203d - Fuel System Service

Question 1

A micron is ______ of a meter?

Answer 1

1 millionth of a meter
0.000001m

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Question 2

How wide is a human hair in microns?

Answer 2

70 microns

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Question 3

What is the smallest particle visible to the human eye?

Answer 3

40 microns

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Question 4

In injection pumps and injectors, precision machined parts are fitted with how small of clearances?

Answer 4

1-3 microns

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Question 5

What size of particles are the most damaging to fuel injection equipment?

Answer 5

5-20 microns

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Question 6

What are four basic types of fuel filters?

Answer 6

• Screen / strainer
• Surface
• Depth
• Edge

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Question 7

Where are screen type filters typically used?

Answer 7

Fuel tank inlet

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Question 8

What type of filter element do surface type filters use?

Answer 8

Pleated paper

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Question 9

What are two disadvantages of depth type fuel filters?

Answer 9

• Less efficient
• More expensive

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Question 10

How do edge type fuel filters work?

Answer 10

Trap particles as the fuel flows over ledges.

No micron rating. Not a positive method of filtration.

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Question 11

What are three common filter classifications?

Answer 11

• Primary (25 micron)
• Secondary (5 micron)
• Final stage

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Question 12

What are the general properties of a primary fuel filter?

Answer 12

• Typically 25 microns
• First filter after fuel tank
• Intended to protect the transfer pump
• Usually under a vacuum
• May be combined with a water separator

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Question 13

What are the general properties of a secondary filter?

Answer 13

• Typically 5 microns
• On the outlet side of transfer pump
• Under pressure

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Question 14

What are the general properties of a final stage fuel filter?

Answer 14

• Typically 1 micron
• Located just before the injection pump
• Under pressure

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Question 15

Oil filters incorporate a bypass valve as a safety feature if they become plugged.

Do fuel filters also contain a bypass valve?

Answer 15

No. All fuel must be filtered.

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Question 16

When is the greatest chance for fuel system contamination to occur?

Answer 16

During refuelling or fuel filter maintenance.

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Question 17

Is it better to pre-fill fuel filters or use the built-in hand priming pump?

Answer 17

Use the hand priming pump. Less chance of contamination.

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Question 18

What would result from air entering the fuel system?

Answer 18

• Reduced volume of injected fuel
• Delayed injection timing
• Rough running engine

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Question 19

What are five basic types of fuel transfer pumps?

Answer 19

• Diaphragm
• Plunger
• Hand primer
• Gear
• Vane/blade

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Question 20

What causes a diaphragm pump to enter a neutral pumping state?

Answer 20

When the pressure on the outlet side equals the diaphragm spring force.

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Question 21

How are diaphragm transfer pumps self regulating?

Answer 21

Diaphragm spring tension controls max pressure.

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Question 22

What pressures do diaphragm fuel transfer pumps operate at?

Answer 22

• 3-5 psi operating pressure
• Max 10 psi

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Question 23

Where are plunger type fuel transfer pumps typically mounted?

Answer 23

On the injection pump housing and driven by an eccentric on the pump camshaft.

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Question 24

Fuel flow through a plunger type fuel transfer pump is controlled by a set of:

Answer 24

Check valves

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Question 25

What pressures do plunger type fuel transfer pumps operate at?

Answer 25

Maximum 25-30psi
Operating pressure is set by the injection pump overflow valve.

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Question 26

On a plunger type transfer pump, why should the hand priming pump shaft be seated and locked in place when not in use?

Answer 26

• Keep air, dirt, and water from entering pump
• Prevent fuel leakage

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Question 27

Is a gear type transfer pump a positive or non-positive displacement pump?

Answer 27

Positive displacement. Must have a relief valve to set maximum pressure.

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Question 28

What range should be selected for a pressure gauge?

Answer 28

A range no greater than twice the pressure being measured.

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Question 29

What sets the inlet supply fuel pressure to a port & helix injection pump?

Answer 29

Overflow valve

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Question 30

Where should a vacuum gauge be installed when checking for fuel inlet restriction?

Answer 30

As close as possible to the transfer pump inlet.

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Question 31

What are typical maximum inlet fuel restriction amounts for clean and dirty fuel filters?

Answer 31

Clean filter: 3 inHg
Dirty filter: 6 inHg

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Question 32

Where would a pressure gauge be connected to measure fuel supply pressure to an injection pump?

Answer 32

On the outlet side of the transfer pump after the secondary filter.

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Question 33

What could cause low fuel pressure at the inlet of an injection pump?

Answer 33

• High transfer pump inlet restriction
• Restricted fuel lines
• Plugged fuel filters
• Worn transfer pump
• Relief valve stuck open

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Question 34

What are two methods of testing for air in the fuel?

Answer 34

• Submerge the return line in a bucket and watch for bubbles
• Instal a sight glass in the fuel line before the transfer pump inlet

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Question 35

For every 10 degrees Fahrenheit above 100 degrees, engine power decrease by:

Answer 35

1%

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Question 36

To avoid system contamination, what two methods should be used to fill fuel filters during fuel filter service?

Answer 36

• Use the hand primer/transfer pump
• Use pre-filtered fuel