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Discussion Starter · #1 ·
Ok, I just bought a 02 hatch elantra gt and I'm starting to realize that my mpg is very low, probably around 16mpg combined, the display tells me im doing 23mpg but I knowI'm no where near that since I fill it up with around 42$ and thats gone in about 5 days. Im nt an agressive driver and my daily commute is not more than 40 miles tops. The person who had the car before me put on after market 18" rims onand I suspect thats the problem, or could it be o2 sensors or a bad cat converter, idk some one help, thanks
 

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you may start first with tuneup repairs such as replacing plugs, wires, fuel and air filter, etc... If there are too many deposits on plugs the fuel isn't burnt efficiently. Need to start somewhere and plugs would be the place to start.

Big rims shouldn't affect gas consumption too much but may throw off MPH or speedometer a little.

Good luck -and don't forget to post an update with your findings to help others
 

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Discussion Starter · #3 ·
Ok thanks for the insight, im doing what you said plus I'll just get rid of the rims since its making the ride a bit bumby
 

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Yeah, that I agree with.... and those rims usually come with low profile tires which stiffen the ride considerably IMO and so darned expensive to replace those tires. Not too mention they are much more prone to side wall rips due to potholes... not enough cushion.
 

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Discussion Starter · #5 ·
You wont belive how bumpy the car is right now, and keeping the absorber shocks in mind too since i dont want to damage them with the big rims, I'll just sell them after I take them off
 

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i'd recommend quite differently for fuel economy.

plugs, yes replace since they are cheap and wear anyhow. wires, no don't bother. test the wires for resistance and see if they need to be replaced first before you go out and waste money.

an air filter will change nothing unless its stupidly blocked, the magic of MAP sensors...

check for any error codes in the ECU, even if no check engine light is on. some do not put the light on unless received multiple times by the ECU. for example, a dying upstream o2 sensor can do this.

check for dragging brake calipers, badly worn tires, bad alignment, and check the tire pressure.

the bigger rims CAN affect FE if they weigh significantly more - higher rotational mass on the drivetrain. rotational mass has a much larger effect than stationary mass. i would hesitate to say that it would be large however...probably quite small unless weight difference is massive. it probably isn't. required torque to move wheels is also another item given the larger radius. without knowing the numbers and, hate to admit it, reviewing my physics from college its hard to say what the difference would be. in short, put that one on the back burner.

make sure oil changes are done on schedule, and if auto and it needs to be done consider flushing the trans fluid - properly! most shops don't do it properly.

worn and loose belts can effect FE. they can slip, energy is lost.

remove unnecessary weight (ie. trunk full of tools)

finally if you always go to the same gas station, try another one. worth a shot.
 

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wires, no don't bother. test the wires for resistance and see if they need to be replaced first before you go out and waste money.

I strongly disagree... yes you can check for resistance but you can't to how weak the insulation is. If old enough or dry out they can arc and then spark is weakened at the plug. May not cause a misfire but may contribute in fuel being unburned.


an air filter will change nothing unless its stupidly blocked
I disagree also only because this is a new to him car and may not have been up-kept by previous owner, cheap enough and also assures that there are no mice nests or tree debris accumulation in box area.

check for any error codes in the ECU, even if no check engine light is on. some do not put the light on unless received multiple times by the ECU. for example, a dying upstream o2 sensor can do this.
I agree here that can be a possibility and can definitely have a direct impact on gas consumption. ^ +1 Good idea to check

check for dragging brake calipers, badly worn tires, bad alignment, and check the tire pressure.
remove unnecessary weight (ie. trunk full of tools)
Also good ideas for contributing factors. Plus it helps checking some of that to get real acquainted with the new to him vehicle.
 

