1 speed density – Holley COMMANDER 950 User Manual

Page 14

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14

2.1 Speed Density

1. Engine speed (1000 RPM) and manifold pressure from the MAP sensor (38 kPa) are read by the ECU. From these

values, it obtains a number from the base fuel map (32).

2. The ECU then looks at the reading from the Air Temperature Sensor and may modify the fuel value. In this case it adds

.8% more fuel.

3. The ECU looks at the reading from the Engine Coolant Temperature Sensor and may further modify the value. In this

case it is at 100% (operating temperature) so it does not add or subtract more fuel.

4. The ECU will look and see if the engine is accelerating based on the Throttle Position Sensor. In this case the engine

speed is not changing.

5. From these values, it will calculate the amount of fuel that the user has programmed to deliver which is called the

pulsewidth. If the engine is closed loop, it will modify this value to maintain an air/fuel ratio of 14.7:1.

The following flowchart (Figure 1) illustrates this example:

BASE FUEL MAP

VALUE

100.8%

1000 RPM

38 kPa

32

47

°

F

AMOUNT OF FUEL

INJECTED

(Pulse Width)

3.1 ms

ENGINE

SPEED

MANIFOLD

PRESSURE

(MAP Sensor)

MANIFOLD AIR

TEMPERATURE

MODIFIER

(Air Temp Sensor)

ACCELERATION

ENRICHMENT

(change in TPS and

MAP Sensor)

COOLANT

TEMPERATURE

MODIFIER

(Water Temp Sensor)

100.0%

0.82v

CLOSED LOOP
FEEDBACK TO

MAINTAIN 14.7:1

AIR/FUEL RATIO

(Oxygen Sensor)

CLOSED LOOP

OR

OPEN LOOP?

AMOUNT OF FUEL

INJECTED

(Pulse Width)

3.8 ms

Open Loop

Closed Loop

180

°

F

100.0%

No Change

Sensor Data

Input

ECU Calculations

and Adjustments

Key:

Figure 1 Engine at Operating Temperature; Speed Density ECU Strategy Flowchart

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