At 08:01 PM 8/30/05, you wrote:
>What I'm wondering is does the throttle position sensor have
>anything to do with the initial start up when cold?
Yes. Engine start-up is an open loop mode. When the starter
is engaged, the PCM receives input from battery voltage,
crankshaft position sensor, camshaft position sensor, coolant
sensor, IAT sensor, MAP sensor AND TP sensor. Based upon
these inputs, voltage is applied to the fuel injectors with the PCM
controlling injection sequence, rate and pulse width. The PCM
provides ground for the injectors to fire in proper order and it
determines proper ignition timing according to input it receives
from the crankshaft position sensor.
>Could it be O2 sensors? I only have 63,000 KM on my truck,
>but I notice a lot of black soot out of my tailpipe lately. -Jay
O2 sensor is ignored at engine start-up because it's in open loop.
Is the black soot coming out while you're at idle or cruise?
Idle and cruising are the only two times that the pcm is in closed
loop so the O2 sensor is being used. It means that the air-fuel
mix is rich.
Engine start-up, warm-up, acceleration, de-celeration, wide-open
throttle, ignition switch to ON/OFF are all open loop modes.
O2 sensors generally have a useful life span of 60k to 80k so
it's possible that the forward O2 sensor might be the culprit
during the transition from startup to idle if you're getting
black soot out of the pipe at idle or cruising.
Another culprit could be the MAP sensor.
They're fairly expensive sensors so do some research on them
with regards to testing before just replacing them.
Bob
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