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I<3LsENGINES
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Discussion Starter · #1 ·
Check engine light after muffler off

So I bough my g8 GT with after market exhaust on it... it is still catted due to emissions laws in Washington where I bought it from, here in Montana we have no such thing so I took the mufflers off to give it a little bit more loudness and rumble because I miss my subarus boxer rumble and a day later I had a check engine light come on. I used a diongnostics scanner and it came up with "System running too lean" and the definition of the code is FUEL TRIM SYSTEM LEAN BANK 1. Something to do with the fuel pump, fuel pump control module or the fuel pump driver module but as soon as I put the mufflers back on to see if that's whats wrong the check engine light went away... I don't understand this... I know in my Subaru when I put cattless headers, up pipe, down pipe and cattless cat back the check engine light came on due to the ecu detecting a difference in the exhaust by the O2 sensors. Did the check engine light come on due to no mufflers or is it really a fuel pump problem?
 

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I<3LsENGINES
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Discussion Starter · #2 ·
I posted this in the exhaust threads but also applies here I suppose... I took the mufflers off my 09 G8 GT for some more rumble and noise a day later the check engine light came on and the code read "system running too lean" which means FUEL TRIM SYSTEM LEAN BANK 1 and this is for the Fuel pump needing to be replaced or Fuel pump control module or the Fuel pump driver module. So I later put the mufflers back on and the check engine light went away after a few drives around.... This makes no sense to me. is my fuel pump going out? or is just because of the Exhaust?
 

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^^^^ This does not make any sense to me. If anything was wrong with the fuel pump system, it surely ought to affect both banks (not just the one). You best post the fault code associated with that definition you are stating. I see *that meaning* being assigned to a code like P0171 (bank 1 upstream HO2 sensor).
Maybe removing some of the exhaust back pressure, is fooling the sensor some. Also it would be best to know if all the normal factory installed exhaust components are still in play here. Those members that have modified their exhaust systems may have a clue as to what is going on here when altering the exhaust.
 

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I<3LsENGINES
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Discussion Starter · #4 · (Edited)
^^^^ This does not make any sense to me. If anything was wrong with the fuel pump system, it surely ought to affect both banks (not just the one). You best post the fault code associated with that definition you are stating. I see *that meaning* being assigned to a code like P0171 (bank 1 upstream HO2 sensor).
Maybe removing some of the exhaust back pressure, is fooling the sensor some. Also it would be best to know if all the normal factory installed exhaust components are still in play here. Those members that have modified their exhaust systems may have a clue as to what is going on here when altering the exhaust.
Sorry new to this... anyways the trouble code is PO171. Will having the mufflers off effect performance in a bad way? Also if it is just fooling with the sensor is there anyway I can clear that code from appearing? Im not exactly sure on what has been done to the exhaust system other than headers, x-pipe and the pipes before the mufflers the mufflers are stock. Im planning on re doing all the exhaust to a complete free flowing exhaust for best hp. But thank you no one on the exhaust forums have responded so I figured I would ask here since it was a check engine light issue.
 

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I<3LsENGINES
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Discussion Starter · #6 ·
trouble code

Ran the scanner again because the check engine light came back on and got both fuel banks 1 & 2. So im sure the fuel pump does need to replaced... when I bought the car it was on e... he put 87 octane which is the lowest you can put in these cars to top it off didn't get a full tank when leaving the dealership... so my guess is that it was ran on e to many times and or sat on e for a few months. now im stuck with the problem...
 

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^^^^ As in you feel the car is starving for fuel, and therefore a lack of power. Your posted information is lacking a lot. By your last post *are you* saying that you now have a P0171 and P0174 recorded. An that the problem is the fuel pump, because you are showing a lean condition on both banks ? You should at least prove that out by verifying that you *can not* maintain the 55 to 60 psi required whenever the engine an fuel pump are running.
If you have messed with the upper part of the engine lately, you best check to see if anything in the vacuum system has been disturbed. Any vacuum leak created in that system can lead to a LEAN condition and probably set one or more codes pertaining to that condition.
 

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I<3LsENGINES
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Discussion Starter · #9 ·
^^^^ As in you feel the car is starving for fuel, and therefore a lack of power. Your posted information is lacking a lot. By your last post *are you* saying that you now have a P0171 and P0174 recorded. An that the problem is the fuel pump, because you are showing a lean condition on both banks ? You should at least prove that out by verifying that you *can not* maintain the 55 to 60 psi required whenever the engine an fuel pump are running.
If you have messed with the upper part of the engine lately, you best check to see if anything in the vacuum system has been disturbed. Any vacuum leak created in that system can lead to a LEAN condition and probably set one or more codes pertaining to that condition.
I have not noticed any lack of power, every once in while around 5,00 RPM I noticed a loss in power which is confusing me... Yes Both the PO171 and PO174 are now both coming up when I scan for trouble codes... they will appear and go away for a couple of days and out of no where reappear... I was told by the first person who commented on this thread that if it was the fuel pump it would be affecting both the fuel banks. I don't see how I was lacking in an information when I last posted both fuel banks are now affected with both trouble codes. I have not messed with the upper part of the engine lately... no need to yet.

I only took off the axle back but placed them back on and now have both trouble codes for both the fuel banks. My plan is to go completely cattless and free flowing... I cannot stand a quite v8 super car...
 

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I<3LsENGINES
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Discussion Starter · #10 ·
Were you dumping the exhaust after the cats or were you removing the axle back system?
Just removed the crappy axle back system... For now im going to cut the mufflers out weld some piping in where the mufflers would be. I wanted to hear the car and what to expect when I swap the exhaust out for a completely free flowing exhaust kit. Here in Montana we dont have emission laws so I plan on makin her as loud as possible and idgaf about drone.
 

