1989 Civic, massive economy drop, question.

Gary Palmer · 12-04-2006, 04:44 PM

Hello everyone:

I have a very perplexing dilemna. I had just managed to finally get my car to give me 37 mpg. However, the next tank, the first 1/2 of tank seemed to do very well, but the second 1/2 seemed horrible. The tank I just finished was profoundly, substantially worse. This tank was down under 30 mpg.

I am not getting a CEL indicating any problem of any kind. Does anybody have any suggestions or thought's on what I might check? I have a VM monitoring the Oxygen sensor, and the sensor seems to be functioning exactly as it should.

Does anyone know if California just switched over to winter fuel blend? Is this sort of a drop even remotely reasonable, for a switch from summer to winter? I am thouroghly puzzeled!

Thanks, Gary Palmer

Compaq888 · 12-05-2006, 01:04 AM

7 mpg difference is huge. Something is not right with the car.

GasSavers_DaX · 12-05-2006, 05:05 AM

Are you DPI or MPFI? How are you calculating your FE?

GasSavers_Jack · 12-05-2006, 12:56 PM

First thing is the Gas gauge on my Honda is grossless inacurate. The first half a tank gets about 250 mile (depending on hill I am on) and the second half is luck to make 170's. I would just be carefull about your driving this next tank and take a look after that.

JanGeo · 12-05-2006, 02:29 PM

Simplest way to check is if you have a IR Heat gun - check for elevated temps in the wheels to see of brakes are dragging. Check the tail pipe - all the burnt gas comes out there if it is sooty then you are running rich. Tire pressure check every two weeks!! Check how far you can coast is a good test for something dragging - alignment, bearings, tranny and brakes.

Gary Palmer · 12-05-2006, 04:40 PM

Thanks. I don't know what's going on, yet, but when I figure it out, I'll let everyone know. My fuel gauge is similar to Jack's, in terms of function. I get the most miles out of the first 1/2 and the second 1/2 is really more like 1/3. However, the fule gauge isn't the issue. The issue is that I barely got 300 miles out of over 10 gallons of gas, which is really not very good, for this car.

The car is a DPFI. I don't belive it's running rich because I am monitoring the Oxygen sensor and it's oscilating between 0.35v and 0.8v, just like it was when I was getting 37 mpg. I'm inclined to think I have a loose connection, somewhere, or something, but whatever it is, it isn't throwing any CEL. I will probably try to check the various sensor inputs to the ecu unit, on saturday.

GasSavers_scostanz · 12-05-2006, 05:55 PM

Are you sure that the simple things are in order? Plugs, wires, cap rotor? I experienced a drop in mileage last year and couldn't figure it out for the longest time. I had just replaced the plugs, cap and rotor so I never gave them a thought. I was thinking it was the O2 sensor or a million other things. After a couple of months, I suddenly was experiencing a miss every so often and I replaced the cap/rotor with a Honda original and the miss and drop in mileage were resolved. It turned out that the cheap rotor I used was defective. The point I'm trying to make is to check the simple things first.

-- Scott