02 Sensor stop reading after 20-30min drive time...

Ok, I've been trying to track this problem down. On the way home from LSFest my car all of a sudden developed a buck at steady cruising speed. Not a constant buck, but all of a sudden, felt like a left off the throttle real fast and blipped the throttle quick.

So I got home and logged the car. WB reading 14.3-15.1 when steady driving, 02 sensors swing between 95mv-873mv. STFT are right around +/-2% when I am driving.

Now here's the weird part... If I drive the car for more than 20 mins they all of a sudden stop reading. They flat line at 830-850 and then will randomly drop for a brief second. The STFT will all of a sudden drop to -18 / -20%. The wideband will creep down to 11.2.

Attached is a log from this morning. The first 30mins the 02's are swinging fine and the car is running great.

Around the 35min mark I rolled into the throttle to catch up to traffic and that is when things started acting up.

Around the 36min mark you can see the 02's flat line and the STFT dive down to -18 / -20%.

The car & mods:
2010 ZR1
LT headers (wrapped to help keep heat to the 02's)
No CATS
2.60 upper pulley
102 TB

I made no changes to the tune for MONTHS and went back and looked at previous logs. The 02's were swinging fine and the STFT stayed right at +/-2%. Went under to make sure no wires were rubbed through or burnt. No exhaust leaks and have been searching the forum for the past two weeks looking for any similar experiences.

Are the 02's just dead? Or am I missing something? :doh:

Update:

Took the car out again, cleaned the connectors on the 02 sensors. Looked great for the first 15mins then it started doing the same thing, trying to pull fuel, 02's get in a steady state of 830-850.

This time though it threw a CEL.

P0102 MAF Low frequency.

Cleaned the MAF with some CRC MAF cleaner. Still got the code.

Now wondering if the MAF is dying...

Update:

Negative... My Sky uses the exact same MAF. So I switched them. Car did the same thing.

Ran fine for 15mins then when rolling to a stop light, the 02s steadied out STFT tried pulling fuel.

If your wideband creeps down to 11.2, then you're running rich... which is why the narrowbands are going high and your trims are pulling fuel.

You need to find out why you're suddenly going so rich.

Quote:

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Originally Posted by 02statesman

If your wideband creeps down to 11.2, then you're running rich... which is why the narrowbands are going high and your trims are pulling fuel.

You need to find out why you're suddenly going so rich.

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Hmmm... I just don't understand why the STFT will hold then even though the WB comes back to 14.6-14.7 which is what the PCM is commanding.

Your O2's are probably bad. I had a similar problem. The STFT would max out after about 20 minutes
of driving and the wideband would be at about 10-1 even though the computer was commanding stoich

The car will do the same thing if I force it to stay in OL.

One thing I have noticed is that will usually start acting up when I leave off the gas and decal. The PCM will stay in Fuel Trim Cell 15. When the car is running normal I can leave off the throttle, decal and the Fuel Trim Cell will go from 9 (light throttle) - 15 (decal) - 9 (light throttle).

Solved:

Its the little things that bite ya.

So a buddy looked at the tune and said I def have a vacuum leak. The P0102 is a good sign of a vacuum leak somewhere.

Started going back in my mind what I did that would cause a leak or where it could be coming from.

Right before leaving LSFest, I checked my catch can to make sure it wasn't full or anything stupid.

When I screwed it on I must of not had it tight enough. Yep.. as soon as the car warmed up the can it would start to leak a little and that is when the tune would act all screwy.

Simple fix. I like those.