C/L WB/WOT OEM ECUs...

[Garfield Willis]

On Sat, 08 Apr 2000 18:28:45 -0700, Doug Dayson <djdayson at ix.netcom.com>
wrote:

>Is WB O2 closed loop control at WOT actually safe?
>
>I was just thinking that any fouling and/or other malfunction of the O2 sensor
>etc could result in you going way lean under load with catastrophic results...

then On Sat, 8 Apr 2000 21:50:54 -0400, "Kendall Frederick"
<fredericksk at worldnet.att.net> wrote:

>There have been a couple of stories of Fel-pro users having just that
>problem...I think I'd use the w/b to set my WOT fuel map, then run it from
>the tables most of the time.  That's what several FelPro users I know do.

Yup, in the face of additional failure modes (more electrics), you might
very well decide that O/L is a more conservative/safer approach. The
problem has often been that in an atttempt to get those O/L tables just
right, sometimes you err on the lean side, with disasterous results too.
Hence the interest in using C/L WB sensing to prevent that from
happening. That risk has to be weighted against the likelyhood of
sensor/electrics failure, for sure.

But everyone's assuming that the major role of precision O2 sensing WILL
be in the tuning/cal work that's needed for dialing in better O/L maps.
This thread is just for those intrepid souls who insist on going one
step further and pushing the envelop of C/L control. Using this sensing
technology to cheaply open that up to some who want to experiment, is
kinda like a "second-order effect". Not the main thrust of the
technology, but an interesting and alluring one.

So don't misunderstand the motivation; nobody is thinking (I hope) that
C/L WOT control is always safer than O/L. You're trading the possibility
of more *precise* mixture control, for the perhaps increased possibility
of failure in the system, especially in it's infancy. This is often the
case; I'm sure FelPro has heard from it's share of clients who blew
engines, and blamed it on the C/L controller, rightly or wrongly.

Realistically, a failsafe/fallback mode "if the WB O2 sensor suffers
sudden catastrophic failure during WOT" is probably dreaming. Where it
really matters, you likely just don't have time to decide, "oh, the O2
sensor isn't responding, let's transition to O/L". We're talkin
fractions of a second. Altho the OEM ECUs do have just that sort of
fallback, I really wonder if it's capable of responding fast enough,
should you be under *heavy* load and suffer a lean transient due to
sensor failure.

OTOH, certainly wise to consider such "what-ifs", and decide if there's
anything that can be done to mitigate. I'd say it's a sage and
appropriate observation to bring up at this point. There be some wee
dragons here. :)

Gar


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