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Discussion Starter #1 (Edited)
Hello everyone,

I bought an 2002 Elantra GT 5-speed January this year (116.000 miles) and the car was in great shape, 4x new tires only 1 owner all maintenance done on dealer plus a folder with all service invoices, looking well cared.

When I get the car the performance was bad plus getting 18-19MPG, I did a lot of stuff myself and today the MPG is 22-23 and performance little better, but I still feel something is wrong with this car... its currently on 120.000 miles.

I use Torque app + ELM327 bluetooth OBD2 adapter in order to test everything, 2 issues it had/have:
1.Error code P0560 related as a bad alternator/battery; battery is new (previous owner replaced in Dec 2015), I replaced the alternator belt using correct tension and went even further passing 2 new 8awg wires for positive/ground reinforcing them, reset the code and tested everything with a multimiter, the code never came back and it seems all perfect never had any electrical issues so I consider it solved.
2.The car tilts/fail when launching in 1st gear, if I dont hit the throttle it will die, seems to be related with the canister gas valve or a intake leak; I removed the valve from the intake and tested blowing it, no air passed to the other side so the valve seems good, the gaskets in the intake are all good and I also used carb cleaner to clean the throttle body plus idle valve.. might be the other valve inside the canister itself? any hints?

About bad performance and gas mileage, here is everything I did already of course testing before changing and most of then just follows routine service as fluids/filters/belts etc, will just copy and paste as I register everything;

-new NGK platinum spark plugs PFR5N-11 (car has bad/wrong code sparkplugs..)
-oil + filter change (100% synt 5w30)
-new timing belt + tensioner + idler + water pump + new coolant
-new steering wheel and alternator belts
-had a big hole after catalytic converter that was fixed, plus new NTK O2 sensor bosch 18730055 /13461 (2nd after cat converter)
-cleaned 4 injectors using carburator cleaner + 12v battery, also replaced 8 new o-rings (don`t have a machine to equalize them.. might have a open/stuck/bad injector?)
-new clutch fluid
-new cabin airfilter
-new front rotors + pads
-transmission fluid replaced - mtf 75w85
-steering fluid replaced
-passed 2 new 8awg wires to positve and ground borns in order to reinforce the connections
-new fuel filter Beck/Arnley + new fuel Pump Delphi FE0351
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Things I am supposing after all this:
-blocked/bad exhaust outflow?
-bad ignition coil or sparkplug wires?
-open/stuck/bad injector?

Please any little help is welcome! I am getting crazy..
 

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Is it 22 city 23 highway? Or just 22-23 city? Mine got about 23 in town before the mods went on. What kind of tires are you using? When are you shifting? Since you have torque, post your long term and short term fuel trim and your AFR (air fuel ration) if you don't have those guages just make a new page and add digital display. If it was a bad injector you feel the hesitation stumbling on acceleration.
 

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Is it 22 city 23 highway? Or just 22-23 city? Mine got about 23 in town before the mods went on. What kind of tires are you using? When are you shifting? Since you have torque, post your long term and short term fuel trim and your AFR (air fuel ration) if you don't have those guages just make a new page and add digital display. If it was a bad injector you feel the hesitation stumbling on acceleration.
Thanks! I will try to log these info and post here asap, yes I forget to mention, previous owner installed 4x new tires before selling it, they are CooperMastercraft Touring LSR 195/60R15 and I am using 32psi, he also replaced the clutch kit on Aug 2015.
I drive basically every day for short periods and longer distances on highway during weekends, I can say 30% highway 70% city. But last average for example was only on highway and I drove just 280-300miles with a full tank.. I also feel the car very weak on acceleration/pulls, will try to log a 0-60 and post here too.
 

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Is it 22 city 23 highway? Or just 22-23 city? Mine got about 23 in town before the mods went on. What kind of tires are you using? When are you shifting? Since you have torque, post your long term and short term fuel trim and your AFR (air fuel ration) if you don't have those guages just make a new page and add digital display. If it was a bad injector you feel the hesitation stumbling on acceleration.
Thanks! I will try to log these info and post here asap, yes I forget to mention, previous owner installed 4x new tires before selling it, they are CooperMastercraft Touring LSR 195/60R15 and I am using 32psi, he also replaced the clutch kit on Aug 2015.
I drive basically every day for short periods and longer distances on highway during weekends, I can say 30% highway 70% city. But one average for example that was only on highway, I drove 280 with a full tank (14GL = 20MPG).. I also feel the car very weak on acceleration/pulls, will try to log a 0-60 and post here too.

*update my last average was 80% on city, and yes I do hard pulls often reaching 5.000-5.500rpm (25% of time), what I did to really check it properly was filling the tank complete then drove until gas empty light get on, then complete it again to check total fuel that was used.. I get exactly 233miles with 12.909GL = 17.92MPG...
 

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Sounds like your AFR (Air-Fuel ratio) is too rich. That explains your weak acceleration and poor fuel economy. You can view AFR on torque but if you're o2 sensor is broken/malfunctioning you might not get a correct reading. A poor o2 sensor could be causing your symptoms. They cost about $100-$150, but free-$20 at a junkyard. But if you aren't mechanically inclined you might want to consult with a mechanic for a diagnostic.
 

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I have a p0420 code in my elantra either a bad or dirty catalytic converter. Or my downstream 02 sensor can be bad. Could any of those could be giving me bad gas mileage?
 
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