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Old 09-13-2013, 04:51 PM   #1
Wirtz
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Default Running rich, new plugs, terrible gas mileage

I've read through all sorts of posts already and have a good idea but I need to ask. 2005 STi, stage two setup on cp internals yada yada. Catless dp, stock injectors with 142k miles and a wally 255

I just recently changed plugs, but for a good while now my exhaust has smelt really terrible and rich, especially on startup. Good amount of smoke on cold mornings until reaches temp. My thoughts are the o2 sensor up front. I just cleaned the MAF yesterday and no imporvement. Car is getting high 100s for mileage HIGHWAY when i hit 1/4 tank remaining. This is is new within the last week.


I'm guessing if the front oem o2 went bad that it would correct for this and make the car run rich and have the bad fuel economy?

Though it shouldn't matter, when I switched the plugs I went one step colder on the NGK's and my new gap is .025 as recommended. They used to be 0.02. This kind of removed a weird 2600-2900 rpm stutter when just breaching vacuum in 5th and 6th gear.

Any other likely causes? No codes were thrown. Can't remember if one of my old codes was running rich in bank 1. Something tells me yes but that was a year ago and it never occurred again.
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Old 09-13-2013, 05:25 PM   #2
BeastianSTI
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You have a wideband installed? Are you running an AP or Open source tune?
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Old 09-13-2013, 05:27 PM   #3
BeastianSTI
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Let it run for a minute at idle and get a feel for how it's running ( and if you have Open Source tune, connect RomRaider up and view the max/min on AF sensor #1. Make note of the deviation, and then turn the car off, unplug the front o2 sensor, and see if the issue gets any better. If it's the same, then do the same procedure with MAF. Report results
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Old 09-13-2013, 05:27 PM   #4
dangerousatom
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That gap is a bit small IMO for only a stage 2, if your not pushing more then 20psi its def too small. Try regaping to .028-.030, if that doesnt make a difference check the manifold grounds and all the others before buying a new sensor.

If the front O2 was actually outright bad the car would not run at all or be very intermittent/sporadic in its running and idling well.

What are you tuned on ?
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Old 09-13-2013, 05:44 PM   #5
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Quote:
Originally Posted by dangerousatom View Post
That gap is a bit small IMO for only a stage 2, if your not pushing more then 20psi its def too small. Try regaping to .028-.030, if that doesnt make a difference check the manifold grounds and all the others before buying a new sensor.

If the front O2 was actually outright bad the car would not run at all or be very intermittent/sporadic in its running and idling well.

What are you tuned on ?
Wouldn't a smaller gap cause a stronger spark? I'm not sure the impact of the step colder plugs, but... I don't think OP has enough mods to require them, either.
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Old 09-13-2013, 07:47 PM   #6
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Thanks for the response guys. As far as tuning I'm open source from P&L Motorsports by Jr himself.

I don't currently have cord or RomRaider so I can't do anything with that. Idle is fine so I guess MAF would be out of the question.

Of it helps, I have had an evap code deleted from my map not long ago but before any issues occured

I have the regular oem o2 sensor setup. So maybe I should get the AEM UEGO and call it a day?
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Old 09-13-2013, 11:20 PM   #7
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AEM UEGO will not make a difference in terms of what your dealing with....its basically just another gauge to read, you have to keep the OEM front O2 for the car to even run period.

"The short side of Spark Gap" is all about getting it right for your car and mods along with keeping it in the proper range. Making the gap bigger will increases the combustion efficiency in the piston chamber *BUT* If you make the gap too big it takes too much voltage to jump resulting in no spark, random spark, ect... When increasing the boost and fuel mix you need to decrease the gap to keep it from getting "blown out" but making it too small will take the sparks heat away resulting in inefficient combustion AKA running rich and back firing.

Wirtz at this point you dont need a step colder plug. At stage 2 i assume youat 17-18psi so a .028/.030 gap on new OEM plugs will be just fine. A good homemade grounding kit will do more then one step colder plugs at your current stage. With better grounding you can actually increase the gap because there is less current draw then from OEM ground points.
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Old 09-14-2013, 12:16 AM   #8
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Quote:
Originally Posted by dangerousatom View Post
AEM UEGO will not make a difference in terms of what your dealing with....its basically just another gauge to read, you have to keep the OEM front O2 for the car to even run period.

"The short side of Spark Gap" is all about getting it right for your car and mods along with keeping it in the proper range. Making the gap bigger will increases the combustion efficiency in the piston chamber *BUT* If you make the gap too big it takes too much voltage to jump resulting in no spark, random spark, ect... When increasing the boost and fuel mix you need to decrease the gap to keep it from getting "blown out" but making it too small will take the sparks heat away resulting in inefficient combustion AKA running rich and back firing.

Wirtz at this point you dont need a step colder plug. At stage 2 i assume youat 17-18psi so a .028/.030 gap on new OEM plugs will be just fine. A good homemade grounding kit will do more then one step colder plugs at your current stage. With better grounding you can actually increase the gap because there is less current draw then from OEM ground points.
Thanks. So .028-0.03 is the gap you would recommend on my already step colder plugs?
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Old 09-14-2013, 01:57 AM   #9
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Try regapping them and go from there. Also take note what they look like when you pull them.

Rich = all black/oily/sooted
Good and hot = white at the tip but not the whole end
Lean = all powder sugary white/yellow or even rustish tip maybe thermally bent slightly
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Old 09-14-2013, 03:17 AM   #10
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Ah okay, good information there.
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Old 09-14-2013, 11:35 AM   #11
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Thanks for the info! Guess I'm regapping my plugs to start. Maybe I'll justs get a direct oem replacement o2 sensor anyway too
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Old 09-15-2013, 07:49 PM   #12
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When it's not your plugs, check your injectors.
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Old 09-15-2013, 08:01 PM   #13
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Evap code. What was it. Maybe your purge solenoid is leaking and pulling fuel vapor or raw fuel from the tank/ canister.
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Old 09-15-2013, 11:45 PM   #14
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Quote:
Originally Posted by scoobasaurusrex View Post
When it's not your plugs, check your injectors.
Good way to check and verify this? Most of the fuel injector/pump issues I've heard of would cause a lean condition not rich

Quote:
Originally Posted by ringlander View Post
Evap code. What was it. Maybe your purge solenoid is leaking and pulling fuel vapor or raw fuel from the tank/ canister.
P0457. I have the charcoal canister completely removed from the car as the broken up charcoal was clogging the line causing issues at the gas station filling up
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Old 09-16-2013, 03:55 PM   #15
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I'm going with gap being too small as others have suggested.
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