In reply to a message from sbobev sent Fri 20 Sep 2013:
OK this is what I think happens in the first 1-3mins or so in
regard to fueling. It would be easier to draw it as a flow
chart than write it out but here goes 
Sorry if it’s a bit
long and covers stuff you already know.
Irrespective of open or closed loop operation, the Fuel
Injection ECM uses the same basic multi stage process to
control injector pulse duration for any operating condition.
Primary control is established based on engine load (MAP
sensor) and engine speed (from the Ignition ECM). These
values are mapped to a 16 x 16 matrix (256 sites) that resides
in EPROM. If, as is likely the mapped value is between sites,
a two dimensional interpolation is used to calculate the
correct pulse duration.
This value is then subjected to a secondary control that
provides correction factors based on coolant temp, throttle
position and movement, engine speed and exhaust oxygen content
(closed loop only) These correction factors allow the ECM to
utilize the correct strategy for idle, after start enrichment,
warm up, acceleration enrichment, deceleration leaning and
full load enrichment.
Once the correction factors have been applied, the resulting
injector pulse duration is further corrected for battery
voltage using a programmed voltage correction strategy. (This
is necessary because the time to lift the injector pintles
increases as voltage decreases.)
The final pulse duration is then outputted and all the
injectors are triggered simultaneously.
Right, back to the first few minutes of engine run
After every engine start, air injection is enabled by the ECM
in either a cold or hot start mode. Fueling is in open loop
when air injection is enabled. Air injection also always
runs if coolant temp is below 47C. The ECM uses a strategy
based on number of injector pulses vs coolant temp to turn air
injection off. For hot starts, if the fuel rail temp is above
70C when air injection is enabled, the hot start switch
actuates a valve to purge the fuel rail (Combat vapor lock)
When the ECM disables air injection, fueling goes into closed
loop mode. The O2 sensor in the exhaust sends a feedback
voltage to the ECM which then further corrects the pulse
duration with the goal of maintaining an air/fuel ratio of
14.7:1 (Lambda = 1). Closed loop is temporarily cancelled by
the ECM if full load enrichment or deceleration fuel cut-off
is required.
When fueling is in closed loop mode, the ECM closes the purge
valves allowing vapor to flow from the charcoal canister to
the inlet manifold. The rate of flow is electrically
controlled by the ECM.
Also, as described above, the ECM performs an idle fuel trim
adaptation routine when preconditions are met. These values
are stored in RAM and are preserved provided battery power is
available. A break in power will force the trim to be reset
to factory programmed values until another adaptation cycle
takes place and then the car is driven at least 100 yards.
Cheers,
Allan–
The original message included these comments:
I’ve (reluctantly) accepted it for what it is, but I am
still trying to figure out what the ECU does 1-3 minutes
after start-up. During that period, I have some complaints.
One of the hypothesis I’ve got is that the fueling is
incorrect for some reason.
–
1994 XJS 4.0 2+2 Convertible 5 Speed Manual
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