I did a lot of probing of this system over a few weeks a few years ago
on my 91 Civic LX, trying to get it to pass emissions. honda-tech.com
turns up no typical solutions (really no solutions, period). This
thread has the best treatment I have seen so far and is consistent
with my troubleshooting:
'91s do not fail on account of EVAP.
If you really want to make sure of that, stuff a ball-bearing into the
purge line so nothing can get into the intake.
Code 92 is the same as P0441. Chances are excellent that the Purge Control
Valve is corroded.
This went unsolved--it never passed. But one of my theories was that a
hose in the evap system to the throttle had failed, hence causing a
vacuum leak, hence causing the computer to misread, hence causing poor
MPG was still good, however.
I do not have the 91 Civic anymore. I sold it to a family who lived
outside the area that requires emission testings.
had the same problem on mine last time around - it turned out that the
injector o-rings had failed and gas was dumping past them straight into
the throttle body. the ecu could compensate at freeway speed by
reducing injector pulse width using the O₂ sensor feedback circuit, but
at low speeds, i.e. smog check speeds, leakage was too great.
modern gasoline formulations had turned the o-rings into black noxious
goo rather like a bad gummy bear. replaced with "viton exp" and don't
expect any more problems - passed emissions like a champ.
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