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LEGV5151-02

- 27 -

Lesson Plan 2: Slide/Text Reference

10/02

Medium Engine Fuel Systems

SLIDE 1

• Start with review

LAST

To start our study of Medium Engine Fuel Systems, we will briefly review some performance concepts and terminology that were covered in depth in the Small Engine Fuel Systems Course.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

To rq ue

POWER CURVES REVIEW

rs Ho

e

we po

r

FTS

FLS

BSFC 00 RPM

Peak Torque

Governed Point

High Idle

SLIDE 2

• Instructor note

• High idle question

• High idle answer

With the slide displayed on the board, point out various items on the tent curve and ask the students the following review questions. As you get their responses, correct them or make additional comments as needed, using the answers shown below. How would you describe high idle. What tolerance is applied to it?

High idle is the maximum engine speed that can be achieved with no load on the engine as it is installed. This will vary with different parasitic loads. The high idle shown on the engine data tag is a bare engine high idle before any extra devices such as alternators, power steering pumps etc. have been installed. Normal tolerances for a heavy duty high idle is +40/-80 rpm. The high idle screw is a stop for maximum deflection of the governor spring which, when multiplied by spring rate, would give a governor spring force.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02 • Droopquestion

What do we call the portion of the curve that is available (with limited power) in the rpm range between the governed point and high idle?

• Droopanswer

Droop or Overrun

• Droopquestion

How much droop is typical for a truck application? For a generator set? For other applications?

• Droopanswer

Truck engines typically have 7-10% droop. Power generation requires 0-3%, and other applications generally have 5-7%.

• FLS question

The governed rpm point in the tent curve is labelled “FLS”. What does this stand for, and what does it mean?

• FLS answer

FLS stands for Full Load Setting. FLS is the rack position required in order to produce advertised governed horsepower for an engine rating. This setting is displayed on the engine plate. FLS is the point at which the full load screw is first in full contact with the stop or torque spring, if so equipped.

• FTS question

Describe the point on the curve that is labelled “FTS”. What does this stand for, and what does it mean?

• FTS answer

FTS stands for Full Torque Setting. As the engine is lugged below governed speed, flyweight force lowers with a constant governer spring force. This delta P of governor spring force would cause the rack position to increase. Before movement can happen, the force must first be great enough to bend the torque spring. When the force is greater than the torque spring, the rack position increases until the torque screw comes in contact with the solid stop. This rack position is Full Torque Setting (FTS).

• Horsepower question

Why does the horsepower curve reach its maximum at the rpm where FTS occurs?

• Horsepower answer

The horsepower curve (and the boost curve which is not shown here) get their shape from the fuel rate curve. Since the largest injection volume and the greatest number of injections per unit of time occur at FTS, the maximum horsepower will also occur near the FTS rpm.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02 • Horsepower question • Horsepower answer

Why does the horsepower decrease as the engine lugs below FTS? As the engine lugs below FTS, the injection volume stays the same, but there are fewer injections per unit of time. Since fuel rate decreases, horsepower also decreases. With some curves the power remains flat for a period and then falls off (light torque spring, typically with smaller FTS). With some curves the power falls off immediately when the engine goes below governed (no torque spring). With each of these curve shapes, something within the governor is different.

• Torque question

• Torque answer

Why does the torque curve continue to increase as the horsepower curve is decreasing? The torque curve is the one that the customer really uses. It is the pound feet of twisting force that propels whatever is being turned. The torque curve does not follow the fuel rate curve. Instead it continues to rise with lower rpm and fuel rate. This is caused by slower pistons speeds giving the fuel more time to burn and by reduced parasitic loads on the engine.

