not melted inside you should be able to see all the way through the small holes in it from one end to the other.

No your idea on timing is not good enough. You need a timing gun. The exact moment the spark will fire is determined in part by an electronic delay in the ECU, you can't inspect it mechanically. Borrow a timing gun or buy a cheap one from a parts store. The occasional user doesn't need the fancier ones.