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I strongly disagree... yes you can check for resistance but you can't to how weak the insulation is. If old enough or dry out they can arc and then spark is weakened at the plug. May not cause a misfire but may contribute in fuel being unburned.
since all that is required of the ignition system is....ignition...generally as long as there is a reasonable spark FE is quite unaffected. once ignited, the flame wave of fuel burning takes care of itself.

insulation breakdown will usually mean degradation of the conductor - resistance increase.

but let's be realistic for a minute here and not overlook the most important part. i thought this would be obvious and implied, but maybe not so. the wires should also be visually checked for insulation breakdown or other mechanical damage. if both check out, the wires are fine.

cases of the ignition system increasing fuel consumption noticeably are usually when the wires, plugs, etc have been completely ignored for years on end. it has to get very bad to get to that point.

so in short, replace plugs for a fun time. they're cheap. inspect wires fully both resistance and visually. this is what hyundai and many other manufacturers (if not all) specify in their service manuals.

I disagree also only because this is a new to him car and may not have been up-kept by previous owner, cheap enough and also assures that there are no mice nests or tree debris accumulation in box area.
with regards to the air filter, once again i'm jumping ahead here. i would think a general check over of the vehicle would be implied, but i should not assume that.

yes, check the air filter. there is no reason not to and you'd be correct in saying there's no way of knowing if there is debris in the air box or elsewhere.

what i'm trying to say here is replacing parts just because you can is not fixing a car. its throwing darts at the problem with a blindfold on. i see a lot of dart players around here. check everything you can think of, and then when you're done check again. only then should you make decisions on what parts to buy.
 

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I had a case of poor wire that would check fine when cold, but would sputter on hot... after replacing it - all was good.

So... spending about 50 on set of wires is not a bad idea here. Sparks, wires - those are easy to replace things. And repetitively inexpensive.

I would turn my head to brakes, tires pressure, alignment.
And what most important - right foot of the OP.
 

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I strongly disagree... yes you can check for resistance but you can't to how weak the insulation is. If old enough or dry out they can arc and then spark is weakened at the plug. May not cause a misfire but may contribute in fuel being unburned.

I had a case of poor wire that would check fine when cold, but would sputter on hot... after replacing it - all was good.
@PLP......Thanks for your your perfect example. ^_^

@Zero... Not trying to argue or "win"....I was only speaking from experience. I am a mechanic by trade, so I've seen this on a variety of cars/trucks. Can't see it through inspection at times (although you can in some cases at night in near complete darkness though -can see the light show).
 

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@Zero... Not trying to argue or "win"....I was only speaking from experience. I am a mechanic by trade, so I've seen this on a variety of cars/trucks. Can't see it through inspection at times (although you can in some cases at night in near complete darkness though -can see the light show).
i'm not trying to 'win' anything here. i am speaking from experience of my own. that experience tells me that most simply throw the most common to fail parts at the car and hope they get it fixed. even trained mechanics do this - weather you do or not i have no idea and is besides the point. the point is this does not solve problems. sure you get lucky sometimes, and not others.

what i'm trying to say here - and unfortunately its being completely missed - is that anything can be tested and inspected. furthermore, it should be where practical. for example, i don't call testing a fuel filter practical due to the ease of replacement and cost of part. wires i would since the test is just about as easy as replacement.

so, testing wires. i like what you said about turning out the lights and seeing the light show. that seems like another valid test in my mind.

if the OP could confirm that the wires (or other parts) were never replaced and are wearable parts (such as plugs, brake pads, etc) then i might change my opinion. sounds like there is no way to do that with the wires. if so, you guys may be telling him to replace wires that are almost new. am i the only one that sees no sense in that??

in short i am trying to encourage the OP to do one thing: use his head. think about what he's up to before opening his wallet. not only will he save money, but he'll understand his car better and be able to make better decisions on repairs in the future.

truth is i replace wires about once in the life of the car regardless of condition. between 150-200k kms. if they're damaged before then, of course they get replaced early. but that being said i know what is going on. this is a reliability repair, not to fix a problem.

you see, my career experience has taught me this: consider everything. eliminate the impossible. test what is left to prove the fault. only then should action be taken. anytime i ignored this lesson while working on my own car i paid for it in time, money and a car that was still not fixed.
 
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