• BSFC question

Please explain what “BSFC”stands for, and give a brief description

• BSFC answer

The efficiency of the engine is recorded by the use of BSFC (Brake Specific Fuel Consumption). This is the amount of fuel in pound per horsepower hour or grams per kilowatt hour. The smaller the number, the more efficient the engine. The engines are designed to provide the best fuel efficiency at the recommended operating rpm. This number changes with both rpm and power demand. The curve shown is a full load BSFC curve.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES REVIEW

To rq ue

Given Information:

rs Ho

e ow p e

r

FTS

FLS

High Idle

2262 RPM

Governed

2100 RPM

Peak Torque

1400 lb ft @ 1200 RPM

Torque at Governed

1000 lb ft

Calculate: Horsepower at Governed

00 RPM

Peak Torque

Governed Point

High Idle

SLIDE 3

• Instructor note

This slide provides some example numbers so that the students can review the horsepower formula. Distribute the Engine Performance Reference (LEXT1044) and have them refer to the formula page. After they have done the calculation, show the next slide so that they can check their method. Explain as necessary.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES REVIEW Calculating Horsepower: HP = T x RPM HP = (1000 x 2100) + 5252 HP = 400

SLIDE 4

• Instructor note

LAST

After the students have done the calculation shown on the previous slide, show this slide so that they can check their method. Explain as necessary.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES REVIEW

To rq ue

Given Information:

rs Ho

e ow p e

r

FTS

FLS

High Idle

2262 RPM

Governed

2100 RPM

Peak Torque

1400 lb ft @ 1200 RPM

Torque at Governed

1000 lb ft

Calculate: Torque rise

00 RPM

Peak Torque

Governed Point

High Idle

SLIDE 5

• Instructor note

LAST

Ask students to calculate the torque rise for this engine, using the given information. After they have an answer, show the next slide so that they can check their method.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES REVIEW Calculating Torque Rise: TR = [(Peak Torque - Governed Torque) + Governed Torque] x 100% TR = [(1400 - 1000) + 1000] x 100% TR = (400 + 1000) x 100% TR = .4 x 100% TR = 40%

SLIDE 6

• Instructor note

LAST

After the students have done the calculation shown on the previous slide, show this slide so that they can check their method. Explain as necessary.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES REVIEW

To rq ue

Given Information:

rs Ho

e ow p e

r

FTS

FLS

High Idle

2262 RPM

Governed

2100 RPM

Peak Torque

1400 lb ft @ 1200 RPM

Torque at Governed

1000 lb ft

Calculate: % Droop

00 RPM

Peak Torque

Governed Point

High Idle

SLIDE 7

• Instructor note

LAST

Ask students to calculate the % Droop for this engine, using the given information. After they have an answer, show the next slide so that they can check their method.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES REVIEW Calculating Droop (Overrun): Droop = [(High Idle RPM - Governed RPM) + Governed RPM] x 100% Droop = [(2262 - 2100) + 2100] x 100% Droop = (162 + 2100) x 100% Droop = .077 x 100% Droop = 7.7%

SLIDE 8

• Instructor note

After the students have done the calculation shown on the previous slide, show this slide so that they can check their method. Explain as necessary.

• Droop question

Based on the % Droop, what kind of engine must this be?

• Droop answer

It is a truck application. As mentioned earlier, truck engines usually have 7-10% droop.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

MANUFACTURING TEST CONDITIONS • Rated horsepower ± 3% occurs at SAE J1995 conditions – – – – –

35° API fuel density @ 60°F 85°F fuel temperature 110°F inlet manifold temperature - ATAAC 77 °F inlet air temperature - JWAC 29.61 inches of hg air pressure (test cell) (30.50 inches of hg in field)

SLIDE 9

• Review correction factors

Now let’s quickly review horsepower correction factors. The engine is only guaranteed to make rated horsepower under conditions stated in SAE specification J1995. Any deviation from these standard conditions affects performance either positively or negatively. This slide shows the manufacturing test conditions at which our engines are tested. It is not a Caterpillar specification; it is used by all major engine manufacturers.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

MANUFACTURING TEST CONDITIONS • What horsepower should be expected from a 3406C, rated 425 horsepower @ 2100 rpm, under the following conditions? – – – –

40° API fuel density at 90° F 135° F fuel temperature at filter base 105° F inlet manifold temperature 30.05 inches of hg air pressure

SLIDE 10

• Sample problem

Here is a sample problem to review the process of calculating expected horsepower from an engine that is operating under nonstandard conditions.