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At the time I made my first post, *you said* you were getting a *fuel trim system lean bank 1*, and that it had something to do with the fuel pump. I said that seemed strange, thinking that if a fuel pump was going bad, why would it only affect one bank and not both. An that it seem to relate to a HO2 sensor vs a pump. Now you say it its both banks, but when you jump on the throttle, it gets up and goes. If its a fuel pump failing, I would think there would be a large falloff in performance.
Maybe both upstream HO2 sensors are *just getting tired* and are unable to constantly cycle there MV output back to the ECM at a proper rate. I'll keep monitoring your progress however.
 

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Question 1: is the car tuned or stock tune/handheld tune?

Answer 1: get it tuned properly, an intake and free flowing exhaust will cause it to run lean. It needs to know to open the trim more... Especially at WOT.

Statement 1: research straight pipes before just chopping stuff off. No cats WILL trip the check engine light and has to be cistomly tuned out. Cutting out the mid-pipes causes a lot of crackling, and I believe you lose a little bit of torque to gain some top end hp going straight pipes... If I remember correctly.
 

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The mufflers alone should not be causing this problem. If you have a scanner monitor your O2 sensor output in realtime and look for the oscillating behavior. Look at your fuel pressure, particularly at WOT. If it falls it could be your fuel pump starting to go bad. Could it possibly be a plugged fuel filter not flowing enough for higher loads? Look at your LTFT's in the scanner as well. I'm guessing they should be maxed out based upon your code. Has any work been done to the intake / MAF? Could possibly be a vacuum leak somewhere in the engine bay causing the motor to go lean....
 

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I<3LsENGINES
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Discussion Starter · #14 ·
At the time I made my first post, *you said* you were getting a *fuel trim system lean bank 1*, and that it had something to do with the fuel pump. I said that seemed strange, thinking that if a fuel pump was going bad, why would it only affect one bank and not both. An that it seem to relate to a HO2 sensor vs a pump. Now you say it its both banks, but when you jump on the throttle, it gets up and goes. If its a fuel pump failing, I would think there would be a large falloff in performance.
Maybe both upstream HO2 sensors are *just getting tired* and are unable to constantly cycle there MV output back to the ECM at a proper rate. I'll keep monitoring your progress however.
I know I said it was only affecting the one fuel bank at first which is true... it was at first only the one... so I put the mufflers back onto the car and it stayed on for a couple more days then the check engine light went away... a couple more days later and it popped back on again so I ran the scanner and came up with both the fuel banks... I agree with on how if it was the fuel pump failing I would notice a big loss in power... but when my Subaru's fuel pump started to fail I noticed no loss in power till I hit 6,000 rpm... could this be a start in the fuel pump going out? I also agree with you on how you said it could be the HO2 sensors acting up.
 

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I<3LsENGINES
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Discussion Starter · #15 ·
Question 1: is the car tuned or stock tune/handheld tune?

Answer 1: get it tuned properly, an intake and free flowing exhaust will cause it to run lean. It needs to know to open the trim more... Especially at WOT.

Statement 1: research straight pipes before just chopping stuff off. No cats WILL trip the check engine light and has to be cistomly tuned out. Cutting out the mid-pipes causes a lot of crackling, and I believe you lose a little bit of torque to gain some top end hp going straight pipes... If I remember correctly.
The car is handheld tuned... not many other options in Montana for tunning other than that... I wish I could get it professionally tuned but no one in MT does it... looked everywhere here in MT for someone to tune my Subaru...

The car has the stock ram jet air intake and has all stock exhaust except the headers, x-pipe and mid piping which is all catted.

I already researched straight pipes but that's not what I want for this car I want it to be completely catless but same way the stock exhaust fits in... went completely catless on my 04 WRX STI and it tripped the check engine light on all I had to do is clear the codes and never came back and. I only took the mufflers off of the G8 GT to hear more rumble and a preview of what is to come... put em back on after my fun...
 

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It is your intake. let me guess, the breather tube goes ahead of the MAF.
Had the same problem with my VCM and cortex tune before I moved the tube to the MAF housing.
 

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Ah, so there is more to the car than you originally stated. Just taking the axle back mufflers off will not set any codes off. Ever. It sounds like you might have reached the limit of your handheld tune. Check for an update and if it supports full intake and exhaust upgrades, and take GT Drews' advise.

When you remove the cats you WILL trigger a code(s). You have to tune out the rear O2 sensors, which you *might* be able to do with your handheld? If you want catless, take it to a shop and tell them to replace the cats with straight pipes. Whisper it so uncle Sam doesn't hear you though.
 

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The car is handheld tuned... ....

The car has the stock ram jet air intake ......l..
Considering there was no stock 'ram jet' style intake for these cas this may be the source of your issue if not connected and tuned for properly.
 

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I<3LsENGINES
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Discussion Starter · #19 ·
Ah, so there is more to the car than you originally stated. Just taking the axle back mufflers off will not set any codes off. Ever. It sounds like you might have reached the limit of your handheld tune. Check for an update and if it supports full intake and exhaust upgrades, and take GT Drews' advise.

When you remove the cats you WILL trigger a code(s). You have to tune out the rear O2 sensors, which you *might* be able to do with your handheld? If you want catless, take it to a shop and tell them to replace the cats with straight pipes. Whisper it so uncle Sam doesn't hear you though.
I did update it and there was nothing that I could find on diablo's web site unless someone else has the the tune that they could send to me and I could upload onto it. it is the diablo trinity hand held tuner.

I know that and I can clear out codes with my handheld but didn't see anything in the options when I tuned it for exhaust or air intake...

Does anyone know of a professional tuner in the state of MONTANA?
cause I don't... I cant just get up and travel ether.
 
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