Re: Check engine lights on

[Chris Newbold <newbold@telerama.com>]

Neil Swanson wrote:

> We get many calls everyday about "my light came on, when can I come in".
> Some are as simple as the gas cap is loose or missing.  Many bring up O2
> sensor codes and get a new sensor or 4!.  Many more bring up "random
> misfires" as the 1551 will say.

I think these are the side-effects of the fiendish OBD-II requirements
to detect every possible "problem". The trouble is, most of the things
which must be detected cannot be sampled directly, or are not unexpected
during normal operation.

Take misfiring. It cannot be measured directly, so it's inferred from
O2 sensor and timing data. If a bast of unburnt mixture is detected when
cylinder X would be exhausting, that's "misfire". Seems like that's
likely to happen during a cold, start too...

I think the software guys are walking an exceedingly thin tight rope
between many false alarms, which annoy customers, and failing OBD-II
certification because they don't catch "real" problems.

FWIW, my 12v 90 stumbles a tad on start up if it's been sitting for
several days, but nothing I'd consider abnormal. Doesn't happen at all
when it's really cold, though (single digits, F). Never seen a check
light except for when my O2 sensors went south. But, I don't even
have OBD-I :-)

-Chris
1993 90CS 5spd 72k miles