• Instructor note

Have the students refer to the Engine Performance Reference (LEXT1044) to work through the problem. Assist them with the use of the correction factor charts as necessary. The following slides build a table that shows the answers one by one, so that the students can check their work.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Sample Problem Fuel density corrects to ??° API @ 60°F Fuel density correction factor

????

Fuel temperature correction factor ???? Air temperature correction factor

????

Baro. pressure correction factor

????

Total correction factor

????

SLIDE 11

• Fuel density @ 60°F

First, correct the fuel density to 60°F. The answer is 38° API at 60°F, as shown on the next slide. Since the API number is greater than 35, the fuel is less dense than standard. There will be a reduction of power. The fuel density correction factor that we find in the table will be greater than 1.000.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Sample Problem Fuel density corrects to 38° API @ 60°F Fuel density correction factor

????

Fuel temperature correction factor ???? Air temperature correction factor

????

Baro. pressure correction factor

????

Total correction factor

????

SLIDE 12

• Density correction factor

Now find the fuel density correction factor. The factor is 1.012, as shown on the next slide. This correction factor means that there will be a 1.2% loss of power due to less than standard fuel density. To find the % variation from standard, subtract the correction factor from 1.000, and multiply the result by 100%. In this case: 1.000 - 1.012 = -.012 -.012 x 100% = -1.2%

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Sample Problem Fuel density corrects to 38° API @ 60°F Fuel density correction factor

1.012

Fuel temperature correction factor ???? Air temperature correction factor

????

Baro. pressure correction factor

????

Total correction factor

????

SLIDE 13

• Fuel temperature correction factor

LAST

Now find the fuel temperature correction factor. The factor is 1.050, as shown on the next slide.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Sample Problem Fuel density corrects to 38° API @ 60°F Fuel density correction factor

1.012

Fuel temperature correction factor 1.050 Air temperature correction factor

????

Baro. pressure correction factor

????

Total correction factor

????

SLIDE 14

• Inlet air temperature correction factor

Now find the air temperature correction factor. The factor is .997, as shown on the next slide. This correction factor is very close to 1.000, because the air inlet temperature in this example (105°F) is very close to standard (110°F). Although the effect will be slight, the factor is less than 1.000 so there will be a positive effect on power.

• To find % deviation from standard

To find the % variation from standard, subtract the correction factor from 1.000, and multiply the result by 100%. In this case: 1.000 - .997 = .003 -.003 x 100% = +.3%

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Sample Problem Fuel density corrects to 38° API @ 60°F Fuel density correction factor

1.012

Fuel temperature correction factor 1.050 Air temperature correction factor

0.997

Baro. pressure correction factor

????

Total correction factor

????

SLIDE 15

• Barometric pressure correction factor

LAST

Now find the barometric pressure correction factor. The factor is 1.003, as shown on the next slide.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Sample Problem Fuel density corrects to 38° API @ 60°F Fuel density correction factor

1.012

Fuel temperature correction factor 1.050 Air temperature correction factor

0.997

Baro. pressure correction factor

1.003

Total correction factor

????

SLIDE 16

• Total correction factor

With all the correction factors calculated, the next step is to multiply them times each other to arrive at the total correction factor: 1.012 x 1.050 x .997 x 1.003 = 1.063

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Sample Problem Fuel density corrects to 38° API @ 60°F Fuel density correction factor

1.012

Fuel temperature correction factor 1.050 Air temperature correction factor

0.997

Baro. pressure correction factor

1.003

Total correction factor

1.063

SLIDE 17

• High fuel temperature is main reason for low power in this example

LAST

The total correction factor shows that performance will be reduced by 6.3%. The main reason is the high fuel temperature. The expected horsepower under these operating conditions can be calculated by dividing the rated horsepower by the total correction factor (see next slide).

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Sample Problem So . . . what horsepower should be expected from our example 3406C rated 425 hp @ 2100? 425 + 1.063 = 400 horsepower

SLIDE 18

• 15 or more HP is noticeable

As seen, the exected horsepower is 400. This would more than likely cause a performance complaint. Generally, a loss of 15 horsepower or more can be noticed by the operator.

