Data monitor – Holley COMMANDER 950 User Manual

Page 57

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DATA MONITOR –

Used for monitoring real-time engine parameters

Both the Main Fuel Map and Spark Map screens have a readout of real-time engine parameters above the graph. This is an
essential tool when tuning an engine. The following is an explanation of each readout:

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Mod – Indicates the percent modification to the base fuel injection pulse width only when the engine is operating closed

loop. 100 would mean that no correction is occurring. 120 would mean that the computer is adding 20% more fuel to the
base pulse width value. A value of 80 would mean that the computer is subtracting 20% from the base pulse width.

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Comp Graph – There is a small bar graph that is a graphical representation of whether the computer is adding or

subtracting fuel in a closed loop mode. If the bar graph reads to the right, the computer is adding fuel because the base pulse
width is leaner than stoichiometric. If the bar graph reads to the left, the computer is subtracting fuel because the base pulse
width is rich. The far left or right of the scale indicates a fuel change of 10% at least.

Rich/Lean Indicator Light – This light includes the voltage output from the oxygen sensor in large numbers to aid in tuning
when the air/fuel ratio is leaner than 14.7:1; it will turn red. When the air/fuel ratio is richer than 1437:1, it will turn yellow.
When the voltage is higher than .75V, it will turn green. This signifies a safe air/fuel ratio under load.

RPM – Indicates actual engine speed

Spk Adv – Show current spark advance

IAC Position – Indicates the position of the pintle on the idle air control motor. This is a very important reading for adjusting
idle. The scale reads from 10 (closed) to 200 (fully open). If the idle is too high and this value is 10, the IAC can not close
further, which means that the throttle plates must be closed instead. If the idle is too low and the value is 200, the IAC is fully
open and can not add more air, which means that the throttle plates must be opened more.

dTPSdt – Indicates the rate of change of the throttle position sensor.

dMAPdt – Indicates the rate of change of the MAP sensor.

MAP – Shows the manifold pressure: if 1 bar, will vary between 0-100, 2 bar=0-200, and 3 bar=0-300.

TPS – shows the position of the throttle position sensor

MAT – Manifold air temperature in degrees Fahrenheit

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– Show the output voltage from the oxygen sensor. The range is 0 to 1 volt.

V Bat – Indicates battery voltage

Coolant – Indicates the coolant temperature in degrees Fahrenheit

MAT Mod – Indicates the modification to the base fuel pulse width based on intake air temperature. Based off of a percentage
of 100%.

Clt Mod – Indicates the modification to the base fuel pulse width based on coolant temperature. Based off of a percentage of
100%.

Aft Mod – Indicates the fuel afterstart modifier—percentage based.

Atm Mod – Indicates modification due to atmospheric conditions (Alpha –N only)—percentage based. This only shows up if
“N” is selected.

Inj PW – Indicates fuel injector pulse width. Units are milliseconds.

Duty Cycle – Indicates the amount of time injectors are open based on a percentage of available on and off time. This is
important to make sure it is not over 85% (ideally) at wide-open throttle to reduce injector overheating. If it is 100 then the
injectors are fully open (static) and can not provide any more fuel to the engine. If you enter a value in the injection volume
table that will drive the system to a static condition, that cell will become red. This value will have to be lowered. If more fuel
is needed the fuel pressure can be raised, or larger injectors are needed. Labels on the left indicate status of various functions
by changing the background color. For example, you will notice that the “Fuel Pump On” will highlight when the fuel pump is
running.

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