96 civic getting bad mileage, please help.
 

*UPDATE*
-Filled up 9.5 gallons of gas after driving 276 miles. 29 mpg
-Will mark down for the next several ones

I have a 96 Civic Cx aka EK (stick shift & no AC). Stock engine, stock everything, no mods. For some reasons I only get around 250 miles and I always end up filling up 10 gallons. Every time i filled up on gas, I reset the trip miles on the gauge so I have a measurement of the miles i get every time.
I drive normal, shifting at 2500-3500 rpm depending on the road. Rarely do I rev high. I should be getting at least 300 miles.
I just bought this car like 2-3 months ago, So I don't know when did the car started losing mpg. At first I thought it had to do with my driving style since I just learned how to drive stick when I bought the car but it's been like 2-3 months now, so I'm starting to think it's some other problem.

The CEL is not on, so I'll assume it's not a bad o2 sensor.
The car idles fine, Around 700-900 rpm when it's warm. Also, car temperature goes up to where it should be.
Things I have changed/done in attempt to fix the problem:
-fuel filter (from Autozone)
-spark plugs (honda oem)
-spark plug wires (honda oem)
-cap and rotors (honda oem)
-checked air filter several times, still pretty good. Not a lot of dirt on it.
-cleaned throttle plate (using throttle body cleaner)
-used Techron fuel injector cleaner like 3 months ago, I might use another soon
I'm about to change the pcv valve next.

One problem is that my gas pedal is stiff, hence i cleaned my throttle plate but it didn't seem to help. Could that really affect my mpg?
Or will cleaning the IACV help?

Re: 96 civic getting bad mileage, please help.
 

Start by calculating the exact gas mileage for several tanks of gas.

Does the CEL work?

Have you checked the ignition timing with a timing gun?

Re: 96 civic getting bad mileage, please help.
 

This bad mileage has been going on for like 2-3 months now, I thought the tune up would help but it didn't. So I'm quite sure that I'm only getting around 250 miles.

Is there a way to test the CEL light? I heard about stepping on the gas or something when the car is off. Please let me know

And no I haven't checked the timing yet, I also thought about that. I will check when I have the time. Will a bad timing cause a BIG decrease in mpg?

Re: 96 civic getting bad mileage, please help.
 

Oh ya, i forgot to say I just bought this car like 2-3 months ago so ya. Let me just edit that in my post

Re: 96 civic getting bad mileage, please help.
 

When you say your gas pedal is stiff, what do you mean? Is it really stiff or is it just that you find it difficult to gently rev the engine up? It might be worth it to consider taking the throttle body off and cleaning it manually and throughly, like all the little passages with a q-tip+rubbing alcohol, under the idle screw, etc. etc. The reason I ask if your gas pedal is "stiff" is because I thought I had a sticky accelerator pedal because barely touching it in neutral caused it to rev to like 1500rpm, push a little more, now at 2000rpm, etc. Turned out, the majority of the problem was attributed to a sticky IACV which became fully stuck when I parked the car for over a year and after starting it up, the idle was bouncing.

Re: 96 civic getting bad mileage, please help.
 

Your method of measuring gas "mileage" is very imprecise. The only way to do it correctly is to divide the number of miles driven by the number of gallons required to fill the tank (miles per gallon, mpg) for several tanks. Post the mpg calculations.

Turn the key from off to ON(II). Does the CEL turn on and then off after 2 seconds?

It can. Also consider that several small problems collectively are responsible for the mpg drop.

Re: 96 civic getting bad mileage, please help.
 

Your measurements, you are getting about 25 mpg. You have a stick?

To make sure you are dead on with mileage.

Fill the tank, reset the odometer. Drive to say 3/4, get gas, make sure you fill it, take the mileage off the odometer and divide by the gallons off the pump.

By the way I have an auto ex and always got about 25.6 mpgs with mixed driving, the EX's do not have the best gas mileage. The EPA revised the MPG's and the they average like 24 city and 32 HWY.

http://www.fueleconomy.gov/feg/findacar.htm

Re: 96 civic getting bad mileage, please help.
 

well I was able to get 350 miles out of a tank of gas in my ex but it seems like that has gone down to like 300 now. how does that sound?

Re: 96 civic getting bad mileage, please help.
 

