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Old 05-28-2013, 12:04 PM   #1
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Engine Codes

Check engine light came on while riding around. I noticed that the car didn't have as much oomph when i got on it. 2 codes. First one is P0420 catalyst efficiency. Seeing as i don't have Cats, i'm guessing MIL fouled out. Second one is P0174 bank 2 running rich/lean. What can i do to find out whats causing this? Also, might it be bad gas? On the way back from wisconsin, i had to fill up with 91 octane, instead of 93 which i usually put in. I added octane booster, burned off about 1/4 tank, then put in 93. I'm down to a 1/4 tank now. Think that would have something to do. With it maybe?
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Old 05-28-2013, 10:54 PM   #2
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Old 05-29-2013, 01:31 AM   #3
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Quote:
Originally Posted by PonyBoyV6 View Post
Check engine light came on while riding around. I noticed that the car didn't have as much oomph when i got on it. 2 codes. First one is P0420 catalyst efficiency. Seeing as i don't have Cats, i'm guessing MIL fouled out. Second one is P0174 bank 2 running rich/lean. What can i do to find out whats causing this? Also, might it be bad gas? On the way back from wisconsin, i had to fill up with 91 octane, instead of 93 which i usually put in. I added octane booster, burned off about 1/4 tank, then put in 93. I'm down to a 1/4 tank now. Think that would have something to do. With it maybe?
Your rear O2 sensors don't really matter , but if you don't have the MIL eliminators like a idiot like me your car is going to run rich and burn more gas than needed , which explains more gas wasted.
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Old 05-29-2013, 08:43 AM   #4
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The rear O2 sensors have nothing to do with engine control, they just monitor the catalytic converter efficiency. All that not having cats will do--without MIL eliminators or without having the rear sensors disabled in the tune--is cause the cat efficiency DTCs to be thrown. It will nor affect engine operation.

P0174 is System too Lean on bank 2 (driver's side). The causes and diagnostic tips for P0174 are the same as for P0171.

Work the list from the top down, paying particular attention to things that would only affect one bank--an exhaust leak before or near the sensor is one of the more common causes for P0171 or P0174.

Though not on the list it may also be the result of a dying front O2 sensor. As the sensors age their output voltage falls; it will still be switching but not between 0.2 and 0.85 V as it should.

The PCM sees the lower voltage as an indication of a lean mix and adjusts the short term fuel trims to add fuel, expecting that the O2 sensor will report the richer mix; however the dying sensor continues to report a lean mix (low voltage) and the PCM will once again add fuel. This will continue until the PCM has added 25% more fuel at which time it will throw a "system lean" DTC.

You can bench test an O2 sensor with a propane torch and a multimeter--here's how. You can also make your own MIL Eliminators for less than $10, $20 even if you have to buy a soldering iron...
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Old 05-29-2013, 09:08 AM   #5
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Yes, i do have MIL eliminators, that's why i figured it threw one of the codes because maybe one of them went bad. But it all of a sudden just started acting strange then the light pops on. So i don't think it would be an exhaust leak. But i will try checking out the O2 sensors.
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Old 05-29-2013, 09:17 AM   #6
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It does not take much of a leak, and the leak can be after the O2 sensor and still create a false lean condition.

Another test would be to check that bank with a wideband O2 system and see if it really is lean, if it is then there is most likely a fuel delivery problem...
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 05-30-2013, 12:26 PM   #7
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Took it to a shop to get it diagnosed. If i need help on replacing something, i'll be back to this thread. Thanks for the help guys, alot of great info.
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Old 05-30-2013, 03:24 PM   #8
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Heres the verdict or so i was told. They checked everything they could think of. Everything checked out ok. Mechanic believes the problem lies with the Diablo sport Chip that is installed in the car. Which, i've always hated that chip but i think that's a good place to start seeing as everything checked out.
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Old 07-03-2013, 08:56 PM   #9
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error code table: Diagnostic Trouble Code (DTC) Table Free Download
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Old 07-03-2013, 09:02 PM   #10
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Originally Posted by hellozaizai View Post
Forget that anyway, it's just a generic list--here are the codes from the Mustang Shop Manual...
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New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 07-07-2013, 09:52 PM   #11
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error code table: Diagnostic Trouble Code (DTC) Table Free Download
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Old 07-07-2013, 10:17 PM   #12
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SPAMMER^^^^ Mods!!!!! Really?!?!!? Go read this users posts...
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Old 07-07-2013, 10:33 PM   #13
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Wow, i figured this thread to be dead. But spamming brought it back to life. I realize i never gave an update to this situation. It was the diablo chip that messed up in the car. I had it removed and a bama tune installed. Cured the problem right up, and i'm back to zooming down side roads. No need for all the generic code reader websites.
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