headrec*

Hey

In the past with cars I've always just bought parts I thought needed to be replaced when my cars were getting bad gas mileage. This time I'm hoping to diagnose it before spending the cash.

The car is a 98 Civic ex. I do about 85% highway and 15% city and I am averaging 28-30mpg. Not that this is terrible I just feel like a civic should do better. My eg hatch did about 38-42 mpg all the time city or highway.

Anyway are there some things I can do to generally look over the car?

Some things I have tried:
Checked plugs (seemed fine)
Checked air filter (almost new)
Checked distributor cap/rotor (seemed fine)
Checked tire pressure as well as other small things
Fuel injector cleaner (yeah this probably doesn't do anything but yeah...)
Car has great compression and runs great with no check engine lights

Some things I have yet to check:
Spark plug wires (they look old but is there a test I can do?)
O2 sensor (is there a way to test this?)
Ignition timing (don't have a timing light but car appears unmolested)
EGR valve (is there a way to test this?)

Any other suggestions or input would be greatly appreciated.

Former User

Do you have a manual or auto transmission?

How old are the plugs, wires, cap, and rotor? The resistance of the plug wires must be less than 25k Ohms. You can probably get a free rental for an inductive timing light at an auto parts store.

Does the CEL work?

What is the temp needle reading when the engine is fully warm and how long does it take to get there?

What is your driving style?

headrec*

Manual transmission sorry forgot to include that.

I just bought this car so I don't know the history on it. The plug, cap, and rotor all looked ok. The plug wires looked older. I'll grab my meter and measure the resistance in those tonight.

CEL works just had safety and emissions done on it today.

The needle gets to about 3/8ths of the way up the gauge. You can barely see the temperature symbol under the bottom of the needle. It takes a couple of minutes of driving for it to warm up. Its slowish compared to other cars but all the hondas I've driven seem to be like this. I think its due to the small motor size.

My driving style is pretty varied. I drove the car really nice after the first tank because I was wanting to see if my driving style was causing the poor gas mileage but it didn't change. I've had about 5 tanks through it now and they all fall in the 28-30mpg range.

Former User

Given that you just purchased the car, my recommendation would be that you replace the plugs (NGK only), wires, cap, and rotor and then adjust the ignition timing to spec. Then go from there.

headrec*

Ah, the typical throw parts at it til it works approach. Epic.

Former User

Are you familiar with the fundamentals of automotive maintenance (ignition system tune up)?

tlarimer

iTrader: (3)

What brand of fuel are you using? What octane rated fuel are you using? Seeing that you are in UT, you should already know, but if not, all of our 87 and 89 rated fuels are a 10% ethanol blend, which I have found to drastically affect fuel consumption.

On my 1999 Civic LX D16Y7, if I fill up with 87 or 89 blend I get 28-33MPG, but if I use 89-91 non-ethanol blend my mileage jumps up to 38-41MPG. It takes a while to find fuel stations in our area that dont use ethanol blend. Read the pumps, it clearly states whether or not that station uses blended fuels.

Aside from that, not knowing the history of the car, it's pretty safe and fairly inexpensive to replace most common tuneup items from your local Honda dealer. I think I spent right around $100-120 for ignition tuneup items from Honda this past February. And overall it was worth every penny, better starts, smoother idle and a slight increase in MPG.

headrec*

Yes I am familiar with a tune up. I was just hoping to avoid spending 100+ on something I 'think' to be the problem. I want to know what the problem is before spending the money.

And that is true I remember going on road trips before we had ethanol in our gas and going to states that had the 10% in the gas and it made quite a bit of a difference. I'll try looking around for a pump without ethanol but it does seem like all of the stations are that way. Maybe I'll try filling up with premium and see if that helps.

I wouldn't hesitate to spend the money on tune up items but I've already spent more on this car then I was planning and I'm just trying to keep it cheap at this point.

tlarimer

iTrader: (3)

Try looking at Chevron, that's the only stations up here that don't have 89 blend. But maverick, kum n go, etc. all have ethanol blends.

Not saying that 91 octane is the answer, but it's the only fuel available in our region that does not have ethanol. I use maverick and these are the mileages with different fuels,
87-ethanol blend 25-28mpg
89-ethanol blend 28-33mpg
91 no blend 38-41mpg
Not sure if elevation plays a role in any of that, but these are hard numbers run on the same vehicle over the course of 6 weeks.

Try running a couple tanks of non-ethanol blended fuel and see if your mileage changes.

slogfilet

iTrader: (1)

It may be hard to compare mileage to your EG hatch... which model did you have? There were some pretty light cars in that gen, with the VX and CX having some pretty tall gears (and the VX being purpose-built for mpgs.)

Definitely try to source some unblended (non-ethanol) gas. I think E0 contains about 3.4% more BTUs than E10, but your tune can make a huge difference in how your engine handles ethanol.

You can search for unblended gas here.

Honestly, the biggest thing you can do to improve your mileage is keep your foot out of it as much as possible. Sounds lame, but it really is true.

tlarimer

iTrader: (3)

We are comparing 98 civic ex to 99 civic lx. Granted we are comparing D16y8 to D16y7, but I think i remember my 98 civic ex sedan getting closer to 35-37mpg.

My b16a powered EH3 gets 34 consistantly.

slogfilet

iTrader: (1)

Sorry for the confusion, I was referring to the headrec's eg. I'll try to quote better.

headrec*

My eg was a dx. It had a d15b with a non vtec head. I drove the **** out of that thing compared to this. That car seemed really gutless. My ex seems a lot stronger. Maybe its the vtec haha.

Like I said I will try the gas thing for experimental purposes.

Does anyone know how to diagnose the O2 sensor or the EGR? Just want to check everything out I can for free first.

Former User

A 98 Civic EX does not have an EGR system.