Lean Idle Issue Sputtering

[obrut]

I have had this HP ECU on the car for about a year now without problems until today. Its a 355 SBC supercharged. Idle AFR has always been round 13.8. Today I pull the car out and it is sputtering and the AFR are lean 35:1. During initial start it idles fine for about 5 seconds then it starts sputtering and the AFRs go lean. I have checked the map, vac lines, sensor connections, etc. I have to hold the throttle for it to stay running but it is super lean.

What could be the problem:
Bad O2 sensor?
Bad EFI sensors?
Anyway to test the sensors and O2? Thanks.

[Danny Cabral]

What could be the problem: Bad O2 sensor? Bad EFI sensors?

Diagnose the following:
All sensor values correct on Data Monitor?
Failed WBO2 sensor corrupted Learn Table (unusual %)?
Exhaust leaks upstream of the WBO2 sensor?
Ignition misfire? (WBO2 sensor will read lean.)
Battery/charging system functioning properly?
Consistent fuel pressure? (Disconnect vacuum hose to measure static psi.)
Inspect wire harness/connectors for damage and ensure it's not near any high voltage components.

If you suspect a failed WBO2 sensor, and your Fuel Table is well tuned, you can disable Closed Loop (in System Parameters), and the engine should run fine until a replacement WBO2 sensor arrives. You can do this to determine if the WBO2 sensor is at fault (at least at idle), because in Open Loop mode, the ECU ignores the WBO2 sensor. So if the engine starts running good in Open Loop mode, you've found the problem. Just ensure that you don't disable Closed Loop mode while the Learn Table is corrupted from a failed WBO2 sensor. Clear the Learn Table (if the percentages are erroneous from their nominal values), or load the last "known to be good" Global Folder. Also, if the ECU detects a WBO2 failure, it will go into Open Loop mode.

http://www.youtube.com/watch?v=s3R8whD3ZWg (Interesting wideband O2 sensor diagnosis.)
http://forums.holley.com/showthread....ist-Holley-EFI (Troubleshooting Checklist - Holley EFI)

Ensure you're using the latest EFI software & ECU firmware (Link); it has "Oxygen Sensor Control Updates" (Link - HEFI_1589.eep).

[obrut]

I did the WBO2 sensor test you linked to on YouTube. It was a failed sensor. Thanks for the info!
I had a spare Bosch 7057 from my wideband in my STI. Cut and resoldered the wires and it runs like a charm.

[Danny Cabral]

Glad I could help.
I'd ensure the current WBO2 sensor location isn't causing damage by exhaust condensation thermally shocking the sensor at startup and/or during the warmup period. If you suspect it is, install a sensor bung at a better location, use a taller O2 sensor bung* or use an Innovate Motorsports HBX-1 to move the sensor probe out of the direct exhaust stream.
https://www.innovatemotorsports.com/...cat=250&page=2 (Innovate Motorsports HBX-1 Heat Sink Bung Extender)
http://forums.holley.com/showthread....ension-Harness (Read "Wideband O2 Sensor Notes")

↑ This is referring to the "wet" gases flowing through the exhaust system while the engine is cold. On most vehicles, you can literally see water spitting out of the tailpipe(s). It's imperative to prevent this water from contacting the WBO2 sensor, because it will thermally shock the heated sensor. OEM engineers go to great lengths to locate the WBO2 at its optimum location. Anyway, a poor sensor location can actually blow water directly at the sensor probe. Look at the routing direction (angle) of the exhaust pipe just ahead of the sensor. Does it "direct" the water right at the sensor or away from it?

*If using a taller O2 sensor bung, I prefer this first one:
http://www.innovatemotorsports.com/x...cat=250&page=1 (Mild Steel)
http://www.innovatemotorsports.com/x...cat=250&page=1 (Stainless Steel)
https://www.holley.com/products/exha...parts/10120FLT (Long Bung)
https://www.holley.com/products/exha...parts/10979HKR (Short Bung)
https://www.holley.com/products/exha...s/parts/534-49 (Short Bung)
http://vibrantperformance.com/catalo...1527_1533_1069 (Vibrant Performance Saddle Style WBO2 Bung)
http://www.aemelectronics.com/?q=pro...-sensor-mounts (AEM No-Weld/Clamp-On WBO2 Bungs)
https://www.holley.com/products/exha.../71014303-RHKR (Hooker BlackHeart 2¼" Clamp-On WBO2 Bung)
https://www.holley.com/products/exha.../71014302-RHKR (Hooker BlackHeart 2½" Clamp-On WBO2 Bung)
https://www.holley.com/products/exha.../71014301-RHKR (Hooker BlackHeart 3" Clamp-On WBO2 Bung)
https://www.summitracing.com/search/...sensor%20bungs (Various Angled WBO2 Bungs)
https://www.urotuning.com/products/u...=8311005184055 (UroTuning 75° Angled WBO2 Bung Adapter)
https://www.amazon.com/Degree-Oxygen...omotive&sr=1-1 (ZoomPower 90° Angled WBO2 Bung Adapter)
https://www.buildfastcar.com/product...spacer-adapter (BuildFastCar Compact 90° Angled WBO2 Bung Adapter)

Here's a few tips on welding an WBO2 sensor bung onto an exhaust pipe:
1) Buy a "tall" WBO2 sensor bung to protect against condensation damage. The WBO2 sensor probe doesn't need to protrude into the exhaust pipe I.D.
2) Before welding, thread an 18mm spark plug into the bung to prevent warping the bung and to aid in alignment & clearance verification.
3) After welding, run an 18mm spark plug thread chaser into the bung. Auto parts stores sell these double ended chasers (LINK - 14mm & 18mm).
4) Coat the WBO2 sensor threads with an anti-seize compound for rust preventative & ease of future removal.

[obrut]

I had the WBO2 originally mounted at the end of the long tube headers when I was running the FAST ECU. But it kept on giving me a WBO2 error, so I moved it back to my X-pipe on my exhaust. It now essentially reads the left and right side of the engine and the exhaust temps are lower being further back. What's weird is my STI, which makes 650 RWHP, runs the same wideband sensor about 8" off the turbo downpipe with no downsides.

[Danny Cabral]

It now essentially reads the left and right side of the engine [x-pipe] and the exhaust temps are lower being further back.

It's not recommended to locate the WBO2 sensor in the x-pipe/crossover, because the two banks of an engine measure differently.
So you could be exacerbating a potential AFR problem by trying to read both banks simultaneously. It should be in the leaner bank.

What's weird is my STI, which makes 650 RWHP, runs the same wideband sensor about 8" off the turbo downpipe with no downsides.

Sometimes, it's the WBO2 sensor's controller that's programmed much too heat sensitive.
Example: The Innovate Motorsports LC-1 is notorious for overheat error codes (usually user error).