Where is oxygen sensor?

[pangea]

Hi all,

I have 02 elantra gls with odometer 130K+

Recently, I've been getting very poor MPG after I changed spark plugs (bosch 2+ platinum to autolite platinum). I used to get 400+ mpt but now it barely makes 350+ mpt. 85% of my driving is on highway. So the saga began.

changed spark plugs to champion platinum - no improvement
changed spark wires from stock - no improvement
changed PCV valve from stock - no improvement

Those anyway had to be replaced for maintenance, so no regret.

My last trial is going to be oxygen sensors. I bought my elantra at 55K, so I think they need to be replaced too. I already ordered two (NTK brand, don't know if they are any better or worse than OEM). Though I have an oem repair manual, I can't find one at which it should be in the diagram.

Is the one in the circle O2 sensor? As far as I know there are two sensors but I don't know where the other one is. I'm newbie mechanic. Could you guys help me?

And is there anything that I should be careful when I replace them? I ordered sensors without oem connector, just 4 wires ones, so I don't know if I can correctly connect them. If there is still no improvement with O2 sensor change, I'm going to mechanics.

[Pete03GLS]

uh... i think the one u circled is one of them, and i think the 2nd one is some where along the exhaust piping? after the cat maybe? im not sure tho bcuz ive never looked at my own exhaust. but i think the 2nd is some where further down the line.

[pangea]

Thanks, Pete for prompt answer. I will look for an after-cat-one this weekend. Your car looks awesome!

[Pete03GLS]

no problem. the car in my sig isnt mine, altho, my car is the same thing, minus the body kit, and rims.

this, is my car:
http://i3.photobucket.com/albums/y74/ricochetx16/car%20stuff/thirdtry.png

[pangea]

:)
I have silver too. Mine is the same thing as yours, minus rims. I still have stock steel wheels. :s

[Pete03GLS]

u have a drop? :D

[Matrixloader]

the mileage your getting is about the average MPG everyone here gets. I normally get over 400mpt when driving on long trips on the highway.
i do mostly street driving so the my average mpt is around 310-350

changing your 02s just to improve MPG when they are still working fine might not help much. also oxygen sensors can be very expensive, other elements also come into play when trying to improve MPG, like having nice clean oil, I always seen better results with Synthetic oil so i use that in all my cars. keep your tires properly inflated.
most tires max pressure are 44psi, running 40psi helps a bit more than 30-35psi.

make sure you have a clean air filter, a dirty air filter will rob you of power and MPG,
If you have a stock intake, Buy a K&N air filter for your stock air box, you will see better results.

it also depends on your driving style, if you drive like you just stole that car then your MPG will drop, if you drive like a senior citizen then your mpg will improve.

[pangea]

Thanks for your input matrixloader. When I purchased my elantra with 55K, I was quite surprised to get 400+ mpg. And it never let me down until 125K. Constant 400+ mpg. I drive 75-80 miles on highway. I don't drive crazy, but I'm not a senior citizen driver either. Right, it might be an age of my elantra. Expecting high MPG on 130K machine might be too optimistic. But MPT can't drop almost 50 miles over a single trip to the gas station. Constant 350 MPT thereafter. I bought a pair of NTK O2 sensors from ebay for around $50. NTK (NGK) makes no crap, so I thought it's worth a shot.

My filter is clean, tire pressures are 32 psi (I don't like to go over 35psi cause I live in sunny CA. Last summenr, I teared side walls of both of my 1 year old front tires with overpressure). I just like to keep fixing and moding something on my cars. :)

BTW I'm planning to install SRI kit. I hope it helps my highway MPG. If it doesn't, will go back to stock.

[Matrixloader]

don't buy a SRI because it will just suck in hot air from your engine bay, buy a Cold air intake instead.
A Cold air intake sucks colder air and will not lower you MPG, only improve it.

the 01-03 elantra does not have a MAF, so the best intake in my opinion would be the 2003 4cyl tiburon intake because that engine is the same as the 01-03 elantra.
ebay has the aem Cold air intake for cheap, and AEM is street legal in california.
http://cgi.ebay.com/ebaymotors/AEM-COLD-AIR-INTAKE-2003-04-HYUNDAI-TIBURON-4CYL-21-522_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247 QQcategoryZ38634QQihZ019QQitemZ290146247664QQrdZ1Q QsspagenameZWD1V
http://cgi.ebay.com/ebaymotors/AEM-Cold-Air-Intake-Hyundai-Tiburon-2003-03-2-0L-4-cyl_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247 QQcategoryZ38634QQihZ013QQitemZ230230931533QQrdZ1Q QsspagenameZWD1V
http://cgi.ebay.com/ebaymotors/AEM-COLD-AIR-INTAKE-2003-HYUNDAI-TIBURON-2-0_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247QQ categoryZ38634QQihZ010QQitemZ200222223214QQrdZ1QQs spagenameZWD1V

[pangea]

Will try CAI instead. Thanks for the link too Matrixloader. This site rocks!
Just one thing that worries me about CAI is hydro soak. There are two roads where I travel often and get flooded when it rains. It's a puddle mostly, but heavy rain makes it small river. The one I went through last winter fried one of my fog lights. I may have to just stick to the stock. :s

[steev-o]

as long as you can stay out of water that comes higher then your intake you will be fine. Another solution is a splash guard against heavy rain.

The evry best thing to do against rain is to mount the intake between the battery and the fender on the inside. Just shift your battery over towards to middle, and have the intake sit in the corner behind your right headlight. This will allow colder air then a SRI, but avoids water in your intake.


EDIT:

another thing that will help, like matrix mentioned, is to replace the stock air filter with a KN one. You can get them at any o'reilly's for +/- 35 bucks. It improved my MPG and i had some more power as well.

[pangea]

Thanks for the all the inputs.

I located after-cat O2 sensor. It was located along the exhaust pipe near oil pan. Now the challenge is to take the old one out and installing the new one. I'm just writing this up to help other people who are going to go through the same trouble.

You need 12mm socket or wrench for header cover removal and 22mm for O2 sensor removal (preferrably combination wrench, for socket type you need a deep, very deep one). There's plenty of room to work with after-cat O2 sensor, but not for the one on the header. I first sprayed lubricating sprays to loosen it up and cut the wire. If you need to save the connector to use universal type, leave some length of wires on the connector side. Then put the wrench on the sensor and wack it with rubber mallet until it starts to turn. It's freaking hard to take it off with muscle only. Once it's loose, just screw it out. Save it just in case new one doesn't work.

Now time for wiring universal sensor. I bought NTK O2 sensor since the wire colors are same as OEM sensor, but the stupid ebay seller sent me Denso ones. Following is the wire colors scheme. If you decided to go with universal one like me, make sure you buy 4-wire type.

Function OEM NTK DENSO
Singal + Black Black Blue
Ground Grey Grey White
Heater White White Black
Heater White White Black
(no polarity for heater wires)

Connect wires from new O2 sensor to the saved connector and put some heat shrink tubes on.

Put some "high temp" anti-seize on the threads and put the new one in. The tightening torque specified by Hyundai is 50-60 Nm (37-44 lb-ft). That's the amount of the torque that is little less than the torque you apply on wheel nuts.

Reset ECU and drive. If you don't see CEL, you are pretty much good to go. I hope this helps.

P.S. I decided to go with both CAI and SRI setup. CAI for summer and SRI for winter. :) Here in Northern CA, winter is rainy season. Thanks for the recommendation guys.