MartinL

About 4 weeks ago I changed my fuel filter on my 91 civic and I have noticed ever since then that my mileage has been decreasing. I used to get about 440km/33 L then it dropped to 370 /32 and just this week 315/31 .


This is quite drastic and I am trying to figure out what it is. I don't know if the filter change had anything to do with it, I do not smell any gas from the filter so it must be tight. I have oil leaking on all 4 of my plugs which I am bringing into Honda to get fixed as well as the timing belt and probably water pump. The honda mech said it could be coolant getting in through head gasket but my coolant level is high in radiator and doesn't seem to have moved in reservoir.

Any ideas? could the leaky o rings on spark plugs affect mileage that much? They have been leaking since last spark plug change and even then I got about 440km but after the fuel filter change I noticed drastic decrease.

gearbox

iTrader: (95)

is the engine misfiring? usually oil on the plugs shouldnt affect mileage.

MindBomber

Since we've had a big drop in temperature the last couple weeks I'd definitely check your tire pressure, but that couldn't be the only cause...

Is it the right fuel filter, if you used the wrong one the flow of fuel to the engine might have decreased and triggered a drop in mileage.

MartinL

It is the right fuel filter. Just strange that after filter change I noticed the drop in mileage. Don't see any breaks in the line or smell gas leaking. Two tires were off 2 psi but that was last week; all tires are at correct pressure and at same pressure when I was getting good mileage.

I'm about to go gas up right now, I put 75km on it since last fill up and see how much fuel I've used. Most driving is city...but I recall getting 350 in the city maybe even more. I usually only drive at 530 in the morning with minimal traffic and minimal stopping. I'll let you know how much fuel was used for 75 km.

Thanks

MartinL

So for 75km got it from 7.331 litres. Sounds right for city?

lazlong

For Americans that's 46.6 miles and 1.94 gallons. About 24 mpg is pretty low but not extremely low. And yes, bad injector rings can cause blowby which isn't good at all for the engine. Oil shouldn't get on the plugs, it's usually either a bad headgasket and/or head, or rings. Get it taken care of ASAP.

MindBomber

The gas stations here are also all stocking winter gas at the moment, that will hurt fuel mileage as well.

I've heard a few times of people changing a part, fuel filter is a perfect example, then having a drop in fuel mileage because the older filter was compensating for an older 02 sensor or something like that. It could just be that your engine is letting more fuel in now, but not burning it as efficiently..

MartinL

lazlong: Thank you I will get it taken care of right away. Tuesday going to Honda and setting a price.

Mindbomber: What do you mean winter gas? So if my engine is running lean in oxygen what do I do ? New sensor or a resetting of something?

MindBomber

02 sensors are rated for a certain mileage before the accuracy of the signal it sends starts to degrade and that throws off the fuel air mix in the engine, replacing that sensor is regular maintenance that always helps improve mileage. What I think what might be happening is the 02 sensor is causing the engine to run lean o2 and the older fuel filter was causing lean fuel as well, so they found a sort of balance. Now that that the fuel filter is allowing the proper amount of fuel through, the mix is being thrown off by the lean o2.

02 sensors aren't usually that expensive and the socket is only $15 at Canadian Tire, I bought one today lol.

Gas stations stock two different types of fuel depending on the time of year, the mileage you get from winter gas is much worse than summer gas.

Winter tires (if you have them), wet roads and people driving extremely slow in the snowy weather all hurt mileage too. My mileage has been down about 10% the last few weeks.

MartinL

Oh wow that is a good theory I might as well change the sensor..sounds pretty simple I think. That filter I had on was 19 years old never changed and I doubt the sensors have ever been changed as well.
Found a good article about gas blends: http://www.slate.com/id/2098672/

lazlong

This made me think of something. Have you reset the ECU? Maybe if you reset the ECU then after you've completed a drive cycle it'll get better.

edit: Changing the sensor isn't a bad idea.

MartinL

No I haven't reset the ECU. Is it simple to do? Ball point pen pushed into a little hole? Haha

lazlong

While the ignition is off, go to the fuse box and pull the ECU fuse. Give it 10-60 seconds or so before you put it back in. Or disconnect both battery cables and hold them together for a couple seconds. I forget which one it is for your gen, I haven't had mine for 18 years.