• If measured, multiply

Note: If the engine horsepower had been an actual measured value, we would multiply the measured value by the TCF to get a corrected horsepower value. This corrected value should then be within +/- 3% of rated power.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES Set Point FTS FLS Set Point – Governed speed + 20 rpm

Set point: The point at which the rack screw is in contact with the torque spring 10% to 45% of the time

00

RPM

Governed speed 2100

High Idle - 2262

SLIDE 19

• Set point definition

• Critical adjustment

LAST

Set Point is the rpm at which the full load screw is in contact with the torque spring between 10% and 45% of the time. If we then load the engine down 20 more rpm below set point, the full load screw will be first in contact with the torque spring 100 percent of the time, which is the FLS or governed point. Therefore, governed is always 20 rpm below where we find set point. We set governed speed by use of set point, since we can not exactly determine the first point of 100 percent contact. Set point is a critical engine adjustment, because it affects the rpm where governed point, FLS, FTS, and rated horsepower will occur.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES Raise High Idle Horsepower FTS

00

RPM

FLS

Governed speed 2100 High Idle - 2262

SLIDE 20

• Effect of raising High Idle (set point, FLS, FTS also increase)

Now, let’s consider the effect of adjusting high idle to a higher rpm. When high idle is raised, the rpm at which we achieve FLS goes up. Since FLS rpm is higher, set point is higher. The reason for this is that spring rate does not change, so the intersection point of FLS and the droop curve occurs at a higher rpm.

• Fuel rate is higher

Since we get FLS at a higher rpm, fuel rate at the new governed speed is higher. This happens because we get the same injection volume as we had before at FLS, but there are more injections per unit of time. The same is true of FTS setting and fuel rate. The new fuel rate and horsepower curves are represented by the yellow curve in this slide.

• Peak torque rpm not affected

As high idle rpm is increased, set point goes up on almost a one-to-one ratio. The governed point, FLS, and FTS go up a like amount, but peak torque rpm does not change. Peak torque rpm is a function of engine characteristics, such as turbocharger size and design. Therefore it is not affected by changine the high idle adjustment.

• Larger operating range

LAST

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02 operating range (from peak torque to governed point). If high idle is increased enough to cause set point to be out of tolerance (too high) the engine could be operated outside its emissions certification rpm range. If the engine is operated at the new (higher) governed point, horsepower will be slightly increased. Of course, nothing is free. The increased horsepower is due to an increase in fuel consumption.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES Lower High Idle Horsepower

FLS

FTS

00

RPM

Governed speed 2100 High Idle - 2262

SLIDE 21

• Effect of lowering High Idle (set point, FLS, FTS also decrease)

• Fuel rate is lower

• Peak torque rpm not affected • Smaller operating range

LAST

If high idle is lowered, the rpm at which we achieve set point will go down. Since set point rpm is lower, FLS rpm will be lower. Again, the reason for this is that spring rate does not change. The intersection point of FLS and the droop curve occurs at a lower rpm. Since we get FLS at a lower rpm, fuel rate at the new governed speed will be less. We will get the same injection volume as before the adjustment, but we will have fewer injections per unit of time. The same is true of FTS setting and fuel rate. With the lowered fuel rate, horsepower will be slightly less. With peak torque rpm remaining unchanged, the engine’s operating range will be reduced. The new fuel rate and horsepower curves are represented by the yellow curve in this slide.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES Raise Rack

00

RPM

Governed speed 2100

High Idle - 2262

SLIDE 22

• Increased rack setting gives lower set point

• Increased rack setting gives higher horsepower

LAST

The rack setting (FLS and FTS adjustment) also affects set point rpm. As the rack setting is increased, set point goes down. This happens because the rack can now travel farther before the FLS screw hits the torque spring. The engine must be loaded to a lower rpm than before, in order to reach set point. The change in set point is not as dramatic with a rack setting change as it is with a high idle change. Horsepower will be increased in proportion to the amount of rack change. Fuel consumption will also increase if the extra horsepower is used. At times, increased horsepower can actually improve fuel economy. An example would be a truck engine where the extra horsepower is only used to prevent the need for downshifting to a lower gear on a hill.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

