Re: 1998 O2 sensor

[garwillis@msn.com (Garfield Willis)]

On Tue, 6 Jun 2000 13:50:27 -0500, "lpwcruzr" <lpwcruzr@netzero.net>
wrote:

>If I understand right, the 98 GM trucks had 4 O2 sensors. 2 of them mount
>after the separate catalytic converters. I am looking at installing a 98
>Vortec 350 into a truck that has a single cat. Will it throw anything off to
>have both of the 98 O2 sensors mounted in the same exhaust tube after the
>single cat?

In this case, I doubt it very much. You're very likely gonna be just
fine. Reason being, what the ECU is looking for in the post-cat sensors
is any large correlation between O2 swings in the pre-cat and the
post-cat. Nuther words, it's *expecting* to see very little signal swing
in the post-cat. The error condition is when it DOES see significant
swings. So in a nutshell, the front one MUST swing around, and the aft
one had better NOT much.

These conventional sensors aren't fast enough to see much of the
cylinder or bank-specific O2 pulstations, so there isn't any attempt to
match up pre & post signals in time; it's just looking for proof that
the cat if effective, by lookings for NO major O2 excursions in post-cat
exhaust, during closed loop. The reason why they have two post-cat
sensors is to satisfy the requirement that with multiple-cat installs,
the diags can flag *which* one is misbehaving/wornout.

BTW, I think you're wise to be planning mounting them both back there on
the one pipe; that'll preclude problems that might occur if you
attempted to use just ONE sensor to feed both post-cat O2 inputs. I've
heard that in some cases this doesn't work, due to how the ECU circuitry
that reads the sensors is designed. You could TRY using just one, and it
might be able to drive both inputs and keep the ECU diags happy, but be
prepared to revert to using them both, if not.

HTH,
Gar


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