----- Original Message -----
Sent: Tuesday, June 10, 2008 5:42 PM
Subject: Re: Repeatedly Running On A Low Tank?
Your car was running in open loop mode during the test. If the car is
not in closed loop mode, the PCM is running the engine on a stored
lookup table (the amount of fuel injected is determined by the engine
rpm, TPS reading, MAF reading). Older systems did not do a
particularly good job of "learning" parameters at idle. Still, the
air filter, unless really dirty, should not have kept the car from
passing. At idle the air flow through the filter is relatively low,
meaning the pressure drop across the filter was also low. I suppose
the combination of the lower atmospheric pressure at high altitude and
a dirty filter could have resulted in an air flow vs. sensor
relationship that was not addressed in the PCM's look-up table,
resulting in too much fuel for the air flow, causing you to fail the
test. Still, if the car was warmed up, the converter should have been
able to mask any excess fuel condition. Did it fail because of high
hydrocarbons, or high carbon monoxide readings? Was the car originally
sold with a high altitude calibration (back then cars sold in high
altitude areas often got a different set of parameters loaded to the
I did know to make sure it was good an warmed up before I got there.
IIRC, they rev'ed the engine to something like 2000 or 2500 rpm for
several seconds and held it while the testing computer sampled the
exhaust. I believe also that a second part of the test was at idle.
You're saying that at idle, it would have been open loop regardless?
I could not tell you what parameter caused it to fail.
I do not believe there was any high altitude issues with taht car, i.e.,
that there was any sort of kit or flash available for it. It certainly
ran well, even in 16k feet mountains near Denver. I do recall, it being
turbocharged and fuel injected, the amazing difference between how it
and the carbureted Chevy Citation V-6 I had at the same time ran at the
10k plus heights.
There is one other possibility that I can think of: I bought eh Sube
with 140k miles on it, and though I sold it years later with over 275k
miles on it with the original turbo unit and engine running as well or
better than it did when new, I suspect that the turbo shaft seals leaked
a little. Perhaps, with the intake fan of the turbo unit between the
air filter and the throttle body, the extra vacuum on that from a
partially restricted filter would have pulled oil thru that seal and
that that is what made it fail the test. If that were the case, I would
guess that high hydrocarbons would have been the problem.
One other factor: Coincidentally, the particular inspection station that
I used was like 3 blocks down the street from Burt Subaru - the largest
volume Subaru dealer in the U.S. at the time (turbocharged and 4-wheel
drive Subarus were very popular in Denver because they did well going up
into the mountains near Denver). Perhaps the special knowledge that the
tech had about replacing the filter to pass the test was specific to
turbocharged vehicles, or turbo-charged Subarus in particular (perhaps
they all leaked a little oil from the shaft seals at higher mileage).
But that also is pure speculation on my part.
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')
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