My Honda DD only getting 25mpg??

[AznTraitor]

K, this is my very first "honda" car and I bought it with intention of easing my wallet on gas and something that was dependable as well as fuel efficient.

it's a 97 Civic Sedan LX with a D16y7. It had a ebay catback and ebay cold air intake, I have since ditched the catback for a stock unit and I recently changed the oil, plugs, wires, cap & rotor, fuel filter, pcv valve.

In the form I bought the car I was getting 24mph on the first two tanks and then I went ahead and did everything I listed, and I am still only getting 25mpg and that's been through 3 tanks at this point. I know I only have a 11.9 gal tank, but the most I can squeeze out is 230miles before getting too empty.

I also asked this on Honda Tech, but the car will buck and surge at about 3500 rpm's on the highway which is like 75mph....the tach will drop and then bounce back up and the car is bucking and surging and if I give it a little more gas, it will clear up but it will happen at least 7-8 times on my 80mile commute.

I've also seafoamed the motor and added fuel injector cleaner...but nothing seems to help me with this crappy gas mileage and surging of the car.

any suggestions?

[DieselNuts]

lol, only 25mpg. thats funny. So far, my best is 16mpg....lol

[Wurm]

air filter, 02 sensor, MAF (if it even has one), IACV, leaky injector orings

[thepolecat]

there is so much- check the timing on it.

[Sammich]

do a tune up..

did a tune up in my maxima..went from 21-22mpg to 25mpg

[AznTraitor]

lol, only 25mpg. thats funny. So far, my best is 16mpg....lol


my jeep was only getting 14mpg!! I was spending like $190 a week to drive to work....so I know your pain....



I was told not to mess with the IACV because my idle was fine...and the surging at 3500+ rpm could not be caused by it.

I had my car scanned at Advanced Auto parts, and it had no codes, and the CEL is not on.

like I said, I already did all the basic maintence on it....plugs, wires, cap & rotor, fuel filter, pcv valve, seafoam, fuel injector cleaner

I guess I'll go back and check timing today, as for the o2 sensor....it did not throw a code....but is it possible it's bad?

[AznTraitor]

would a clogged catalytic converter cause bad mpg and loss of power and the surging?

also, I looked it up and a oem cat is like $489?! and I was told a aftermarket one will not work on my stock exhaust system?!

can someone please clue me in on this?

[uproot]

lol, only 25mpg. thats funny. So far, my best is 16mpg....lol

16mpg? wow... that is funny

[Justin.]

02 sensor does not have to throw a CEL, unless it fails....your's is prob still working, but a little on limp side, but a fresh one would render a better outcome.

[Sammich]

would a clogged catalytic converter cause bad mpg and loss of power and the surging?

also, I looked it up and a oem cat is like $489?! and I was told a aftermarket one will not work on my stock exhaust system?!

can someone please clue me in on this?

i never saw a diff..

[AznTraitor]

02 sensor does not have to throw a CEL, unless it fails....your's is prob still working, but a little on limp side, but a fresh one would render a better outcome.


soooo, should I replace both or just the upstream one?

I heard the downstream one doesn't really do much of anything?

[.blank cd]

What also gets limp are Throttle Position Sensors, which i think are on this car, check that

[B18C5-EH2]

It could be a lot of different things as many have stated, but a few stick out to me:

You could have a vacuum leak

The coil inside the distributor could be on it's way out - not enough consisent spark = crappy gas mileage and breaking up under acceleration

Possibly rotor button, plug wires, etc. I suggest only OE Honda or NGK brand plugs/wires

Deteriorated 02 sensors - do yourself a favor and order them online and ONLY get Denso or NTK direct plug-in styles - Bosch suck ass for Hondas

Valve lash adjustment could be out - have the valves adjusted

This is an "shade tree bull**** mechanic" suggestion, but also try a new fuel filter - get one from the Honda dealership

Check your tire pressure - "what?" - yes I'm serious. Tire pressures can actually affect mpg

Believe it or not this is one of THE hardest things to properly diagnose and repair the first time. Since you have no check engine codes being stored it makes it much more difficult. I have a feeling hatever is causing your hesitation on the highway will throw a check engine light soon - hopefull for you it'll be really soon. That will be the biggest step towards better mpg IMO.

If it's a spark break down then you can see how that would cause bad mpg and stumbling, right?

Good luck! Keep us updated!

[Bpeterson]

hey does your gas light work b/c i thought the same thing in my 97 civic with a y8 but the gas light ended up not working and i hit the empty line at about 230-250 and i can still go to at least 310 - 320 just wait until you hit the end of your gas gauge fill a gas tank up and ride till it dies

[AznTraitor]

okay, so I replaced the o2 sensor today and it still bucks and surges....


but now, once the car is warm, from a stand still the car will bog heavily at take off??!

I'm at a loss on what it could be, as I've done the tune up, replaced fuel filter, seafoamed, and now o2 sensor!

[Sammich]

try to rereplace your plug wires

[seanrg1116]

you need to do a leak down test

[Justin.]

If you replace one, replace both.

[Zeeb]

in my s200 i average 23 mpg