Figure 4-15. Fuel pump test setup.

Figure 4-15. Fuel pump test setup.

(e) Air bubbles on volume test indicates

(2) Pump pressure and volume test.

leaky fuel line or fuel pump.

(a) Start engine and run at 500 rpm.

(4) Vacuum test. The fuel pump vacuum test

(b) Insert volume test hose into graduated

is an auxiliary test that is necessary only when

c o n t a i n e r and open fuel discharge hose clamp.

pump output does not meet pressure or volume

When fuel reaches 4 ounce level, submerge end of

hose in fuel and observe for bubbles.

specifications. The fuel pump vacuum test is made

to determine whether the defect is in the pump or in

(c) Note time required to pump one pint of

fuel, then clamp fuel discharge hose.

the fuel line.

Caution: Dispose of fuel in graduated

(a) Close fuel tank shut-off valve.

container to avoid a fire hazard. Adequate fuel

(b) Disconnect tank fuel delivery line at

fuel pump.

delivery is available when a full pint flows in 30

seconds or less at 500 rpm.

pump inlet and attach vacuum gage hose.

(d) With engine still running at 500 rpm,

(d) Start engine and run at idle speed

note gage reading on fuel pump tester. The gage

reading is static pressure of fuel pump and reading

s u f f i c i e n t to permit vacuum gage to reach its

maximum reading.

should be 3 pounds per square inch (rein) to 5

pounds per square inch (max).

(e) Stop engine and observe vacuum gage

for 10 or 15 seconds.

(3) Results and indications.

within

(5) Results and indications.

and

volume

(a) P r e s s u r e

(a) If maximum vacuum is 8 inches or

specifications indicate fuel pump and lines are in

more, and does not fall off when engine is stopped,

satisfactory condition.

pump valves and filter bowl gaskets do not leak.

(b) Pressure and volume

indicates a

(b) If maximum reading is less than 8

defective fuel pump, restricted or leaky fuel line.

inches or vacuum falls off rapidly, replace fuel

(c) Pressure low with correct volume in.

pump.

dicated defective fuel pump.

(d) P r e s s u r e n o r m a l w i t h i n s u f f i c i e n t

Note. Line from fuel tank can be tested for air leaks

volume indicates restricted or leaky fuel line, or

in a similar manner by connecting vacuum gage hose to fuel

line at tank end of line, and repeating test. A rapid fall-off of

defective fuel pump.

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