C5 Fuel Enrichment Problems...need help!
Thread Starter
Burning Brakes
Joined: Jun 2005
Posts: 860
Likes: 0
From: Jacksonville Florida
C5 Fuel Enrichment Problems...need help!
Alright here's the background info on the car:
1998 C5 A4
Mods: K&N FIPK, LG Streets w/ no cats, Underdrive Pulley, Ti Exhaust, and dyno tune...
Car ran fine before the LG install and dyno tune. Afterwards, got CEL and codes P-0153, P-0154, and P-1154...all relating to front O2 sensor malfunctions.
The installer had success with using the rear O2's in place of the fronts and did this with this car. The car emits so much unburnt fuel you literally get a headache when driving around town with the windows down or the top off. Exhaust tips are also showing signs of dirty/sooty exhaust buildup. Gas mileage dropped off a few miles per gallon.
Spoke with the tuner and he advised me since all the codes were front O2 related and he never used the rear-into-front setup to replace them. Bought the correct extensions and two new AC Delco O2 sensors. Installed and reset all LTFT (long term fuel trims) with Tech II. Initially LTFT's were at 0.8% and after clearing and new O2's it was at 4.7%. O2 switching showed within parameters.
Within 20 to 30 minutes two codes came back: P-0153 and P-0154. Car is back to burning fuel heavily and the unburnt fuel smell is VERY prevalent in the cabin.
Any thoughts/ideas/suggestions would be very welcome at this point. I don't want to keep throwing money/parts at the car. Any place I should look for a mechanical problem or is this all in the tune?
1998 C5 A4
Mods: K&N FIPK, LG Streets w/ no cats, Underdrive Pulley, Ti Exhaust, and dyno tune...
Car ran fine before the LG install and dyno tune. Afterwards, got CEL and codes P-0153, P-0154, and P-1154...all relating to front O2 sensor malfunctions.
The installer had success with using the rear O2's in place of the fronts and did this with this car. The car emits so much unburnt fuel you literally get a headache when driving around town with the windows down or the top off. Exhaust tips are also showing signs of dirty/sooty exhaust buildup. Gas mileage dropped off a few miles per gallon.
Spoke with the tuner and he advised me since all the codes were front O2 related and he never used the rear-into-front setup to replace them. Bought the correct extensions and two new AC Delco O2 sensors. Installed and reset all LTFT (long term fuel trims) with Tech II. Initially LTFT's were at 0.8% and after clearing and new O2's it was at 4.7%. O2 switching showed within parameters.
Within 20 to 30 minutes two codes came back: P-0153 and P-0154. Car is back to burning fuel heavily and the unburnt fuel smell is VERY prevalent in the cabin.
Any thoughts/ideas/suggestions would be very welcome at this point. I don't want to keep throwing money/parts at the car. Any place I should look for a mechanical problem or is this all in the tune?
