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Start (START)
Start enrichment is provided for under the START and START CYCLES parameters. The ECU reads the
signal from the engine temperature sensor, looks up the START value at that temperature range, and
injects extra fuel for a certain number of engine cycles after the ECU detects crank rotation. This function
is activated every time that the engine is started, no matter what the engine temperature is. However, if
there is a zero at the current temperature range, no extra fuel will be added. START values are critical for
proper starting, especially in cold climates.
At colder temperatures, the values are high, tapering off as the engine warms up. At temperatures over
100 to 140°F, most engines do not require much extra fuel so the values should be low or 0 here.
Experimentation is required for a satisfactory setup here.
It is best to not open the throttle during cranking, especially in cold temperatures. Opening the
throttle will cause a leaner mixture during cranking. The engine needs a rich mixture to start.
Tuning all the START values will take many days in very cold climates. You can usually only tune one
value per day, and you will have to wait for colder weather to adjust the colder ranges.
Systems will do 1 injection of fuel at key-on, when the Start value is greater than 0 at any temperature.
This will improve cold starting. You must have fuel pressure prior to powering up the ECU(s) in
order for this to add fuel.
Aviation systems have special software to allow manual priming without the engine turning over. You
may stroke the throttle a few times in cold conditions to open the injectors momentarily. This acts just like
a primer and may aid starting in very cold climates. Close the throttle when cranking, even if you
prime.
Start Cycles
The value entered under START CYCLES determines how many engine cycles START enrichment lasts
for. This is the number of crank revolutions times 2 on a 4 stroke engine. Some engines require start
enrichment lasting a long time, others only require a short start enrichment period. The larger the value
under START CYCLES, the longer the enrichment period. This is adjustable between 0 and 255, but a
value of 40 is probably as high as you would ever need, and do not set this below 10 because too low a
value will make the START function expire too quickly. 15-20 in 4 cylinder engines and 20-30 on 6
cylinder engines is a good beginning point.
Both START and START CYCLES must be set carefully. If the engine fires immediately at any
temperature, the START values are good. If the engine takes a lot of cranking to get running, the START
values may be too low. If the engines starts quickly but then stalls after a few seconds, there are two
possibilities; either the START CYCLES value is too low or when the start cycles have expired, the
ENGINE TEMPERATURE values are too low. Once the start injection cycles have occurred (usually 3-10
seconds), the ECU relies on ENGINE TEMPERATURE values for warmup enrichment. These two
parameters should not be confused. The START function is automatically reset after the engine stops
turning.
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