6.3 Tuning fuel 6 TUNING THE MS3PRO
A wideband O
2
sensor is immensely helpful here, but don’t get too caught up in seeing perfect AFR numbers
through the whole transient event. Adjust it until it feels right, snappy and responsive with no hesitation. The feel
is more important than looking for perfect numbers. If you want perfect numbers, you may want to try the model
based acceleration enrichment. Setup basic AE first as described here. Next you’ll adjust the other set points
you’ve setup for faster throttle rate changes. Repeat the process for the medium speed tip in, then the mid-fast,
then the fast.
6.3.6 Startup / warmup fueling
On the first couple starts, you’ll want to use whatever combination of fuel and throttle can nurse the engine along
until it is warmed up, and dial in the fuel at idle while hot. The reason is that this setting can affect startup behavior,
and you will want to have good, solid values in the VE table (at least at idle) before you can get final values for the
startup sequence. Here is the sequence that MS3Pro fueling goes through while starting.
1. When the key is on, the MS3Pro will turn the fuel pump on for 2 seconds and fire one priming pulse to clear
air for the lines. (You can disable this feature by setting the priming pulse to zero.)
2. When the engine starts turning, the MS3Pro will run off the cranking pulse width table in batch fire mode until
the RPM rises above the cranking RPM threshold.
3. Once the RPM rises above the cranking threshold, the MS3Pro transitions to the main fuel table. It will initially
multiply the pulse width from this table by the warmup enrichment (WUE) and afterstart enrichment (ASE)
combined.
4. The ASE tapers off based on a user defined curve. After the ASE tapers away, the MS3Pro will run on the
main fuel table multiplied by WUE.
5. When the engine reaches normal operating temperature, as defined by the WUE curve, the engine will run
on the main fuel table, and the warmup cycle is over.
Now, let’s have a look at the menus in more detail.
6.3.6.1 Cranking / Startup settings
• Cranking RPM: This is the RPM where the MS3Pro uses cranking pulse width. You want this to be high
enough that the engine does not exceed this if turning at its “cranking, but doesn’t catch” speed, but less
than the speed it will settle into as soon as the engine has started.
• Flood clear TPS: When the throttle is open above this percentage below cranking RPM, the MS3Pro will
conclude you are trying to clear a flooded engine, and turn off the cranking pulse width.
• Cranking fuel pulse rate: The injectors are batch fired during cranking. This parameter lets you inject fuel
every ignition event or every other ignition event at double the cranking pulse width number. Usually you
would only use the “Alternate events” setting on engines with more than eight cylinders.
• Priming pulse delay: This allows the MS3Pro to wait a number of seconds after key on to fire a priming pulse.
• Ignore MAT correction during ASE: This can be used to compensate for MAT sensors that absorb heat from
the engine. Turning this on will cause the air temperature correction to reset to 100% until the ASE taper is
over.
• ASE count units: You can specify the length of the after-start enrichment in engine cycles (every other crank
revolution for a four stroke) or tenths of a second.
Most of these use a tuning curve that specifies the amount as a function of RPM, like the chart below. This one
shows warmup enrichment; the other screens work the same.
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 119
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