Racer
Joined: Nov 2001
Posts: 353
Likes: 0
From: Jonesboro AR
I just installed a set of LG streets a couple of weeks ago and had this same problem. Just make sure the right side O2 is going to the right side plug and same with the left. The front O2's don't cross each other like the rear ones. You may want to disconnect the battery for a while so the ECM will relearn your LTFT's.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Sounds to me like your engine is NOT going into closed loop-and is stuck in open loop --check out with a scanner
I would make sure you didn't leave any of the grounds off
If the headers are ceramic coated on the inside--sometimes they cause problems because the ceramic coating flakes off and fouls the 02 sensors afer running it awhile
Could also be the 02's aren't heating up--Check the 02 fuse--generally marked "oxy" or "engine sens"
Check for exhaust leaks
Make sure the 02 sensor location is very close to where it was stock-For example if the stock front locations were 6" behind the bell housing seam--they should be no further away from the front than that
I would make sure you didn't leave any of the grounds off
If the headers are ceramic coated on the inside--sometimes they cause problems because the ceramic coating flakes off and fouls the 02 sensors afer running it awhile
Could also be the 02's aren't heating up--Check the 02 fuse--generally marked "oxy" or "engine sens"
Check for exhaust leaks
Make sure the 02 sensor location is very close to where it was stock-For example if the stock front locations were 6" behind the bell housing seam--they should be no further away from the front than that
Thread Starter
Burning Brakes
Joined: Jun 2005
Posts: 860
Likes: 0
From: Jacksonville Florida
Sounds to me like your engine is NOT going into closed loop-and is stuck in open loop --check out with a scanner
I would make sure you didn't leave any of the grounds off
If the headers are ceramic coated on the inside--sometimes they cause problems because the ceramic coating flakes off and fouls the 02 sensors afer running it awhile
Could also be the 02's aren't heating up--Check the 02 fuse--generally marked "oxy" or "engine sens"
Check for exhaust leaks
Make sure the 02 sensor location is very close to where it was stock-For example if the stock front locations were 6" behind the bell housing seam--they should be no further away from the front than that
I would make sure you didn't leave any of the grounds off
If the headers are ceramic coated on the inside--sometimes they cause problems because the ceramic coating flakes off and fouls the 02 sensors afer running it awhile
Could also be the 02's aren't heating up--Check the 02 fuse--generally marked "oxy" or "engine sens"
Check for exhaust leaks
Make sure the 02 sensor location is very close to where it was stock-For example if the stock front locations were 6" behind the bell housing seam--they should be no further away from the front than that
O2's are heating up as the scanner is showing no codes for a bad heater circuit and the fuses are all good. Both front O2's are routed correctly.
The original LG band clamps were used and the slip fit joints tack welded. I'll be swapping to band straps and exhaust sealant just to be 100% sure of no leaks but there is no audible leak...
Another thing that raises some questions in my mind is the car is running between 175 and 180 degrees about 90% of the time. Sitting in traffic with the A/C off it barely gets over 185 due to the new fan settings. Some have suggested it may not be reaching a high enough temperature. Any thoughts? Could this be an issue?
I have reset the codes manually in the DIC and disconnected the battery and performed an idle relearn procedure. As I drive it this week I'll know if it was of any benefit. Any other ideas or suggestions would be great...
Racer
Joined: Jul 2007
Posts: 373
Likes: 1
From: Ontario
Same Probelm !!!
I also put on that same set-up but with a LS2 intake and ported throttle body on my 99 A/4... Had a ton of codes to deal with. I finally got it down to one PO300 code engine misfire detect. It will idle okay and rev great in park .. but when you put it in gear and try to move it bogs out and floods with black smoke.. I checked all the plugs and found the right bank to be black and fouled while the left bank seemed better... Any ideas on this one.... I just also got my Diablo tuner back from getting updated can I use this to help scan out the problem? I don't want to down load a tune on it til I can get my coupe running okay 
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
You can have the engine stuck in open loop and get NO codes---I just went thru this issue on a 2001 W6--- The 02's were not oscillating as they should be when in closed loop but were hanging around .450 millivolts all the time--BUT no codes-- They should be bouncing around in closed loop between .200 to .950 millivolts--
As for the lower operating temps- You should be fine---The closed loop temp enable is set way low--On most cars it is around 92* some are at 130*----Also 2 parameters need to be met--the other is a timer--Stock settings on the timer usually is around 90-120 seconds
The tables that would affect engine operation tremendously are all in freezing type conditions --down near -40* to 32* Although 175 is rather cool is still should be OK--Also the car temp gauge is different than what the computer actually sees--You need a scanner or tuning software to read the "engine used " temp
As for the lower operating temps- You should be fine---The closed loop temp enable is set way low--On most cars it is around 92* some are at 130*----Also 2 parameters need to be met--the other is a timer--Stock settings on the timer usually is around 90-120 seconds
The tables that would affect engine operation tremendously are all in freezing type conditions --down near -40* to 32* Although 175 is rather cool is still should be OK--Also the car temp gauge is different than what the computer actually sees--You need a scanner or tuning software to read the "engine used " temp
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