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Discussion Starter #1
SO i have a 2005 Sonata 2.7L V6 GLS and I am having problems with the engine running lean on both banks. all the o2 sensors are reading normal but the fuel trim on both banks creeps up to 14.8. Someone said it would be my fuel pump or fuel filter. That's fine and dandy but I don't have 300 bucks to replace all that. I've checked for vacuum leaks and even bought a new MAF as the old one did show odd readings. The IAT *which seems like a odd spot to put it* reads around 170-187 degrees when the engine is at operating temps. the maf always reads 0.40 to 0.60 when idle and the TPS reads 4.6-5.5 when idle and will go to 86 when fully depressing the gas pedal. Car runs great for the most part considering it was bought for 500 out of a field and rebuilt top end.
 

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Being as it sat for so long you could have injector issues.
You could have a perfectly fine fuel pump and fuel filter but if the injectors are partially clogged you're not going to get the fuel the engine wants to deliver.
Obviously the ECU is not able to richen the mixture enough to compensate for the lean condition.
How does it run on the freeway or when you really put it under a load?
 

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Discussion Starter #3 (Edited)
It picks up fine. That's why I am so confused. I can go on the highway with no lag issues or hesitation and if I use the shiftronic to lock into lower gears it takes off like a bat out of ****. has no problems under load as I have pulled a stalled car with it before and it had no issues doing that. It does however have a issue when starting it from cold sometimes where the RPM's will fluctuate sporadically like it wants to stall but never does then it settles out. Right now I have no cel as I had to fix a small electrical issue and disconnected the battery. but I have went 80 something miles since then and still no CEL but my fuel trims have crept up from 0 to 12.6 on bank 2 and 7.8 on bank one. bank 2 always throws the error first then after it hits 14.8 bank one will max out at 14.8. the stft on both banks vary between -8 to +8 during idle and under load *while on the highway for example* they go up to 28 on both banks until it goes to lean mode then they will be all over the place. Maybe non related to the issue but I have a phone mount on my dash and I can see the phone shake slightly and it seems like its constant then like a big jump then back to constant while idle but I don't feel it in the car it's self and no odd vibrations from the pedals either.
 

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the stft on both banks vary between -8 to +8 during idle and under load *while on the highway for example* they go up to 28 on both banks.
I'd expect clogged injectors to cause misfire trouble codes, unless they are all clogged to the same degree (highly unlikely).
Your STFT do suggests a fuel delivery issue though, so I'd advise a fuel pressure test. Or just spend the $300 for the new pump and hope for the best.
 

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If you decided the new pump assembly no need to spend 300 on OE hyundai one. I ordered an Auto 7 402-0010 and it was the OE hyundai pump in oe box with an auto 7 label over it. It normally goes for about 150 on amazon. If you watch the price it does does dip once in a while. I picked mine up for 48 bucks. At such a low price I figured it was good to have one on hand and beats paying way more.
 

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Discussion Starter #6
Yeah I might try that. but it probably wouldn't hurt to replace the injectors either as they are quite loud.
 

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Lean on both bank,, common factor is vacuum,, MAF,, and fuel pressure,, and a Purge stuck wide open...

Scan yet,, any codes,, what is codes in Pxxxx fashion ?
 

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Discussion Starter #8
Ok hold on Ill go get them. BTW no vacuum leaks no maf issue it's brand new still have the old one they both read the exact same (check the wiring too) Could possibly fuel related in some form or fashion but I've dumped plenty of B12 Chemtool in the tank (more than I should have) multiple times and while it did help slightly on idle it still is acting like poo with these lean codes
 

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Discussion Starter #9
as stated by my scan tool P0174 System too lean (Bank 2) P0171 System too lean (Bank 1)
During idle from cold battery voltage at 13.6 V
(Need a new alternator as the voltage drops to 12.3 under load (Lights on blower motor on stereo going))

STFT B1 0.8% -anywhere between -7.6 to +8.0 LTFT B1 14.8%
STFT B2 -anywhere between -13.3 to +6.7 LTFT B2 14.8%
ECT 129F IAT 118F
MAF 0.39-4.4 (lb/min) -Same as the old one but it reads slightly lower at 0.36-0.40 (lb/min)
TPS 4.9-5.1% it will bounce sometimes do to the weather but generally stays at 5.1%
O2S B1S1 0.760 to 0.115(V) fluctuates as normal STFT B1S1 same as other reading O2S B1S2 0.410(V) ((Engine Cold) STFT B1S2 99.2%
O2S B2S1 0.800 to 0.075(V) fluctuates as normal STFT B2S1 same as other reading O2S B2S2 0.410(V) ((Engine Cold) STFT B2S2 99.2%
 

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Need a new alternator as the voltage drops to 12.3 under load (Lights on blower motor on stereo going)
That sound more like voltage drop in the wiring than an alternator issue. You might want to carry out a few simple voltage drop tests on the circuit before replacing the alternator.
 

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Discussion Starter #11
Actually already did. It is the alternator. can be proven turning my amp and and blasting tones through the sub. I have ran a 8 gauge wire from the alternator to the battery positive post and that's how I managed to get 13.6 volts before I did that it was way lower at 13.4 so not much voltage drop. And the alternator has nothing to do with my lean issues. the car had no problems for several months till it got cold last November. since then it has been this issue with running lean. I replaced the MAF sensor as everyone was saying that would more than likely fix it. wasted 130 bucks because problem was not solved.
 

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And the alternator has nothing to do with my lean issues.
Who suggested it did?

xeratais said:
wasted 130 bucks because problem was not solved.
Unfortunately, that's what happens when you replace parts based on what "everyone" is guessing could be the problem rather than having the problem properly diagnosed.
 

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Discussion Starter #13
Not saying you did. But I suppose so. Now its hunting for gremlins and I am hoping I can get it fixed soon because state inspection is due in a month.
 
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