[Diy_efi] Need help from the experts diagnosing lean state upon

[Adam Wade]

--- ralph granchelli <rgranchelli at yahoo.com> wrote:

> The problem I am having is as follows. Sometimes
> when I start the engine either hot or cold it will
> go into a real lean state, around 22:1.It will stay
> this way until I restart.

Well, since you confirmed that it is reading from the
same load/speed map site either way, we can conclude
that the engine speed and engine load sensors (TPS,
MAF, MAP, whatever combination you are using) are
delivering correct readings, and the ECU is
interpreting them correctly.  And you have it
programmed not to go into closed-loop mode, so it's
nothing to do with the O2 sensor.  What does that
leave?

I don't know about your particular unit, but it used
to be standard practice for many automotive and some
motorcycle ECUs to check ambient air temp and density
at startup, and not again until the next key-on. 
Often this was done so that a pressure transducer
could be eliminated; for instance, the MAP sensor
could be used prior to cranking the motor.  If your
setup reads like this, it could be getting a bad
signal from a pressure or temperature transducer (bad
harness, connector/connection, or sensor).

Another possibility is that one of the temp sensors
(ambient/intake or coolant) is situated somewhere
where it receives undue amounts of heat when parked
hot; perhaps the CTS is in a pocket on a head where
the coolant locally gets extremely hot when the water
pump is not turning, or (more likely) the ambient
sensor gets heat-soaked, perhaps from a hot exhaust or
something.  Especially with the AAT sensor, reading
more than 150 deg. F would tend to make the ECU think
that air density was much, much lower than it actually
was, and to deliver a very lean mixture accordingly,
using the multiplier table for air density.

Note that I'm not familiar with the system under
discussion, and am offering general comments about
possible culprits.  This may well be a "known issue"
with the unit itself, and my comments may not be
applicable.  They're meant as general brainstorming
for troubleshooting the symptoms.  Hopefully someone
who knows your specific system can chime in about
anything particular to the unit that might be helpful.

=====
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| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |
| M/C Fuel Inj. Hndbk. @ Amazon.com -  http://tinyurl.com/6o3ze |

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