JAMEPC@aol.com wrote:
[...]
: How is the PCM compensating for the rich mixture?
: negative 600 micro seconds of what?
If I had to guess (and I am) ;-) I'd say its adjusting the
fuel injector pulse width. (The amount of time each injector
stays open during the intake cycle.) Because fuel pressure
is constant, pulse width is how the computer adds and
subtracts fuel. The longer the injector stays open, the
more fuel is pumped through it, and the richer the mixture.
(And vice versa, of course.)
I don't know for sure that is what it refers to but it would
seem to be a logical assumption.
As far as what might be causing the problem, I would probably
consider two basic possibilities:
- The computer is correct and the air/fuel ratio is too rich
This is caused by too much fuel or not enough air. Not
enough air doesn't seem very likely except in an extreme
case, but its easy enough to verify by a quick visual
inspection of the air path from the inlet to the throttle
body. More likely would be too much fuel, perhaps caused
by a leaky injector(s), defective injector(s) which is/are
constantly squirting some amount of fuel even when they
are supposed to be closed, or possibly abnormally high
fuel pressure. The fuel pressure is easy to check if you
have a test port on the fuel rail. As far as leaky/gummed
up injectors go, you may want to try running a bottle of
fuel injector cleaner through the tank or pulling the
injectors for a visual inspection and cleaning.
- The computer is incorrect - it only *thinks* your air/fuel
ratio is too rich.
A defective oxygen sensor may be reading constantly rich;
if your upstream O2 sensor is over 50,000 miles old, its
probably not a bad idea to think about changing it anyway.
I'm sure I missed about a bazillion other possible causes;
everything from a weak spark resulting in incomplete combustion
to a defective PCM, but the above items came to mind as far
as the most likely explanations, and they are also fairly easy
to check.
Good luck!
---Jon-
.---- Jon Steiger ------ jon@dakota-truck.net or jon@jonsteiger.com ------. | I'm the: AOPA, DoD, EAA, NMA, NRA, SPA, USUA. Rec & UL Pilot - SEL | | 70 Cuda, 90 Dak 'vert, 92 Ram 4x4, 96 Dak, 96 Intruder 1400, 96 FireFly | `------------------------------------------ http://www.jonsteiger.com ----'
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