Downloaded from www.Manualslib.com manuals search engine 7.5 CONTINUOUS FUEL FLOW RATE
The continuous fuel flow rate at a constant battery voltage
is dependent on the injector design, fuel pump and fuel
pressure used. Tests have shown that the fuel flow rate,
for the Rochester TBi system, is dependent on the applied
battery voltage.
The fuel flow rate becomes lower with reduced battery volt-
age. The ECU compensates for this effect by lengthening the
injection pulses at low battery voltages.
7.6 INJECTOR OPENING AND CLOSING TIME
The current, through the injector coil, creates a magnetic
field which moves the armature, thus opening the nozzle
allowing fuel to be injected. Short opening times therefore
require a fast build up of current in the injector. This
requires a low inductance or a high applied voltage. Short
closing times require a low holding current which is ob-
tained by reducing the opening current while the injector is
open to a current just large enough to keep the injector
open. Since the available voltage in automotive applications
is restricted to the battery voltage (6 to 13.8V) the injec-
tors are normally designed to have low inductance.
The measured characteristics of the test injector are:Inductance = 4mHResistance = 1.5 ohmStatic opening current = 1.1A *Static closing current = 0.5A ** Static opening and closing current is independent of fuelpressure.
Downloaded from www.Manualslib.com manuals search engine 7.9.5 Cold starting conditions.
Definition: Engine speed < 450 r.p.m.
During cold start conditions the low inlet manifold tempera-
tures cause considerable fuel condensation on the inner
walls of the manifold. This condition is known as wall
wetting. To ensure correct A/F ratios it is necessary to
increase the quantity of fuel injected during cold starting
conditions to counteract wall wetting. A correction factor
is applied to the base map for engine temperatures between
-40øC and 100øC.
To prevent the engine from flooding the enrichment factor is
not only engine temperature dependent, but also time depend-
ent. This is implemented by reducing the enrichment factor
over a number of crankshaft revolutions, regardless of
engine temperature. If the ignition is turned off and an
attempt is made to re-start the engine the process is re-
peated.
7.9.6 Post start and warm-up conditions.
Definition: Engine speed > 450 r.p.m.
Engine temperature < 80øC
During these conditions the engine temperature is monitored
and the A/F ratio is decreased by lengthening the base map
injection duration to ensure smooth running of the engine
and to compensate for inlet manifold wall-wetting.