MartinL

All right I'll look it up online thanks though. gonna go pick up a oxygen sensor now I think and install later. bleh rain

"goose"Jay

they can cause the plugs to lose some spark. If you have a blown headgasket almost 99% of the time you would see white smoke from the exhaust and it would run like crap consistantly to the point where sometimes it wouldnt even be drivable. Sounds like they are trying to get $ out of you on that one. Since your an Ef i can ask this, are you dual point or multi point? dpfi systems get worse gas mileage than mpfi's do. Also you have to figure if you are dual point, you have 2 injectors and if one is clogged or malfunctioning thats a 50% fuel loss to the combustion chamber. it will run like crap. Id say start with running seafoam through the fuel system and running some through a vac line while its running to get the carbon and gunk out of it. Youd be suprised at how that will help, also if you havent already check the hoses on the evap canister if they are damaged that can affect it somewhat. Personally i bypassed mine to avoid trouble with it.

"goose"Jay

Hold the battery cables together??!?!?!?!?!?!?!?!?!
no for an obd0 system you can either pop the ecu fuse out of just disconnect the battery. obd1 and obd2 are similar except along with the ecu fuse you also remove the back up fuse. He didnt mention and MIL so why reset it?

lazlong

Well there ya go. I learned something today. Like I mentioned, it's been years since I worked on a Honda that old. lol

MartinL

It is dual point injection. I don't have any white smoke-blue smoke trailing when I drive. The only noticeable engine problem for me is the oil leaking on the plugs and quite a violent idle after the engine has warmed up. I just looked up seafoam and I am going to give it a try. Which one is the evaporation canister?

So you think I should get Honda to replace only the o rings for the oil on the plugs?

MindBomber

I'm pretty sure the o rings come in a kit with the head gasket.

"goose"Jay

replace the chamber seals theyre only like $12 for the kit might as well buy the whole valve cover gasket kit for $25. so it idles violently when it warms up or when its warming up? cold idle issues usually are fit valves warm idle issues the iacv, which can cause a major problem with gas mileage. Yea dpfi's do get crappy gas mileage in general, but if its only doing it during certain temps it sounds like a temp controlled vac line leaking somewhere. anyway you can post a video?

"goose"Jay

its all good man. Unfortunately I work on them daily 4-6th gens and i hate it. lol

MartinL

Hey goosejay I'll take a video for you and upload it here. I'll put something on the dashboard so you can hear the judder of the idle. Normally on cold start it shakes until the engine has run for about a minute (all variant on temperature). Then once the engine is at operating temperature will shake when idling (ie at red light). I'm going to clean the control valve tomorrow morning !

"goose"Jay

alright ill keep my eye out for the vid then and ill give you my opinion at that point lol.

"goose"Jay

Also i forgot to explain something to you. The evap canister is the little black can on your firewall. It will have 3 hoses coming off of it. one to the throttle body, one to a fuel return i line ( i believe its a return) and a third that goes into the firewall i do believe nonetheless its easy to find and to bypass it. When the charcoal inside them gets old they start to smell bad and can cause crappy emissions and fuel economy, and the only solution is to either replace them or bypass them. pm me if you have any questions.

MartinL

Ahh so that is the canister beside the fuel filter. Was wondering what that was. It doesn't smell odd or anything. I passed my emissions test (air care) without a problem. Been doing some reading about the IACV and it sounds like mine could be clogged. The car is quite old and quite a bit of clicks on it. Any idea where the IACV is located and how to clean it? Some sites say break penetrating fluid and let dry.

lazlong

I think (not sure) it's #18 (on the intake manifold): http://www.hondapartscheap.com/south...t=0&quantity=0

MartinL

Thanks laz, you're right. I was looking at throttle body and not intake manifold for the valve. Looks similar to IACV doing a google search.

zcostilla

I just picked up a '95 EX coupe and it gets horrible gas mileage. I switched the cap,rotor, and fuel filter today, and I noticed a faint fuel leak from the top hose. Don't know if it was there before. It's just small enough to keep the brass fitting shiny. The gas evaporates before it can pool up and drip. I'm wondering if this was my problem all along. Zac

MartinL

This past week (Sunday to present day) I have driven 280km highway and about 40km city so haven't had to fill up. I think it'll be about 370 when I do have to. Still about 70 less than normal. Timing belt, water jump, new tires, and valve seals all going on tuesday, cleaned IACV and new o2 sensor as well. we'll see.

"goose"Jay

not gonna flame ya cause your new, but plz dont thread jack =]