POWER CURVES Lower Rack

00

RPM Governed speed 2100

High Idle - 2262

SLIDE 23

• Lowered rack setting gives higher set point

If the rack setting is decreased, set point rpm will increase. Again, the change in set point is not as dramatic as it is with an adjustment to high idle. Horsepower will decrease in proportion to the amount of rack change. Fuel consumption will decrease in most cases. However, if the lost horsepower causes premature gear changes (downshifts) in a truck application, fuel consumption could actually be increased.

• Lowered rack setting gives lower horsepower

The new fuel rate and horsepower curves are represented by the yellow curve in this slide.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Tolerances • High Idle = + 40 rpm / -80 rpm • Set Point: – Checking tolerance = +/- 25 rpm – Setting tolerance = +/- 10 rpm

SLIDE 24

• Set point regulated by adjusting high idle

• Installed engine high idle is less than bare engine high idle

Since set point is such a critical adjustment, it has a fairly restrictive adjustment tolerance. High idle has a much wider allowable rpm range. We regulate set point by adjusting high idle. The high idle rpm shown on the engine plate is for the bare engine, since there are no external parasitic loads on the engine at the factory test cell. High idle will normally be at a lower rpm when the engine is installed in its final application. If proper set point cannot be achieved by adjusting high idle within its tolerance (+40 / -80 rpm from the bare engine high idle setting), look for the following:

• Parasitic loads

• Excessive parasitic load on the engine will cause high idle to be too low, when set point is correct.

• Weak governor spring

• A weak governor spring will cause high idle to be too high when set point is correct.

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LEGV5151-02

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Lesson Plan 2: Slide/Text Reference

10/02

Lab Assignment • •

Check set point on the lab engine Adjust as needed

SLIDE 25

Introduce the Set Point lab as described in the next lesson plan.

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LEGV5151-02

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Lesson Plan 3

10/02

Medium Engine Fuel Systems Lesson Plan 3 - Set Point Lab Objectives: •

Working as a group, the students will check set point on a running engine, and make any necessary adjustments to bring it into the specified tolerance.

Literature Needed: Using the 6V2100 Multitach

SEHS7807

Using the 6V4060 Set Point Indicator Group

SEHS7931

Using the 9U7400 Multitach II Group

NEHS0605

Using the 4C6821 Injection Line Pickup Group

SEHS9363

Hardware Needed: Loadable engine that has set point Hand Tools 6V2100 Multitach 6V4060 Set Point Indicator 4C6821 Injection Line Pickup 9U7400 Multitach II Group Time Required: 1.00 Hour Tasks Required by Instructor to Meet Objectives: 1. Distribute and discuss handouts for set point tooling: A. Using the 6V2100 Multitach (SEHS7807) B. Using the 6V4060 Set Point Indicator Group (SEHS7931) C. Using the 4C6821 Injection Line Pickup Group (SEHS9363) D. Using the 9U7400 Multitach II Group

(NEHS0605)

2. Take the students to the lab to check set point on a loadable engine. A. Have them follow the Special Instruction literature to connect and program the 6V2100 Multitach and the 6V4060 Set Point Indicator Group to the engine. B. Have them check the engine oil and coolant levels. LAST

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LEGV5151-02

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Lesson Plan 3

10/02 C. Start and warm up the engine. B. Demonstrate loading the engine to measure set point. C. Have each student load the engine to measure set point and record their numbers. D. Have students calculate the average of the last five readings taken. (These readings may vary somewhat from initial readings, due to the engine oil temperature increase during the lab.) E. If necessary, have them adjust high idle to achieve the correct set point, and repeat the test. F. Demonstrate the use of the 9U7400 Multitach II Group, pointing out its advantages: 1. Display can show data for two engines simultaneously. 2. Display can hold set point value in memory.

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