Poor Gas Mileage...causes?

[toicy4ya]

Sup guys,

I know this question might be vague but here it goes anyway... What causes poor gas mileage on a eclipse (99 spyder gs automatic )? Tire pressure is fine, rims are stock 16". There are no air leaks in the exhaust, I checked it this weekend. I recently bought the car so I cant really tell if it had or needs a tune up but I plan on giving it one in the coming months. Currently I get about 200 city miles on a full tank of gas, I know I should be getting much more than that. Any help would be greatly appreciated.


btw, i tried searching this topic but the search engine on this forum is really general.

[Turbodog97]

theres a crap load of things that can cause bad gas mileage. Bad plugs and wires, misfirings, vacuum leak(intake and etc)

Is your CEL on? Also how are you driving the car: doggin it or just regular? I would most likely go with somthin in your ignition like some new wires or a new coil pack or etc. I mean my car gets about 250-280 if I dont dog it but if I do then I could get like 100 miles and that all. Im pretty sure shifting higher gets you better gas mileage not shifting lower. Wait till it gets up to like 4 thousand and then shift.

[nova1313]

I push 280 on a full tank if I drive it well. If I drive it the fun way... I'm down around 220.

Changing my air filter helped alot, also changed my fuel filter/plugs/wires that got me a couple more mpg avg, and don't take it over 2.5 rpm :/

What gas are you using also? I use 89/91 (middle grade). When I used 87 the car ran, but the gas milage was really bad.

when I say 280 miles per tank... I'd say 1/4 of that is city driving. I spend 10 minutes to and from work each day. The rest is spent on the highway. So I can't comment on super heavy city driving.

[toicy4ya]

well I have an automatic and i keep the overdrive on. I dont dog it, just drive it pretty normally. Like I said I cant determine when was the last time it had a tune up and as soon as mybudget permits i will be giving it one. I would never think things such as wires, spark plugs and air filter would play a role in this type of problem.

[Turbodog97]

well it doesnt seem like it would be that big of a deal but the those things make a difference especially if youve never replaced them

Why keep the o/d on? Thats meant to haul things like a trailer, it doesnt give it more speed....

[96spyderman]

Uh... you use the O/D as a higher gear for highway speeds and it keeps the rpm's lower for better economy.
If your hauling a trailer with an eclipse that would look just funny as hell!!! lmao... anyways.. you wouldn't want to use the O/D if you were hauling.. you would want it off or it can be quite a burden on the tranny...kinda like trying to pedal a bike in one of the higher gears... kills your legs...good workout though... for you not the car.. he he he

[nova1313]

yah plugs and wires make a big diff I didn't think so either till I changed them. A blocked air filter can screw up the fuel/air ratio. Cause it to eat more gas I guess?

Odd off topic question but do they offer hitches for eclipses? I want to mount a bike rack on mine just to carry two bikes and I have a convertable. The trailer thing made m think of it.

But yah do a tuneup, once thats been done then go from there. See if your milage improves. Also try a different gas station. I know that sounds dumb... but I use to go to a Giant Gas Station. It's gas was cheap but it sucked. WaWa has been treating my car much better.

[spyderturbo007]

Originally Posted by nova1313

A blocked air filter can screw up the fuel/air ratio. Cause it to eat more gas I guess?

With a blocked air filter, you aren't going anywhere. Even if it is dirty you will not be using more gas, just HP. The ECU determines the air mass after the intake filter and calculates the correct amount of gas to inject, so it will not decrease your gas mileage.

To the original poster....

The most common cause of siginificantly decreased gas mileage is a shot, or really old O2 sensor. Sometimes it is accompanied by a FT CEL, but not always.

Find someone with a logger/scanner and see if it is cycling at idle and what it does at WOT. That will give you a better indication of what is happening.

[david-b]

I was going to say check the O2 sensors. If the front one is bad, this can cause terrible gas milage. Also, if you have a cat convert, a bad one could also cause the problem

[DragonofBC]

What are the readings for the O2 sensor supposed to look like at idle? WOT?

[kjewer1]

Everything but wot you should see rythmic cycling between about .2 and .8 volts. At WOT, it will vary from car to car, but somewhere in the .90s is most common.

[l_eclipse_l]

Originally Posted by toicy4ya

well I have an automatic and i keep the overdrive on. I dont dog it, just drive it pretty normally. Like I said I cant determine when was the last time it had a tune up and as soon as mybudget permits i will be giving it one. I would never think things such as wires, spark plugs and air filter would play a role in this type of problem.

All of these are essential in having the car run smoothly and efficiently.

1. Check the o2 sensor
2. Replace the air filter
3. Replace the spark plugs AND wires
4. Change the oil and filter

If you don't notice any difference in MPG after doing all of that, check the coil pack. It's a long shot, but that could have gone bad.

How many miles are on the car? That might also play a role.

Try a different gas station. I will rate those around me:

The Best:
B.P. (British Petroleum): Very good gas, found to be the best for my car.
Amoco: Also very good, I think it's the same fuel as B.P.

Satisfactory:
Mobil: Decent gas, but you can get better
Citgo: Does the job, not the best

Shit:
Kwik Trip: Don't ever buy this gas. Your car will hate you.

One other note:
When you say 200 miles on a tank, HOW MANY GALLONS ON THOSE 200 MILES? That is how you determine your MPG. Our cars tend to vary on when the little needle says to fill up, but we have a 16 gallon tank. My gas light comes on after 12 gallons, and the needle is buried. Next time you fill up, set the trip odometer and drive it normal for atleast that tank. Then when your light comes on, take it to the same place and fill up. Record the number of gallons you dump in, and divide the number of miles on the trip odometer by it. Then give us a real number.

Hope this helps you.

[toicy4ya]

I will be performing a tune up shortly However, at times I've noticed the slight smell of gas (fumes) coming from the rear of the car possibly the exhaust. Anyone ever experience this or know what this could be?

[Killa_DSM]

Have you changed your 02 yet?