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Poor Gas Mileage...causes?


toicy4ya
06-20-2005, 01:00 PM
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
06-20-2005, 01:09 PM
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
06-20-2005, 01:09 PM
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
06-20-2005, 03:35 PM
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
06-20-2005, 04:12 PM
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

SmicAA72
06-20-2005, 05:06 PM
Why keep the o/d on? Thats meant to haul things like a trailer, it doesnt give it more speed....

96spyderman
06-20-2005, 05:19 PM
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
06-20-2005, 10:27 PM
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
06-21-2005, 07:18 AM
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. :wink: 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
06-21-2005, 03:08 PM
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
06-21-2005, 07:08 PM
What are the readings for the O2 sensor supposed to look like at idle? WOT?

kjewer1
06-21-2005, 07:10 PM
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
06-22-2005, 07:33 PM
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
08-08-2005, 08:59 AM
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
08-08-2005, 10:56 AM
Have you changed your 02 yet?

toicy4ya
08-08-2005, 02:47 PM
02?

l_eclipse_l
08-08-2005, 03:38 PM
o2 sensor

I left you a huge post before. Do all of that, and if you still don't get atleast some improvement in mileage, take it to a dealer for a diagnostic test.

toicy4ya
08-08-2005, 07:33 PM
kool, how do you properly check an 02 sensor? Any idea how much a diagnostic will go for from a dealer? Will the self diagnostic with a multimeter be the same?

Thanks again guys. I really appreciate your help.

david-b
08-08-2005, 09:43 PM
You should get a Haynes book for your car. Has how to check and replace every sensor. Well worth the money

toicy4ya
08-09-2005, 07:46 AM
You should get a Haynes book for your car. Has how to check and replace every sensor. Well worth the money

Unfortunately Haynes barely makes any reference to the 2.4 engine the GS Spyder carries. I know, I purchased it and returned it after a couple of days. Looking into possibly getting another repair manual that offers more info, possibly Chilton's. Thanks for the feedback tho.

spyderturbo007
08-09-2005, 08:00 AM
The easiest way to check the O2 sensor is with an OBD-II logger, if you can get your hands on one.

If you were local, I would let you use mine :)

Like Kevin said, you should see a consistent cycle of the voltage between 0.20V and 0.80V at idle/cruise and a steady value of 0.90 - 0.98V at WOT.

toicy4ya
08-09-2005, 08:18 AM
The easiest way to check the O2 sensor is with an OBD-II logger, if you can get your hands on one.

If you were local, I would let you use mine :)

Like Kevin said, you should see a consistent cycle of the voltage between 0.20V and 0.80V at idle/cruise and a steady value of 0.90 - 0.98V at WOT.


Thanks for your offer Spyderturbo007.

I have two questions,

1) How many O2 sensors would my car have (2.4 GS Spyder)?
2) Would a self scan with a multimeter be the same as using a OBD-II Logger? Also is that what they use at Autozone when they perform a Diagnostic scan on your car? I did one at Autozone this weekend and there were no errors, all was 100%. The guy at autozone did it twice.

BTW, for those who dont know, Autozone performs this service free of charge. Pretty Kool I think.


Thanks again guys

l_eclipse_l
08-09-2005, 10:42 AM
1) How many O2 sensors would my car have (2.4 GS Spyder)?


Your car has 2 o2 sensors. One in the header and one in the exhaust. The primary is the one in the header.

TreeFrog
08-09-2005, 02:25 PM
yeah i got the same problem, its my o2 sensor had ti checked, i'm running rich

toicy4ya
08-09-2005, 03:50 PM
yeah i got the same problem, its my o2 sensor had ti checked, i'm running rich

How did you get it checked? Which O2 sensor was it (front or rear)? Was it expensive to replace?

spyderturbo007
08-10-2005, 07:11 AM
I can only speak about the GST O2's. I do not know if the N/T's are the same. The front O2 voltage is what the ECU uses to determine fuel delivery. Low voltage = lean mixture and high voltage = rich mixture. Normally when O2's fail the voltage begins to degrade and the ECU senses a lean condition and begins to increase fuel delivery, unnecessarialy.

I just replaced my and it was $139 from the dealer, and I did the installation myself.

toicy4ya
08-10-2005, 07:32 AM
I can only speak about the GST O2's. I do not know if the N/T's are the same. The front O2 voltage is what the ECU uses to determine fuel delivery. Low voltage = lean mixture and high voltage = rich mixture. Normally when O2's fail the voltage begins to degrade and the ECU senses a lean condition and begins to increase fuel delivery, unnecessarialy.

I just replaced my and it was $139 from the dealer, and I did the installation myself.


Thanks but how do you physically check it?

Killa_DSM
08-10-2005, 07:44 AM
It sounds like you really dont know what your doing, so you should just take it to a mechanic.

toicy4ya
08-10-2005, 08:25 AM
Thanks for the discouragement but with the proper instruction I would like to at least try.

Can someone give me instructions on how to properly check an O2 Sensor? Would a self diagnostic using a multimeter be able to pick up a faulty o2 sensor? I took my car to auto zone this weekend, they performed a diagnostic scan twice and up with no errors. Would a faulty o2 sensor cause the check engine light to come on?

Thanks

spyderturbo007
08-10-2005, 11:36 AM
A faulty O2 sensor will sometimes throw a CEL, but only if the FT's become maxed out to one side or the other.

You could probably test the O2 by tapping into the O2 sensor wire before it reaches the ECU with a voltmeter, like you would if you did the "blue wire mod" on an SAFC-II.

I have never tried that and would prefer you try to find someone in your area with a logger and check it that way.

I don't think that AutoZone uses anything more than a code scanner. You need to find something that can read the entire OBD-II programing, not just the diagnostics section.

toicy4ya
08-10-2005, 12:43 PM
I see, thanks for the feedback.

geofrog
11-03-2006, 09:40 PM
Hi, I have a question about the O2 sensor, I have a 92 laser with the 1.8. I know it is far from what you guys own, but i have a 2 wire sensor, but the only ones i am able to locate via autozone, advance auto, and others is a 1 wire. any suggestions as to why.

I also am getting bad milage, about 19mpg all city and i am hoping the o2 sensor will take care of that, I have changed everything else, plugs, wire, air filter.

Thanks,
Kris

gthompson97
11-03-2006, 09:52 PM
Changed the fuel filter? And 19 mpg all city isn't that bad of gas mileage.

clipsekid99
11-04-2006, 01:25 AM
Boo bringing back a year+ old thread. Horray beer!

l_eclipse_l
11-04-2006, 01:39 AM
And 19 mpg all city isn't that bad of gas mileage.

On a 1.8L? I would expect it to be mid 20's city, if it was running properly.

kjewer1
11-05-2006, 02:30 AM
Boo bringing back a year+ old thread. Horray beer!

I would much prefer bringing back a related thread over starting a new one. The last thing we need is 5,296 threads about poor gas mileage, all of which will contain the exact same tests, parts, theories, etc. ;)


I would try the dealer for the sensor if the parts stores don't have one for your application.

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