I attribute it to the summer gas blend designed for lower emissions as well as the increase in Ethanol in fuel
Are you using E10 or even the dreaded/rumored E15 blend fuel?
THAT could cause some shitty gas mileage.
And as far as timing goes...my timing was retarded by a mere 2 degrees after my head swap.
2 DEGREES!
My gas mileage dropped to around 20 mpg
I then corrected the timing, moving it to about 2 degrees advanced
A 4 degree swing brought my gas mileage to about 31 city/highway mix (and I drive agressively)
So yes, timing can have a big effect on MPG
Also...if all else fails...
*puts on flame-prof suit*
Seafoam that booger, just DON'T use it in the oil.
Did it to mine just this past week, gone 159 miles on just over a third of a tank.
I shit you not, Seafoam is pretty good stuff in a pinch

Good luck!

Re: 96 civic getting bad mileage, please help.
 

Normally you just step on the gas pedal slightly to rev it up but for mine, it's kinda like harder to step on. So I have to step on it harder than usual to rev it up to the same amount. Hence i say it's "stiff", hope you understand how I described it.

And okay guys, I'll post my mileage calculation later on today. I have to get gas soon anyways. I'll see how many gallons it'll fill up to.

I'm kind of skeptical about the whole seafoam idea, but I supposed that's my last resort next to o2 sensor

And yes my car is stick

Re: 96 civic getting bad mileage, please help.
 

Don't do Seafoam.

There is a TSB for the throttle cable, look it up, but I am not sure if it affects your car, but I think 96-to some 98's.

Re: 96 civic getting bad mileage, please help.
 

Would the dealer really fix it free of charge even though my car is like a 96? I did find the stiff accelerator on the TSB list.

Re: 96 civic getting bad mileage, please help.
 

he has a CX not an EX and out of my old ex i was able to get 40+MPG babying it so dont believe what EPA ratings rate it at

Re: 96 civic getting bad mileage, please help.
 

clean your IACV with a qtip + rubbing alcohol. Try to turn manually to see if it works smoothly, listen for dirt or sand grinding inside, clean until noise free.

Re: 96 civic getting bad mileage, please help.
 

Is it better with rubbing alcohol or does brake cleaner or throttle body cleaner work too? And turn what manually?

Seems like this thread is getting a bit off track, thanks for the help with the stiff gas pedal as well but I'm more concerned about the MPG. If anyone has any advices, please drop a comment. Thanks

Re: 96 civic getting bad mileage, please help.
 

Check your fuel pressure? Fpr? Just my. 02¢ good luck man

Re: 96 civic getting bad mileage, please help.
 

I prefer rubbing alcohol because it isn't toxic to humans though it is less aggressive. Q-tip plus rubbing alcohol worked splendidly well on my car parts....I have no idea if those other stuff would work better or worse but I'd imagine q-tip+rubbing alcohol would take more time but be more thorough.

Re: 96 civic getting bad mileage, please help.
 

alright I'll keep that in mind. I can't check it right away because I'm also busy with school and work.
I'll bump this thread whenever I have updates

Re: 96 civic getting bad mileage, please help.
 

I recommend seafoam too did it to my accord mpg's went up 20 to 30 mpg's now I get about 40 mpg's a gallon Seafoam also made me notice how much carbon build up I had I now have better throttle responce better mpgs smoother idle smoother ride. The car feels lighter much much lighter before I would have to step on the gas hard to get it going at my pace now I hardly press the gas. I seafoamed my gas tank crankcase and engine.

Re: 96 civic getting bad mileage, please help.
 

I recommend cleaning the TB as well. Also- how old is your o2 sensor?

Re: 96 civic getting bad mileage, please help.
 

Do you mean cleaning the throttle plate or the whole TB?
And I'm not sure about how old it is since I just bought the car 3 months ago. My last resort would be changing the o2 since no CEL right now

Re: 96 civic getting bad mileage, please help.
 

Whole throttle body. All the passages and the throttle plate. Get a new gasket so you can remove and thoroughly clean it. Also, check the throttle linkage for binding. A sticky throttle can cause mileage problems.

Also, just so you know, o2 sensors can go bad and not throw codes.

Re: 96 civic getting bad mileage, please help.
 

Yeah forgot to mention that OP should take the throttle body off and manually actuate it to make sure that it isn't binding anywhere. If it is binding, it's likely due to carbon buildup which in that case means he needs to clean it pretty thoroughly.

True but I think we should have him do all the free stuff first before he starts throwing parts at the car. Anyway doing all of these things will make sure his car runs great regardless of whether they were the culprit or not.

Re: 96 civic getting bad mileage, please help.
 

Small Update

Just filled up 9.5 gallons of gas with 276 miles on the gauge. That mean's I did 29 mpg that last tank.

Re: 96 civic getting bad mileage, please help.
 

bad o2 sensor sometimes wont trigger a cel, nor would a failing one.