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How fast should o2s switch

Old Jul 27, 2008 | 05:37 AM
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Default How fast should o2s switch

Ive been reading up on how they work and looking at what my truck is doing. I've been getting codes p0172 and p0175 right and left bank rich, I monitored my 02s with a scanner and they like to stay around 670-800mv then ocasionaly jump down to 60-100mv.

So my question is, are the o2s suposed to act this way when the engine is running rich or are they lazy and not switching fast enough and need to be replaced?

From what Ive read they should fluctuate from 200-800mv rapidly if they dont the sensor is going bad.

So if the engine was actualy running rich and the o2s where ok wouldn't the sensors read something like 300-900mv switching rapidly?
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Old Jul 27, 2008 | 09:18 AM
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They should switch rapidly. Especially cruising. They will slow down at idle, but should still switch from 200 to about 800 mv back and forth.
Make sure its in CL, and if it is, the sensors are probably going/gone bad.
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Old Jul 27, 2008 | 02:34 PM
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they switch faster than most scan tools update unless you are on a custom data screen.
the o2s could be telling you the truth though its rich. are the fuel trims pulling fuel?
have a look at the fuel pressure regulator and check fuel pressure. if you are still running an egr they can coke up a thottle body enough to cause rich codes.
is this the forced air truck in your sig? the afr is richer on those. i have never tuned a forced air engine but would not the parameters for setting the rich codes be out to lunch?
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Old Jul 27, 2008 | 09:10 PM
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Originally Posted by sreve
they switch faster than most scan tools update unless you are on a custom data screen.
the o2s could be telling you the truth though its rich. are the fuel trims pulling fuel?
have a look at the fuel pressure regulator and check fuel pressure. if you are still running an egr they can coke up a thottle body enough to cause rich codes.
is this the forced air truck in your sig? the afr is richer on those. i have never tuned a forced air engine but would not the parameters for setting the rich codes be out to lunch?
Yes the one in my sig. I have had a fuel pressure gauge on it and it didn't leak down and fuel pressure was were it was supossed to be my regulator is in the fuel tank its a returnless fuel system. No I dont have EGR but I do have an EVAP purge soleniod on the top of my intake manifold giong to pull it off and plug the hole tommarow to check that. At idle with the engine warm the STFTs are -2% jumping to -.78%
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